RPGS_complete_Lecture_note.pdf

Renewable Power Generation System
Submitted By
Dr. Subhendu Sekhar Sahoo
Gandhi Institute For Technology

Renewable Power Generation Systems
Module I: (15 Hours)
Introduction: Conventional energy Sources and its Impacts, Non conventional energy–
Seasonal variations and availability, Renewable energy – sources and features, Distributed
energy systems and dispersed generation (DG). Solar Energy: Solar processes and spectral
composition of solar radiation. Solar Thermal system-Solar collectors, Types and
performance characteristics, Applications-Solar water heating systems(active & passive) ,
Solar space heating & cooling systems , Solar desalination systems, Solar cooker. Solar
photovoltaic system-Operating principle, Photovoltaic cell concepts, Cell, module,
array, Losses in Solar Cell, Effects of Shadowing-Partial and Complete Shadowing, Series
and parallel connections, Cell mismatching, Maximum power point tracking, Applications
Battery charging,Pumping,Lighting,Peltier cooling. Modeling of PV cell.
Module II: (10 Hours)
Wind Energy: Wind energy, Wind energy conversion; Wind power density, efficiency limit
for wind energy conversion, types of converters, aerodynamics of wind rotors, power ~ speed
and torque speed characteristics of wind turbines, wind turbine control systems; conversion to
electrical power: induction and synchronous generators, grid connected and self excited
induction generator operation, constant voltage and constant frequency generation with power
electronic control single and double output systems, reactive power compensation,
Characteristics of wind power plant, Concept of DFIG.
Module III: (9 Hours)
Biomass Power: Principles of biomass conversion, Combustion and fermentation, Anaerobic
digestion, Types of biogas digester, Wood gassifier, Pyrolysis, Applications. Bio gas, Wood
stoves, Bio diesel, Combustion engine, Application.
Module IV: (6 Hours)
Hybrid Systems: Need for Hybrid Systems, Range and type of Hybrid systems, Case studies
Of Diesel-PV, Wind-PV, Microhydel-PV, Biomass-Diesel systems, electric and hybrid electric
vehicles.
Text Books:
[1] Godfrey Boyle“Renewable Energy- Power for a Sustainable Future”,Oxford
University Press.
[2] B.H.Khan, “Non-Conventional Energy Resources”,Tata McGrawHill, 2009.
[3] S. N. Bhadra, D. Kastha, S. Banerjee, “Wind Electrical Systems”,Oxford University
Press, 2005.
Reference Books:
[1] S. A. Abbasi, N. Abbasi, “Renewable Energy Sources and Their Environmental
Impact”, Prentice Hall of India, New Delhi, 2006
.Digital Learning Resources:
Course Name: Energy Resources and Technology
Course Link: https://nptel.ac.in/courses/108/105/108105058/
Course Instructor: Prof. S Banerjee, IIT Kharagpur

Module-1
Energy Sources:- Energy storage can be defined as means of storing energy in a readily
recoverable form when the supply exceeds the demand for use at other times. Storage of
primary fuels (e.g. coal, oil and gas) is also a form of energy storage, but the term ‘energy
storage’ generally applies to secondary energy rather than primary energy.
Classification:-
Energy resources can be classified on the basis of following criteria:
1. Based on Usability of Energy
a) Primary resources- Examples of primary energy resources are coal, crude oil, sunlight,
wind, running rivers, vegetation and radioactive material like uranium etc.
These resources are generally available in raw forms and are therefore, known as raw energy
resources. Generally, this form of energy cannot be used as such. These are located, explored,
extracted, processed and are converted to a form as required by the consumer.
(b) Secondary Resources The energy resources supplied directly to consumer for utilization
after one or more steps of transformation are known as secondary or usable energy, e.g.
electrical energy, thermal energy (in the form of steam or hot water), refined fuels or synthetic
fuels such as hydrogen fuels, etc.
2. Based on Traditional Use
(a) Conventional Energy resources, which are being traditionally used, for many decades and
were in common use around oil crisis of 1973, are called conventional energy resources, e.g.
fossil fuels, nuclear and hydro resources.
(b) Non-conventional Energy resources, which are considered for large-scale use after the oil
crisis of 1973, are called non-conventional energy sources, e.g. solar,wind, biomass, etc.
3. Based on Long-Term Availability
(a) Non-renewable Resources, which are finite and do not get replenished after their
consumption, are called non-renewable e.g. fossil fuels, uranium, etc. They are likely to deplete
with time.
(b) Renewable Renewable energy is energy obtained from sources that are essentially
inexhaustible. Examples of renewable resources include wind power, solar power, geothermal
energy, tidal power and hydroelectric power. The most important feature of renewable energy is
that it can be harnessed without the release of harmful pollutants.
4. Based on Commercial Application
(a) Commercial Energy Resource-The energy sources that are available in the market for a
definite price are known as commercial energy. Most important forms of commercial energy are
electricity, coal and refined petroleum products. Applications of solar energy, wind energy,
hydro energy for electricity and lifting water from the ground require technology are
termed as commercial energy sources.
(b) Non-commercial Energy The energy sources that are not available in the commercial
market for a price are classified as non-commercial energy. All energy sources which are
available in nature like wind, sun, hydro etc. are non-commercial energy sources. Non-
commercial energy sources include fuels such as firewood, cattle dung and agricultural wastes,
which are traditionally gathered, and not bought at a price, used especially in rural households.
5. Based on origin
(a) Fossil fuels energy
(b) Nuclear energy

(c) Hydro energy
(d) Solar energy
(e) Wind energy
(f) Biomass energy
(g) Geothermal energy
(h) Tidal energy
(i) Ocean thermal energy
(j) Ocean wave energy
Consumption trend of Primary Energy resources
The global average consumption trend of various primary energy resources of the
world is indicated in Fig. 1.
Fig .1
Importance of non-conventional energy sources
The concern for environment due to ever-increasing use of fossil fuels and rapid depletion of
these resources has led to development of alternative sources of energy, which are renewable
and environment friendly. Following points may be mentioned in this connection:
1. Conventional sources (except hydro) are non-renewable and finite assets. With present rate
of consumption their availability is rapidly declining.
2. The demand of energy is increasing exponentially due to rapid industrialization and
population growth, the conventional sources of energy alone will not be sufficient in the long
run, to meet the growing demand.
3. Conventional sources (fossil fuels, nuclear) also cause pollution leading to degradation of
the environment. Ultimately, their use has to be restricted within acceptable limits.
4. Large hydro resources affect wild life, cause deforestation and pose various social problems.
Due to these reasons it has become important to explore and develop nonconventional energy
resources to reduce too much dependence on conventional resources. However, the present
trend of developments of non-conventional sources indicate that these will serve as supplement
rather than substitute for conventional sources for some more time to come.
Realizing the importance of non-conventional energy sources, in March 1981 the government of
India established a Commission for Additional Sources of Energy (CASE) in the Department of
Science and Technology, on the lines of the Space and Atomic Energy Commissions.
Energy Chain
The energy available from primary energy source is known as raw energy. This energy
undergoes one or more transformation stages before supplying to consumer. The sequence of
energy transformations between primary and secondary energy (usable energy) is known as
energy chain or energy route.

Common forms of Energy
1. Electrical Energy
2. Mechanical Energy
3. Thermal Energy
4. Chemical Energy
Advantages and disadvantages of Conventional Energy Sources
Advantages
1. Cost : At present these are cheaper than non-conventional sources.
2. Security : As storage is easy and convenient, by storing certain quantity, the energy
availability can be ensured for certain period.
3. Convenience: These sources are very convenient to use as technology for their conversion
and use is universally available.
Disadvantages
1. Fossil fuels generate pollutants. Main pollutants generated in the use of these sources are
CO, CO2, NOx, SO2, particulate matter and heat. These pollutants degrade the environment,
pose health hazards and cause various other problems. COx is mainly responsible for global
warming also.
2. Coal is also a valuable petro-chemical and is used as raw material for various chemical,
pharmaceuticals and paints, etc. industries. From long-term point of view it is desirable to
conserve coal for future needs.
3. There are safety and technical issues with nuclear energy. Major problems associated with
nuclear energy are as follows:
(a) The waste material generated in nuclear plants has radioactivity of dangerous level; it
remains above safe limit for a long period of time and thus is a health hazard. Its safe disposal,
which is essential to prevent radioactive pollution, is a challenging task. Also the disposed
radioactive waste is required to be guarded for a long period (till its radioactivity level comes
down to a safe limit) in order to prevent against going in wrong hands.
(b) Possibility of accidental leakage of radioactive material from reactor (as happened in
Chernobyl, former USSR in April 1986)
(c) Uranium resource, for which the technology presently exists, has limited availability.
(d) Sophisticated technology is required for using nuclear resources. Only few countries
possess the required expertise to use nuclear energy.
4. Hydroelectric plants are cleanest but large hydro-reservoirs cause following problems:
(a) As large land area submerges into water, it leads to deforestation
(b) Causes ecological disturbances such as earthquakes

(c) Affects wild life
(d) Causes dislocation of large population and their rehabilitation problems
Salient Features of Non-Conventional Energy Sources
Merits
1. Non-conventional sources are available in nature free of cost.
2. They produce no or very little pollution. Thus by and large they are environment friendly.
3. They are inexhaustible(unlimited).
Demerits
1. In general the energy is available in dilute form from these sources.
2. Though available freely in nature the cost of harnessing energy from non-conventional
sources is generally high.
3. Uncertainty of availability: the energy flow depends on various natural phenomena beyond
human control.
4. Difficulty in transporting this form of energy.
5. Difficulty in storage.
Environmental Aspect of Energy
Greenhouse effect:- Carbon dioxide (CO2) envelope present around the globe in the atmosphere
behaves similar to a glass pane and forms a big global green house. This tends to prevent the
escape of heat from earth, which leads to global warming. This phenomenon is known as
greenhouse effect.
Apart from CO2, other gases behaving similar to CO2 include methane, nitrous oxide (NO),hydro
fluorocarbons (HFCs), chlorofluorocarbons (CFCs), hydro chlorofluorocarbons (HCFC), sulphur
hexafluoride, ozone and water vapor. These gases are known as greenhouse gases (GHG). Their
average concentrations in atmosphere along with Global Warming Potentials (GWPs) relative to
CO2 and atmospheric lifetimes are listed in Table 1.3.
Ex-
A chemical industry produces 5 Tg (teragrams) of NO per day. How much pollution is added
into the atmosphere per day in terms of carbon equivalent?
Solution:-The Global Warming Potential (GWP) of NO is 265.
The daily pollution of NO = 5 Tg
The daily pollution in terms of equivalent CO2 (ref. Table 1.3) = 5 × 265 = 1,325 Tg = 1,325
Million Tons of CO2
As (12/44) is the carbon to CO2molecular weight ratio, the pollution in terms of Million Metric
Tons of Carbon Equivalent (MMTCE) = 1,325 × (12/44)= 361.36 MMTCE
Global Warming:- ‘Global warming is the continuing rise in the average temperature of the
earth’s atmosphere and ocean’s surface due to greenhouse effect’.
4.

World total primary energy consumption by fuel in 2018
Coal (27%)
Natural Gas (24%)
Hydro (renewables) (7%)
Nuclear (4%)
Oil (34%)
Others (renewables) (4%)
World Energy Status
World energy consumption is the total energy produced and used by the entire
human civilization.
Closely related to energy consumption is the concept of total primary energy supply (TPES),
which – on a global level – is the sum of energy production minus storage changes.
Energy supply, consumption and electricity
Key figures (TWh)
Year
Primary energy
supply (TPES)
(MTOE)
Final energy
consumption
(MTOE)
Electricity
generation
(TWH)
1973 71,013
(Mtoe 6,106)
54,335
(Mtoe 4,672)
6,129
1990 102,569 – 11,821
2000 117,687 – 15,395
2010 147,899
(Mtoe 12,717)
100,914
(Mtoe 8,677)
21,431
2011
152,504
(Mtoe 13,113)
103,716
(Mtoe 8,918)
22,126
2012
155,505
(Mtoe 13,371)
104,426
(Mtoe 8,979)
22,668
2013
157,482
(Mtoe 13,541)
108,171
(Mtoe 9,301)
23,322
2014
155,481
(Mtoe 13,369)
109,613
(Mtoe 9,425)
23,816
2015
158,715
(Mtoe 13,647)
109,136
(Mtoe 9,384)
2017 162,494
(Mtoe 13,972)
113,009
(Mtoe 9,717)
25,606
1
converted from Mtoe into TWh (1 Mtoe = 11.63 TWh)
and from Quad BTU into TWh (1 Quad BTU = 293.07 TWh)
World total primary energy supply (TPES), or "primary energy" differs from the world final
energy consumption because much of the energy that is acquired by humans is lost as other
forms of energy during the process of its refinement into usable forms of energy and its transport
from its initial place of supply to consumers. For instance, when oil is extracted from the ground
it must be refined into gasoline, so that it can be used in a car, and transported over long

2018 World electricity generation (26,700 TWh) by source (IEA, 2019)[
Coal (38%)
Gas (23%)
Hydro and other (19%)
Nuclear (10%)
Solar PV and wind (7%)
Oil (3%)
World total primary energy consumption by fuel in 2018[2]
Coal (27%)
Natural Gas (24%)
Hydro (renewables) (7%)
distances to gas stations where it can be used by consumers. World final energy
consumption refers to the fraction of the world's primary energy that is used in its
final form by humanity.
In 2014, world primary energy supply amounted to 155,481 terawatt-hour (TWh)
or 13,541 million tonne of oil equivalent (Mtoe), while the world final energy
consumption was 109,613 TWh or about 29.5% less than the total supply.[11]
World
final energy consumption includes products as lubricants, asphalt and
petrochemicals which have chemical energy content but are not used as fuel. This
non-energy use amounted to 9,723 TWh (836 Mtoe) in 2015.[12]
Electricity Consumption
The total amount of electricity consumed worldwide was 19,504 TWh in 2013,
16,503 TWh in 2008, 15,105 TWh in 2005, and 12,116 TWh in 2000. By the end of
2014, the total installed electricity generating capacity worldwide was nearly
6.14 TW (million MW) which only includes generation connected to local electricity
grids.[16] In addition there is an unknown amount of heat and electricity consumed off-
grid by isolated villages and industries. In 2014, the share of world energy consumption
for electricity generation by source was coal at 41%, natural gas at 22%, nuclear at
11%, hydro at 16%, other sources (solar, wind, geothermal, biomass, etc.) at 6% and oil
at 4%. Coal and natural gas were the most used energy fuels for generating electricity.
The world's electricity consumption was 18,608 TWh in 2012.[citation needed] This figure is
about 18% smaller than the generated electricity, due to grid losses, storage losses,
and self-consumption from power plants (gross generation). Cogeneration (CHP) power
stations use some of the heat that is otherwise wasted for use in buildings or in
industrial processes.
In 2016 the total world energy came from 80% fossil fuels, 10% biofuels, 5% nuclear
and 5% renewable (hydro, wind, solar, geothermal). Only 18% of that total world energy
was in the form of electricity.[17] Most of the other 82% was used for heat and
transportation.

Total primary energy supply of 13,972 Mtoe by source in 2017 (IEA,
2019)[14]
Oil (32.0%)
Coal/peat/shale (27.1%)
Natural gas (22.2%)
Biofuels and waste (9.5%)
Hydro electricity (2.5%)
Others (renewables) (1.8%)
Nuclear (4.9%)
By source
Availability of resources and future trend
The energy sources like coal and petroleum products take million years for
production. These energy sources are going to be exhausted after few years. These
energy sources are termed as non-renewable energy sources.
Energy sources like solar, wind, hydro, various forms of biomass and marine
energy (wave & tidal) are never exhaustible. These are termed as renewable energy
sources. Geothermal and ocean thermal energy sources are also renewable energy
sources.
* The global primary energy supply and consumption is in table below.
Table: Annual primary energy consumption by fuel (2012) in Mtoe*
Nuclear (4%)
Oil (34%)
Others (renewables) (4%)

Mtoe- Million tons of oil equivalent.
Renewable Energy Sources:-
The capacity addition in renewable energy was about 27,300 MW in 2012.
Table: India’s Installed power generation capacity.
So, total renewable energy’s contribution becomes almost 33% (includes Hydro
power), plan wise grid connected renewable energy contribution is given in Table
below.
Table: Power densities of renewable energy sources and the conventional energy
forms.

Onshore wind energy potential is estimated to be around 49,130 MW at a height of
50 m. It is estimated that around 17% of wind energy is utilized whereas 25,000
MW Has been connected to the grid. Wind energy is considered to be a viable
source to tackle the energy problems.
About 1/4th
of energy used in India is in the form of biomass that consists of
firewood, cattle dung, agriculture waste etc. This sector is managed by rural people
without any technology, management and investment. Indian Govt. is promoting to
use biomass to make deficit of energy. Studies have estimated that the biomass has
potential of generating 17,000MW from agro and forest residues alone.
Biogas is a three decade old program across India which covers estimated 5 million
installations.
India has put a national policy to replace the diesel and petrol by the production of
biodiesel from Jatropha, Karanja and Mahua which has been tried for last two
decades; and ethanol was considered to be successful replacement of petrol in
transportation sector. The technology has been developed by Brazil in 1976 for
successful of petrol and diesel. About 95% of cars sold in Brazil are flexible to run
in both ethanol and petrol but this is not successful in India.
* Solar energy is distributed over the entire geographical region at the
rate of 5-6 kwh/m2
/day. This can be utilized for the purpose of energy utilization in
many thermal applications such as cooking or heating or in photovoltaic cells that
convert sunlight to electricity.
India has launched a solar mission with an aim to install 20,000MW grid solar
power, 2000MW off grid system, 20 million solar lights and20 million m2
solar
thermal collector by 2020.
Origin of Renewable Energy Sources:-
All available energy sources in the world that come from three different
primary energy sources.

(i) Isotropic dissociation in the core of the earth.
(ii) Movements of the planets
(iii) Thermonuclear reactions in the earth.
* The largest energy flow comes from solar radiation, which is also responsible for
the development of fossil energy sources, namely oil, coal and gas due to bio
conversion which has occurred million years ago. All available natural renewable
energy sources are presented in the diagram and their conversion is also shown
below.
* Another source of energy is the geothermal energy originates from the earth’s
surface itself . The theoretical potential of geothermal energy is much lesser (less
than by an order of 4) than the solar radiation.
* The third source of renewable energy is the movement of the planets . The force
of attraction between planets and gravitational pull creates tide in the sea. This
energy source magnitude is very less compared to geothermal energy.
Limitations:-
a) The real difficulty with the renewable energy sources are that the power density
of those energies are very less in comparison to conventional energy sources.

b) Since the solar and wind energies fluctuate with respect to day and season; the
surface area requirement will be large and so also storage device for heat and
electricity. The thermal energy storage system (sensible heat storage systems)
have low efficiency, while the phase change storage systems suffer density
variations in two phases and stability over several cycles. Electrical storage
device like batteries are heavy and not environment friendly.
New Delhi: India’s renewable capacity installations reached 86 gigawatt (GW) as
of 31 December, 2019, according to research firm JMK Research and Analytics.
Wind energy became the biggest contributor with 44 per cent share in the
total renewable energy mix followed by solar with 39 per cent share.Year wise
installation trends in India
Sources: MNRE, JMK Research
“In 2019, about 7.5 GW of new utility scale solar capacity was added, which is
about 14 per cent increase over the previous year. Another one GW was added
in rooftop solar installations,” it added.
About 2.4 GW of new wind capacity was added in 2019, which was a 10 per cent
increase over 2018.
Gujarat led the installations with commissioning of 1.4 GW of new wind projects
followed by Tamil Nadu with 650 MW and Maharashtra with 212 MW.
“Most of the wind projects allocated in 2018 and scheduled to commission in
2019 got delayed and are now likely to be commissioned in 2020. This delay in
wind projects is primarily attributed to various land availability issues and lack of
grid transmission availability,” the research firm added.

Karnataka led the market with about 2 GW of new solar capacity additions
followed by Rajasthan with 1.7 GW, Tamil Nadu with 1.5 GW, Gujarat with 936
MW, Andhra Pradesh with 917 MW, and Madhya Pradesh with 651 MW.
Distributed and Dispersed Generation
Distributed generation (DG) entails using many small generators, of 2-50 MW
output, situated at numerous strategic points throughout cities and towns, so
that each provides power to a small number of consumers nearby. While these
small generators might be solar or wind turbine units, generating units in this
category are most often highly efficient gas turbines in small combined cycle
plants, because these are the most economical choices. Although small
compared to traditional central station generators, such 2- 500 MW generating
units are large, both physically and electrically compared to the needs of
individual energy consumers., producing power for between 50 and 400
homes.
Dispersed generation refers to use of still smaller generating units, of less than
500 kW output and often sized to serve individual homes or businesses. These
units are small enough to fit into garages or, like central air-conditioners, on a
pad behind a house. Micro gas turbines, bel cells, diesel, and small wind and
solar PV generators make up this category.
Basics of Distributed generation (DG)
Distributed generators include, but are not limited to synchronous generators, induction
generators, reciprocating engines, micro-turbines (combustion turbines that run on high-energy
fossil fuels such as oil, propane, natural gas, gasoline or diesel), combustion gas turbines, fuel
cells, solar photo-voltaic, and wind turbines.
Applications of Distributed Generating Systems
There are many reasons a customer may choose to install a distributed generator.
• DG can be used to generate a customer’s entire electricity supply; for peak shaving
(generating a portion of a customer’s electricity onsite to reduce the amount of electricity
purchased during peak price periods); for standby or emergency generation (as a backup
to Wires Owner's power supply); as a green power source (using renewable
technology);or for increased reliability.
• In some remote locations, DG can be less costly as it eliminates the need for expensive
construction of distribution and/or transmission lines.
Benefits of Distributed Generating Systems
Distributed Generation:
1. Has a lower capital cost because of the small size of the DG (although the investment cost
per kVA of a DG can be much higher than that of a large power plant).
2.May reduce the need for large infrastructure construction or upgrades because the DG can be
constructed at the load location.

3.If the DG provides power for local use, it may reduce pressure on distribution and transmission
lines.
4. With some technologies, produces zero or near-zero pollutant emissions over its useful life
(not taking into consideration pollutant emissions over the entire product lifecycle ie. pollution
produced during the manufacturing, or after decommissioning of the DG system).
4. With some technologies such as solar or wind, it is a form of renewable energy. Can increase
power reliability as back-up or stand-by power to customers. Offers customers a choice in
meeting their energy needs.
Challenges associated with Distributed Generating Systems
• There are no uniform national interconnection standards addressing safety, power quality
and reliability for small distributed generation systems.
• The current process for interconnection is not standardized among provinces.
• Interconnection may involve communication with several different organizations.
• The environmental regulations and permit process that have been developed for larger
distributed generation projects make some DG projects uneconomical.
• Contractual barriers exist such as liability insurance requirements, fees and charges, and
extensive paperwork.
Solar Energy: Solar processes and spectral composition of solar radiation.
• Solar energy is an important, clean, cheap and abundantly available renewable energy. It
is received on Earth in cyclic, intermittent and dilute form with very low power density 0
to 1 kW/m2
.
• Solar energy received on the ground level is affected by atmospheric clarity,
degree of latitude, etc.
• For design purpose, the variation of available solar power, the optimum tilt angle of solar
flat plate collectors, the location and orientation of the heliostats should be calculated.
What is Solar Radiation?
Solar radiation is radiant (electromagnetic) energy from the sun. It provides light
and heat for the Earth and energy for photosynthesis. This radiant energy is
necessary for the metabolism of the environment and its inhabitants . The three
relevant bands, or ranges, along the solar radiation spectrum are ultraviolet, visible
(PAR), and infrared. Of the light that reaches Earth’s surface, infrared radiation
makes up 49.4% of while visible light provides 42.3% . Ultraviolet radiation makes
up just over 8% of the total solar radiation. Each of these bands has a different
impact on the environment.
• Solar radiation provides heat, light, and energy necessary for all living
organisms. Infrared radiation supplies heat to all habitats, on land and in the
water 24. Without solar radiation, Earth’s surface would be about 32°C
colder 25.

• Solar energy, received in the form of radiation, can be converted directly or
indirectly in to other forms of energy, such as heat and electricity. The major draw
backs of the extensive application of solar energy of
1. the intermittent and variable manner in which it arrives at the earth’s surface and
2. the large area require to collect the energy at a useful rate.
Energy is radiated by the sun as electromagnetic waves of which 99% have wave
lengths in the range of 0.2 to 4.0 micro meter (1 micro meter = 10-6 meter)
Solar constant
The sun is a large sphere of very hot gases, the heat being generated by various
kinds of fusion reactions. Its diameter is 1.39 X 106
km while that of earth is 1.27
X 104
km. the mean distance between the two is 1.5 X 108
km. although the sun is
large, its subtends angle of only 32 min. at the earth’s surface.
• The brightness of the sun varies from its center to its edge. However the
calculation purpose the brightness all over the solar disc is uniform.
The total radiation from the sun is 5762 degrees K(i.eK=Kelvin)
The rate at which solar energy arise at the top of the atmosphere is called the solar
constant Isc . This is the amount of energy received in unit time on a unit area
perpendicular to the sun’s direction at the mean distance of the earth from the sun.
The solar constant value varies up to 3 % throughout the year, because the
distance between the sun and the earth varies little throughout the year.
• The earth is close set of the sun during the summer and farthest during the
winter.
• This variation in distance produces sinusoidal variation in the intensity of
solar radiation I that reaches the earth.
Spectral distribution of solar radiation intensity at the outer limit of the
atmosphere .
➢ The luminosity of the Sun is about 3.86 x 1026 watts. This is the total
power radiated out into space by the Sun. Most of this radiation is in
the visible and infrared part of the electromagnetic spectrum, with
less than 1 % emitted in the radio, UV and X-ray spectral bands.
➢ The sun’s energy is radiated uniformly in all directions. Because the Sun is
about 150 million kilometres from the Earth, and because the Earth is about 6300
km in radius, only 0.000000045% of this power is intercepted by our
planet.

➢ The power of the sun at the earth, per square metre is called the solar
constant and is approximately 1370 watts per square metre (W m-2).
➢ The solar constant actually varies by +/- 3% because of the Earth's slightly
elliptical orbit around the Sun. The sun-earth distance is smaller when the Earth is
at perihelion (first week in January) and larger when the Earth is at aphelion (first
week in July). Some people, when talking about the solar constant, correct for this
distance variation, and refer to the solar constant as the power per unit area
received at the average Earth-solar distance of one “Astronomical Unit” or AU
which is 149.59787066 million kilometres. There is also another small variation in
the solar constant which is due to a variation in the total luminosity of the Sun
itself. This variation has been measured by radiometers aboard several
satellites since the late 1970's.
Solar Radiation Measuring Instruments (Radiometers)
A radiometer absorbs solar radiation at its sensor, transforms it into heat and
measures the resulting amount of heat to ascertain the level of solar radiation.
Methods of measuring heat include resulting amount of heat to ascertain the level
of solar radiation.
➢ Methods of measuring heat include taking out heatflux as a temperature
change (using a water flow pyrheliometer, a silver-disk pyrheliometer or a
bimetallic pyranograph) or as a thermoelectromotive force (using a thermoelectric
pyrheliometer or a thermo electric pyranometer).
In current operation, types using a thermopile are generally used.
➢ The radiometers used for ordinary observation are pyrheliometers and
pyranometers that measure direct solar radiation and global solar radiation,
respectively.
Pyrheliometers
A pyrheliometer is used to measure direct solar radiation from the sun and its
marginal periphery. To measure direct solar radiation correctly, its receiving
surface must be arranged to be normal to the solar direction. For this reason, the
instrument is usually mounted on a sun-tracking device called an equatorial mount.
The structure of an Angstrom electrical compensation pyrheliometeris shown in
Figure.2

This pyrheliometer has a rectangular aperture, two manganin-strip sensors (20.0
mm × 2.0 mm×0.02 mm) and several diaphragms to let only direct sunlight reach
the sensor. The sensor surface is painted optical black and has uniform absorption
characteristics for short-wave radiation. A copper constantan thermocouple is
attached to the rear of each sensor strip, and the thermocouple is connected to a
galvanometer. The sensor strips also work as electric resistors and generate heat
when a current flows across them.
Pyranometers:
A pyranometer is used to measure global solar radiation falling on a horizontal
surface. Its sensor has a horizontal radiation-sensing surface that absorbs solar
radiation energy from the whole sky (i.e. a solid angle of 2p sr) and transforms this
energy into heat. Global solar radiation can be ascertained by measuring thisheat
energy. Most pyranometers in general use are now the thermopile type, although
bimetallic pyranometers are occasionally found.
Sunshine recorder
The duration of bright sunshine in a day is measured by means of sun shine
recorder. The sun’s rays are focused by a glass sphere to a point on a card strip
held in a groove in spherical bowl mounted concentrically with the sphere.
Whenever there is a bright sun shine the image formed is intensive

enough to burn a part on the card strip. through out the day as sun moves across the
sky, the image moves along the strip. Thus, a burnt trace whose length is
proportional to the duration of sun shine is obtained on the strip.
Solar Radiation Data
Most radiation data is measured for horizontal surfaces. As shown in figure. It is
seen a fairly, smooth variations with the maximum occurring around noon is
obtained on a clear day. In contrast an irregular variation with many peaks and
valleys may be obtained on a cloudy day.
• Peak values are generally measured in April or may with parts of Rajasthan or
Gujarat receiving over 600 Langley’s per day.
• During the monsoon and winter months, the daily global radiation decreases to
about 300- 400 longley per day.
• Annual average daily diffuse radiation received over the whole country is
around 175 longleys per day.
• The maximum value is about 300 langleys in Gujarat in July, while the minimum
values between 75 and 100 langleys per day, are measured over many parts of
the country during November and December as winter sets in.
Solar radiation on tilted surface:
The rate of receipt of solar energy on a given surface on the ground depends on
the orientation of the surface with reference to the sun. A fully sun – tracking
surface that always faces the sun receives the maximum possible solar energy at
the particular location.
A surface of the same area oriented in any other direction will receive a smaller
amount of radiation because solar radiation is such a dilute form of energy, it is
desirable to capture as much as possible on a ground area. Most of the solar

collectors or solar radiation collecting devices are tilted at an angle to horizontal
surface with Y=0 facing south for tilted surface.
Solar Radiation through atmosphere:
For estimating efficiencies of the solar systems, one usually takes sky conditions of
AM =1.5 i.e. the radiation has to travel 1.5 times more through the atmosphere in
comparison to the normal incidence.
Solar radiation without any scattering suffers considerable losses at all wavelength
regions while passing through earth’s atmosphere. For certain wavelengths, the
atmosphere is completely opaque and it is not allowed to reach earth.
The solar radiation received on the earth without any scattering in the atmosphere
is known as beam or direct radiation. The solar radiation received on earth from
the sun with multiple scattering is known as diffused or sky radiation. Summation
of both these components yields global solar radiation. The atmosphere also
radiates energy to the earth and its intensity is higher than that of global radiation.
This radiation is included in the region of long-wavelength radiation to the
atmosphere. The earth also radiates back long-wavelength radiation to the
atmosphere and part of which gets absorbed.
Table: Radiation balance on a receiving surface on earth.

The Generalized Transmission Law:
The radiation balance of earth’s system fluctuates w.r.t. time and location. The
global radiation is affected by the wavelength of the scattering and absorptive
radiation phenomena in the atmosphere. These are termed as extinction in
meteorology. The radiation reaching the earth’s surface can be calculated as:
Integrating the above equation over the entire length of the atmosphere (m) yields
the general transmission law for radiation passage through the atmosphere, i.e.

Scattering by the atmosphere:-
The scattering of radiation by the atmosphere can be divided into two categories:
(i) Rayleigh scattering in molecules (f)
(ii) Mie scattering in aerosols.
The Rayleigh scattering takes place in particles, whose diameter is much smaller
than the wavelength of the incident radiation. These particles scatter the short
wavelength of radiation strongly. The scattered radiation is given by the
expression:
The solar radiation reaches on the earth surface depends upon the following
factors:
(1) Reflection of the extra terrestrial atmosphere and on the earth’s surface
(2) Scattering on the earth’s atmosphere.
(3) Absorption in the atmosphere.

Solar Collectors:-
Solar power has low density (1kW/m2
to 0.1kW/m2
) per unit area. Hence
large amount of solar power collection needs larger area. The solar collector being
the first unit in the solar thermal system, collects heat from solar radiation then
transfers to the transport fluid efficiently. The transport fluid utilizes the heat for
necessary purposes.
Classification:

Performance Indices: The following performance indices are measured in a
Solar collector.
(1)Collector efficiency:- It is defined as the ratio of the energy actually absorbed
and transferred to the heat-transport fluid by the collector (useful energy) to the
energy incident on the collector.
(2) Concentration ratio:- It is defined as the ratio of the area of the aperture of the
system to the area of the receiver. The aperture of the system is the projected area
of the collector facing (normal) to the beam.

(3) Temperature range: It is the range of temperature to which the heat transport
fluid is heated up by the collector.
There are three types of solar collectors based on the temperature ranges.
(i) Low temperature Systems(<1500
C):
(ii) Medium-temperature Systems(150-4000
C):
(iii) High-temperature Systems(400-10000
C):
FLAT-PLATE COLLECTORS:
❖ Flat-plate collectors are the most common solar collector for solar water-
heating systems in homes and solar space heating. A typical flat-plate
collector is an insulated metal box with a glass or plastic cover (called the
glazing) and a dark-colored absorber plate. These collectors heat liquid or air
at temperatures less than 180°F.Flat-plate collectors are used for residential
water heating and hydronic space-heating installations.
❖ The flat-plate collector is located in a position such that its length is aligned
with longitude and is suitably tilted towards south to have maximum
collection.
❖ Liquid Flat plate collectors:-The schematics of flat plate collectors are
shown in the figure (a) and (b). It consists of a black coated plate made of
metal or plastic, which absorbs all the solar radiation incident on it and
converts into heat. This plate is known as the absorber. Fluid channels are
welded below the absorber for carrying a heat transfer fluid generally water.
This transport fluid transports the heat from the absorber into the utilisation
purposes.
❖ Liquid flat plate collectors heat liquid as it flows through tubes in or adjacent
to the absorber plate. The simplest liquid systems use potable household
water, which is heated as it passes directly through the collector and then
flows to the house.

To reduce the heat losses, the back side and sides of the collector (below the
absorber)are covered with insulation. The front above of the absorber is covered
with one or two transparent glass sheets. The whole thing is sealed in a box or
some sort of casing. The working of the collector basically depends upon the
greenhouse effects. Flat plate collectors can convert solar radiation into heat upto
maximum 1000
C.
❖ Air flat-plate collectors are used primarily for solar space heating. The
absorber plates in air collectors can be metal sheets, layers of screen, or non-
metallic materials. The air flows past the absorber by using natural
convection or a fan. Because air conducts heat much less readily than liquid
does, less heat is transferred from an air collector's absorber than from a
liquid collector's absorber, and air collectors are typically less efficient than
liquid collectors.
❖ Air heating solar collectors are mostly used for agricultural drying and space
heating applications. The basic advantages are low sensitivity to leakage, less

corrosion and no need for additional heat exchanger. The main disadvantage is
the requirement of larger surface area for heat transfer and higher flow rate.
Flat Plate Collector Efficiency:-
The instantaneous collection efficiency of a flat plate solar collector is
defined as:
Concentrating collectors
❖ Unlike solar (photovoltaic) cells, which use light to produce electricity,
concentrating solar power systems generate electricity with heat.
Concentrating solar collectors use mirrors and lenses to concentrate and
focus sunlight onto a thermal receiver, similar to a boiler tube. The receiver
absorbs and converts sunlight into heat. The heat is then transported to a
steam generator or engine where it is converted into electricity.
❖There are three main types of concentrating solar power systems:
parabolic troughs, dish/engine systems, and central receiver systems.
❖ These technologies can be used to generate electricity for a variety of
applications, ranging from remote power systems as small as a few kilowatts
(kW) upto grid-connected applications of 200-350megawatts (MW) or more.
❖ A concentrating solar power system that produces 350MW of electricity
displaces the energy equivalent of 2.3 million barrels of oil.

Parabolic Trough Systems
Fig. 1 A parabolic trough
These solar collectors use mirrored parabolic troughs to focus the sun's energy to a
fluid-carrying receiver tube located at the focal point of a parabolically curved
trough reflector (see Fig.1 above). The energy from the sun sent to the tube heats
oil flowing through the tube, and the heat energy is then used to generate electricity
in a conventional steam generator. Many troughs placed in parallel rows are called
a "collector field." The troughs in the field are all aligned along a north south axis
so they can track the sun from east to west during the day, ensuring that the sun is
continuously focused on the receiver pipes. Individual trough systems currently
can generate about 80 MW of electricity. Trough designs can in corporate thermal
storage—setting aside the heat transfer fluid in its hot phase—allowing for
electricity generation several hours into the evening. Currently, all parabolic trough
plants are "hybrids," meaning they use fossil fuels to supplement the solar output
during periods of low solar radiation.
Dish Systems

Each dish produces 5 to 50 kW of electricity and can be used independently or
linked together to increase generating capacity.
Central Receiver Systems
Central receivers (or power towers) use thousands of individual sun-tracking
mirrors called "heliostats" to reflect solar energy onto a receiver located on top
of at all tower. The receiver collects the sun's heat in a heat-transfer fluid
(molten salt) that flows through the receiver. The salt's heat energy is then used
to make steam to generate electricity in a conventional steam generator, located
at the foot of the tower. The molten salt storage system retains heat efficiently,
so it can be stored for hours or even days before being used to generate
electricity. Therefore, a central receiver system is composed of five main
components: heliostats, receiver, heat transport and exchange, thermal storage,
and controls (see Fig. 3).
Receiver and generator Concentrator individual dish/engine systems currently can
generate about 25 kW of electricity.
Solar Two—a demonstration power tower located in the Mojave Desert—can
generate about 10 MW of electricity. In this central receiver system, thousands
of sun-tracking mirrors called heliostats reflect sunlight onto the receiver.
Molten salt at 554ºF (290ºC) is pumped from a cold storage tank through the
receiver where it is heated to about 1,050ºF (565ºC). The heated salt then moves
on to the hot storage tank. When power is needed from the plant, the hot salt is
pumped to a generator that produces steam. The steam activates a
turbine/generator system that creates electricity. From the steam generator, the
salt is returned to the cold storage tank, where it stored is and can be eventually
reheated in the receiver. By using thermal storage, power tower plants can
potentially operate for 65percent of the year without the need for a back-up fuel
source. Without energy storage, solar technologies like this are limited to annual
capacity factors near25 percent. The power tower's ability to operate for
extended periods of time on stored solar energy separates it from other
renewable energy technologies. Hot salt storage tank Steam generator 1,050˚F
Cold salt storage tank Condenser cooling tower554˚FSystem boundary
Substation Steam turbine and electric generator.

Applications of Solar Energy
• Crop And Grain Drying
• Space And Water Heating
• Solar Energy Applications for Agriculture
• Greenhouse Heating
• Remote Electricity Supply (Photovoltaic)
• Water Pumping
Solar Space And Water Heating
• Livestock and diary operations often have substantial air and water heating
requirements. Modern pig and poultry farms raise animals in enclosed
buildings, where it is necessary to carefully control temperature and air
quality to maximize the health and growth of the animals. These facilities
need to replace the indoor air regularly to remove moisture, toxic gases
odors, and dust. Heating this air, when necessary, requires large amount of
energy. With proper planning and design solar air/space heaters can be
incorporated into farm buildings to preheat incoming fresh air. These
systems can also be used to supplement.
• SOLAR WATER HEATER
The details of most common type of solar water heater are shown in schematic
diagram of Fig. 5.17. A tilted flat plate solar collector with water as heat
transfer fluid is used. A thermally insulated hot water storage tank is mounted

above the collector.The heated water of the collector rises up to the hot water
tank and replaces an equal quantity of cold water, which enters the collector.
The cycle repeats, resulting in all the water of the hot water tank getting heated
up. When hot water is taken out from hot water outlet, the same is replaced by
cold water from cold-water make up tank fixed above the hot water tank. The
scheme is known as passive heating scheme, as water is circulated in the loop
naturally due to thermos-siphon action. When the collector is fixed above the
level of hot water tank, a pump is required to induce circulation of water in the
loop and the scheme will be known as active (or forced) solar thermal
system. An auxiliary electrical emersion heater may be used as back up for use
during cloudy periods. In average Indian climatic conditions solar water heater
can be used for about 300 days in a year. A typical 100 liters per day (LPD)
rooftop, solar water heater costs approximately ` 15,000–21,900 (year 2015)
and delivers water at 60–80 °C. It has a life span of 10–12 years and payback
period of 2-6 years. Figure 5.18 shows the photograph of an installed and
operating solar water heater.
In other schemes the hot water from collector delivers heat to service water
through a heat exchanger. In this scheme an anti-freeze solution may be used as
heat transport medium to avoid freezing during cold nights.

Figure 5.18 Solar water heater
SOLAR PASSIVE SPACE HEATING AND COOLING SYSTEMS
Solar energy is also used for heating or cooling a building to maintain comfortable
temperature inside. Passive systems do not require any mechanical device and
make use of natural process of convection, radiation and conduction for transport
of heat.
Use of passive heating/cooling systems put restrictions on the building design to
make possible the flow of heat naturally. Such a specially designed building is
called “solar house”. The state of the art for passive cooling is much less developed
than for passive space heating. Natural passive cooling may not always be
sufficient to meet the requirement and at peak load, auxiliary means may also be
needed, but it greatly reduces the load on the air conditioner plant.
Active heating/cooling systems employ mechanical devices, e.g. pump, blower,
etc.to circulate the working fluid for transportation of heat and therefore special
building design is not necessary as required in the case of passive heating.
Nevertheless, careful building design and insulation is desirable and will be less
expensive than additional heating/cooling load due to poor design.
A solar passive space heating system is shown in Fig. 5.19. The south facing thick
wall, called ‘Trombe Wall’ is made of concrete, adobe, stone or composites of
brick blocks and sand, designed for thermal storage. In order to increase the
absorption, the outer surface is painted black. The entire south wall is covered by
one or two sheets of glass or plastic sheet with some air gap (usually 10–15 cm)
between the wall and inner glazing. Solar radiation after penetration through the
glazing is absorbed by the thermal storage wall. The air in the air gap between the
glazing and the wall thus gets heated, rises up and enters the room through the
upper vent

Figure 5.19 Solar space heating
while cool air from the room replaces it from the bottom vent. The circulation of
air continues till the wall goes on heating the air. Thus the thermal wall collects
stores and transfers the heat to the room. Heating can be adjusted by controlling the
airflow through the inlet and outlet vents by shutters. Opening the damper at the
top of the glazing allows the excess heat to escape outside, when heating is not
required.
Sometimes a reflective horizontal surface is also provided to make available the
additional radiation for thermal storage. A movable insulation cover (not shown in
figure) also sometimes used to cover the glaze to reduce the heat loss from the
storage wall to outside during night. In some models the thermal storage wall is
made up of water drums stacked over one another to increase the thermal storage
capacity. In another variation the thermal storage mass is provided above a metallic
roof of the building instead of a wall.
Solar desalination is a technique to produce water with a low salt concentration
from sea-water or brine (i.e Water with salt in it) using solar energy. There are two
common methods of solar desalination. Either using the direct heat from the sun or
using electricity generated by solar cells to power a membrane process.
• In the direct method, a solar collector is coupled with a distilling mechanism
and the process is carried out in one simple cycle.
• Water production by direct method solar distillation is proportional to the
area of the solar surface and incidence angle and has an average estimated value
of 3–4 litres per square metre (0.074–0.098 US gal/sq ft).
(A solar still distills water with substances dissolved in it by using the heat of
the Sun to evaporate water so that it may be cooled and collected, thereby
purifying it. They are used in areas where drinking water is unavailable, so that

clean water is obtained from dirty water or from plants by exposing them to
sunlight.)
(Distillation is the process of separating the components or substances from a
liquid mixture by using selective boiling and condensation.)
Indirect solar desalination employs two separate systems; a solar collection array,
consisting of photovoltaic and/or fluid-based thermal collectors, and a separate
conventional desalination plant. Production by indirect method is dependent on
the efficiency of the plant and the cost per unit produced is generally reduced by
an increase in scale.
Solar stills
The solar still is one of the oldest and by far the simplest water desalination
method. A solar still consists of a structural element called a basin covered with a
transparent material to allow the incident solar radiation to pass through to the
basin saline water for thermal absorption and evaporation. Solar energy absorption,
saline water evaporation, and fresh water condensation occur within a single
enclosure for a solar still. Solar stills are inherently direct collection systems. Solar
distillation using solar stills is considered to be a mature technology. Because it has
a low maintenance requirement, it is used worldwide to produce fresh water.
Typically, the basin is colored in dark or black to enhance solar flux absorption.
The water is heated by the solar rays absorbed by the basin, which increases the
water vapor pressure until some portion of the saline water evaporates as shown
in Figure 1. The water vapor moves upward and typically condenses on the cool
glass cover and run downs through a guiding channel to the collection reservoir.
There exist many types of solar stills, including single slope, double slope, single
and double basin, inverted, tubular, spherical, double effect multi wick, and
greenhouse integrated solar stills as shown in Figure 2.
Solar stills can be passive or active, depending on whether water circulation is
needed.
The main advantages of passive solar stills are that they do not require
electrical energy for pumping (passive solar collector ), it is simple, and it is easy
to operate.
However, the main drawback of the solar still is that it typically has low water
production due to the loss of latent heat of condensation through the solar still
transparent.

Transmissivity based on Reflection-Refraction
The direction of incident and refracted beams are related to each other by Snell’s
law as
follows:

As shown in Fig. 5.43, Ibn is the intensity of the incoming beam radiation striking
the interface of two medium at an angle of incidence of q. The reflected beam has
reduced intensity of Ir1 making an angle of reflection which is equal to angle of
incidence. The direction of incident and refracted beams are related to each other
by Snell’s law as follows:
Figure 5.43 Reflection and refraction of the incident beam
SOLAR COOKERS-
-By using Soar cooker, Solar energy can be used for cooking purposes.
Thermal energy requirements for cooking purpose forms a major share of total
energy consumed, especially in rural areas. Variety of fuels like coal, kerosene,
cooking gas, firewood, dung cakes and agricultural wastes are being used to meet
the requirement. Fossil fuel is a fast depleting resource and need to be conserved,
firewood for cooking causes deforestation and cow dung, agricultural waste, etc.,
may be better used as a good fertilizer. Harnessing solar energy for cooking
purpose is an attractive and relevant option. A variety of solar cookers have been

developed, which can be clubbed in four types of basic designs: (i) box type solar
cooker, (ii) dish type solar cooker,(iii) community solar cooker, and (iv) advance
solar cooker.
1. Box Type Solar Cooker
The construction of a most common, box type solar cooker is schematically shown
in Fig. 5.27. The external dimensions of a typical family size (4 dishes) box type
cooker are 60 × 60 × 20 cm. This cooker is simple in construction and operation.
An insulated box of blackened aluminum contains the utensils with food material.
The box receives direct radiation and also reflected radiation from a reflector
mirror fixed on inner side of the box cover hinged to one side of the box. The angle
of reflector can be adjusted as required. A glass cover consisting of two layers of
clear window glass sheets serves as the box door. The glass cover traps heat due to
greenhouse effect. Maximum air temperature obtained inside the box is around
140–160 °C. This is enough for cooking the boiling type food slowly in about 2–3
hours. It is capable of cooking 2 kg of food and can save 3–4 LPG cylinder fuel in
a year. Electrical backup is also provided in some designs for use during non-
sunshine hours. Its cost varies from Rs.5,000 to Rs.6,290 (year 2016) depending
on the type, size, quality and electrical backup facility etc. A more affordable,
folding type model of solar cooker, made of cardboard material is also developed.
2. Paraboloidal Dish Type (Direct Type) Solar Cooker
A specially designed paraboloidal reflector surface concentrates the beam radiation
at its focus, where a cylindrical brass vessel containing food material is placed. A
commercial dish type solar cooker, SK 14, developed by EG solar, an NGO of
Germany, and being manufactured in India is shown in Fig. 5.28. The vessel

directly receives the concentrated solar radiation. The reflector is periodically
adjusted to track the sun. A fairly high temperature of about 450 °C can be
obtained and a variety of food requiring boiling, baking and frying can be cooked
for 10–15 persons. It can save on fuel up to 10 LPG cylinders annually on full use.
Cooking time is approximately 20–30 minutes. The approximate cost of the cooker
is Rs.8,500 (year 2016).
3. Community Solar Cooker
Community solar cooker has been developed for indoor cooking. It has a large
automatically tracked paraboloidal reflector standing outside the kitchen. Solar
Thermal Systems The reflector reflects the sunrays into the kitchen through an
opening in its north wall.
A secondary reflector further concentrates the rays on to the bottom of the cooking
pot, which is painted black. It can cook all types of food for about 40–50 people
and can save up to 30 LPG cylinders in a year with optimum use.
In another design of community solar cooker, large numbers of automatically
tracked paraboloidal reflectors are installed in series and parallel combinations and
generate steam for cooking in community kitchen. It can cook food for thousands
of people in a short time depending upon its capacity. It is normally installed in
conjunction with a boiler that may also use conventional fuel when necessary.
Photovoltaic effect
Conversion of light energy in electrical energy is based on a phenomenon called
photovoltaic effect. When semiconductor materials are exposed to light, the
some of the photons of light ray are absorbed by the semiconductor crystal
which causes a significant number of free electrons in the crystal. This is the

basic reason for producing electricity due to photovoltaic effect. Photovoltaic
cell is the basic unit of the system where the photovoltaic effect is utilised to
produce electricity from light energy. Silicon is the most widely used
semiconductor material for constructing the photovoltaic cell. The silicon atom
has four valence electrons. In a solid crystal, each silicon atom shares each of its
four valence electrons with another nearest silicon atom hence creating covalent
bonds between them. In this way, silicon crystal gets a tetrahedral lattice
structure. While light ray strikes on any materials some portion of the light is
reflected, some portion is transmitted through the materials and rest is absorbed
by the materials.
The same thing happens when light falls on a silicon crystal. If the intensity of
incident light is high enough, sufficient numbers of photons are absorbed by the
crystal and these photons, in turn, excite some of the electrons of covalent
bonds. These excited electrons then get sufficient energy to migrate from
valence band to conduction band. As the energy level of these electrons is in the
conduction band, they leave from the covalent bond leaving a hole in the bond
behind each removed electron. These are called free electrons move randomly
inside the crystal structure of the silicon. These free electrons and holes have a
vital role in creating electricity in photovoltaic cell. These electrons and holes
are hence called light-generated electrons and holes respectively. These light
generated electrons and holes cannot produce electricity in the silicon crystal
alone. There should be some additional mechanism to do that.
When a pentavalent impurity such as phosphorus is added to silicon, the four
valence electrons of each pentavalent phosphorous atom are shared through
covalent bonds with four neighbour silicon atoms, and fifth valence electron does
not get any chance to create a covalent bond.
A PV Cell or Solar Cell or Photovoltaic Cell is the smallest and basic building
block of a Photovoltaic System (Solar Module and a Solar Panel). These cells
vary in size ranging from about 0.5 inches to 4 inches. These are made up of

solar photovoltaic material that converts solar radiation into direct current (DC)
electricity.
Materials used for photovoltaic include mono crystalline silicon, polycrystalline
silicon, microcrystalline silicon, cadmium telluride, and copper indium selenide
/sulfide.
Different Types of PV Cells
Many new styles of PV cells are being developed today but mainly two distinct
material:
1. Crystalline Silicon PV Cells (Mono crystalline)
These Solar Cells are manufactured from crystalline silicon. Many of you must be
knowing that silicon is the second most common material on Earth and is
abundantly found in sand. To make solar cells out of silicon, manufactured silicon
crystals are sliced to about 300 micrometers thick and coated to work as a
semiconductor to capture solar energy.
2. Thin-film or Polycrystalline PV Cells
Thin-film PV cells use amorphous silicon or an alternative to silicon as
a semiconductor. These solar cells are relatively flexible and can be directly
installed with building materials. They work great even during clouds when there
is low sun light. Here, the disadvantage is that thin-film PV Cells comparatively
generate less electricity than crystalline silicon cells.
Solar PV Module
A bare single cell cannot be used for outdoor energy generation by itself. It is
because (i) the output of a single cell is very small and (ii) it requires protection
(encapsulation) against dust, moisture, mechanical shocks and outdoor harsh
conditions. Workable voltage and reasonable power is obtained by interconnecting
an appropriate number of cells. Cells from same batch are used to make PV
module. This is done to ensure that mismatch losses are minimal in the module.
The electrically connected cells are encapsulated, typically by using two sheets
of ethylene vinyl acetate (EVA) at either side. EVA is a good electrical insulator,
transparent material and has very low water absorption. The encapsulant cannot
provide rigidity to the module, for which glass is provided at the front side of the
module. At the rear side of the module a hard polymer material, typically,
polyvinyl fluoride (PVF, also known as tedlar) is used. Theses layers are arranged
as shown in Fig. 6.29 and hermetically sealed to make it suitable for outside
applications for 20-30 years without environmental degradation. This assembly is
known as solar module a basic building block of a PV system. Most common
commercial modules have a series connection of 32 or 36 silicon cells to make it

capable of charging a 12 V storage battery. However, larger and smaller capacity
modules are also available in international market.
Fig 6.29 PV Module details
Cell Mismatch in a Module
In a module, a number of cells are interconnected, it is very important that these
cells should match as closely as possible. That means Voc , Isc, Vm and Im (or fill
factor) for all cells must be exactly same. Any mismatch in the characteristics of
these cells leads to additional mismatch loss. Therefore, peak power of the
combination is always less than the sum of individual peak power of the cells.
Only under ideal case when all cells are exactly identical that the resultant peak
power would be equal to arithmetic sum of that of its constituents. This is
elaborated as follows.
When two cells with mismatched characteristics are connected in series and load
is applied, both cells are bound to carry same current.
The composite characteristics of the combination can be obtained by adding the
individual output voltage of the cell corresponding to a common current, for all
operating points, as shown in Fig. 6.30. At a particular operating point, while one
cell may be operating at peak power, the other may not. Thus peak power of the
combination is always less than the sum of individual peak power of each cell.
This is also clear from the shape of composite characteristics, which has lower fill
factor. Also if such a combination is short circuited, equal and opposite voltages
V1
’
, and V2
’
are produced by individual cells and therefore, one cell will be
generating power while the other will be dissipating it. Had the two cells been
perfectly matched no power would be generated or dissipated.
Similar conclusion may be drawn by considering a parallel combination of
two mismatched cells. Here the voltages of the cells are bound to be equal, but the
currents will be different and hence the maximum power points. The conclusion
may be generalized for more than two cells connected in series or in parallel. It can
also be shown that larger the number of cells in a module more would be the
possibility and quantum of mismatch loss.
To reduce mismatch losses, modules are fabricated from cells belonging to same

batch. Also cell sorting is carried out to categorize cells having matched
parameters with specified tolerance.
Effect of Shadowing
Partial shadowing may have serious consequences and may completely damage a
module due to creation of hot spot. Let us examine the operation of a module under
the conditions of: (i) partial shadowing of a cell in an open circuited, series string
of cells and (ii) complete shadowing of one cell in a short circuited, series string of
cells.
When a cell is partially shadowed, the shadowed portion will not produce any
power but the remaining portion will remain active and produce power. The
generated voltage by illuminated portion will forward bias the parallel rectifier
corresponding to shadowed portion as shown in Fig. 6.31. If shadowed area is
relatively small, the large circulating current through it will result in excessive
heating of the shadowed portion. The phenomenon is known as hot spot effect and
may completely damage the module for prolonged partial shadowing.
A short-circuited, series string of (n + 1) cells with one cell completely shadowed
is shown in Fig. 6.32. Here the voltages produced by n illuminated cells add up and
appears as reverse bias voltage of nV volts across the shadowed cell. As long as
peak inverse voltage (PIV) of the shadowed cell is more than the reverse bias, no
current will flow. If, however, the PIV is less than total reverse voltage appearing
across the shadowed cell, current will flow through the string, dissipating large
power in the shadowed cell, leading to possible damage of the module. The
chances of damage to the shadowed cell, due to excessive heating, increase with

the number of cells in the string. If the string supplies a load instead of being short-
circuited, the chances of damage still persist through to a lesser extent. The damage
due to shadowing can be avoided by connecting a bypass diode across the affected
cell as shown in Fig. 6.32. This bypass diode would allow an alternative path for
the load current. During healthy operation, the bypass diode has no role as the cell
voltage would keep it reverse biased. Even so, its use would result some loss
because of finite reverse leakage current through it. It is neither practical, nor
required to incorporate a bypass diode across each cell in a module. It has been the
international practice to provide a bypass diode for every 18 crystalline silicon
solar cells in a series string. Thus, the internationally standard module with 34–36
cells would contain two bypass diodes placed inside its terminal box.
Solar Photovoltaic Panels
An array or Solar PV Cells are electrically connected together to form a PV
Module and an Array of such Modules are again electrically connected together to
form a Solar Panel. This connection is done by soldering using flux cored solder
wire and PV Ribbon.

Solar PV Panel
Several solar modules are connected in series/parallel to increase the
voltage/current ratings. When modules are connected in series, it is desirable to
have each module’s maximum power production occur at the same current. When
modules are connected in parallel, it is desirable to have each module’s maximum
power production occur at the same voltage. Thus while interconnecting the
modules; the installer should have this information available for each module.
Solar panel is a group of several Solar Photovoltaic Systems modules connected in
series-parallel combination in a frame that can be mounted on a structure. Fig. 6.33
shows the construction of module and panel.
Figure 6.34 shows a series-parallel connection of modules in a panel. In parallel
connection, blocking diodes are connected in series with each series string of
modules, so that if any string should fail, the power output of the remaining series
strings will not be absorbed by the failed string. Also bypass diodes are installed

across each module, so that if one module should fail, the output of the remaining
modules in a string will bypass the failed module. Some modern PV modules come
with such internally embedded bypass diodes.
Solar PV Array
In general, a large number of interconnected solar panels, known as solar PV array,
are installed in an array field. These panels may be installed as stationary or with
sun tracking mechanism. It is important to ensure that an installed panel does not
cast its shadow on the surface of its neighboring panels during a whole year. The
layout and mechanical design of the array such as tilt angle of panels, height of
panels, clearance among the panels, etc., are carried out taking into consideration
the local climatic conditions, ease of maintenance, etc.

MAXIMISING THE SOLAR PV OUTPUT AND LOAD MATCHING
To make best use of solar PV system, the output is maximized in two ways. The
first is mechanically tracking the sun and always orienting the panel in such a
direction as to receive maximum solar radiation under changing positions of the
sun. That means adjusting the panel such that the sun rays always fall normal to its
surface. The second is electrically tracking the operating point by manipulating the
load to maximize the power output under changing conditions of insolation and
temperature.

PV Cell or Solar Cell Characteristics
Do you know that the sunlight we receive on Earth particles of solar energy
called photons. When these particles hit the semiconductor material (Silicon) of a
solar cell, the free electrons get loose and move toward the treated front surface of
the cell thereby creating holes. This mechanism happens again and again and more
and more electrons (Negative Charge) flows towards toward the front surface of
the cell and creates an imbalance of electrons. Now, when the front (–) and back
(+) surface of the photovoltaic cell are joined by a conductor such as a copper wire
then electricity is generated.
PV Cell Working Principle to Generate Electricity
Solar cells convert the energy in sunlight to electrical energy. Solar cells contain a
material such as silicon that absorbs light energy. The energy knocks electrons
loose so they can flow freely and produce a difference in electric
potential energy, or voltage. The flow of electrons or negative charge creates
electric current.
Solar cells have positive and negative contacts, like the terminals in a Battery. If
the contacts are connected with a conductive wire, current flows from the
negative to positive contact. The Figure below shows how a PV cell works to
generate electricity.

How much Electricity can a PV Cell Generate
A single photovoltaic cell can produce about 1 to 2 watts of electricity. This energy
is too less for use in any household or for a commercial purpose.
In order to increase the output of electricity, several photovoltaic cells are
electrically connected together to form a photovoltaic module and these modules
are further electrically connected to form a photovoltaic panel / photovoltaic
array. The number of modules connected to form an array depends on the amount
of solar electrical energy needed.
Converting DC to AC Electricity
The PV cells generate DC or direct current. This DC electricity has to be converted
to AC or alternating current so that it can be used in a home lighting system or
running appliances. An inverter is used to convert DC to AC. This is same as
converting DC from a battery to AC.
Storing Electricity Generated by Solar Cells
The electricity generated by solar cells by using solar energy has to be stored so
that it can be used later as when required. This is done by running the current
into a bank of Solar Batteries.
Solar photovoltaic (PV) systems convert solar energy directly into electrical
energy.
Basic conversion device used is known as a solar photovoltaic cell or a solar cell.
Solar cells were first produced in 1954 and were rapidly developed to provide
power for space satellites based on semiconductor electronics technology.
Commercial photocells may have efficiencies in the range of 10–20 per cent and
can approximately produce an electrical energy of about 1 kWh per sq. m per day
in ordinary sunshine. Typically, it produces a potential difference of about 0.5 V
and a current density of about 200 A per sq. m. of cell area in full solar radiation of
1 kW per sq. m. A typical commercial cell of 100 sq-cm area–thus produces a
current of 2A. It has a life span in excess of about 20 years. As a PV system has no
moving parts it gives almost maintenance free service for long periods and can be
used unattended at inaccessible locations.
Major uses of photovoltaics have been in space satellites, remote radio
communication booster stations and marine warning lights. These are also
increasingly being used for lighting, water pumping and medical refrigeration in
remote areas especially in developing countries. Solar powered vehicles and
battery charging are some of the recent interesting application of solar PV power.
Major advantages of solar PV systems over conventional power systems are:

(i) It converts solar energy directly into electrical energy without going through
thermal-mechanical link. It has no moving parts.
(ii) Solar PV systems are reliable, modular, durable and generally maintenance
free.
(iii) These systems are quiet, compatible with almost all environments, respond
instantaneously to solar radiation and have an expected life span of 20 years
or more.
(iv) It can be located at the place of use and hence no or minimum distribution
network is required, as it is universally available.
It also suffers from some disadvantages such as:
(i) At present the costs of solar cells are high, making them economically
uncompetitive with other conventional power sources.
(ii) The efficiency of solar cells is low. As solar radiation density is also low, large
area of solar cell modules are required to generate sufficient useful power.
(iii) As solar energy is intermittent, some kind of electrical energy storage is
required, to ensure the availability of power in absence of sun. This makes
the whole system more expensive.
Energy Losses and Efficiency
The conversion efficiency of a solar cell is the ratio of electrical power output to
incident solar power. The optimum possible theoretical efficiency of 31 per cent
for an ideal solar cell under ideal conditions is obtained at band gap of 1.45 eV.
In laboratory studies, the highest reported conversion efficiency of a single
crystal silicon solar cell is about 24 per cent. Conversion efficiencies of
commercially produced single crystal solar cells are in the range 12–18 per cent.
Various loss mechanisms lead to limit the conversion efficiency of the cell. Some
of these losses are due to inherent nature of internal physical processes and
available input. These cannot be influenced by external means. The other
category of losses can be influenced by suitable selection of material, processing
technology and other parameters of the cell.
1. Loss of Low Energy Photons
The photons having energy, E less than the band gap energy, E do not get absorbed
in the material and, therefore, do not contribute to the generation of electron-hole
pairs. This is referred as transmission loss, and is almost equal to 23 per cent for a
single junction solar cell.
2. Loss Due to Excess Energy Photons
When the photon energy E is higher than the band gap energy EG, the excess
energy(E – EGG) is given off as heat to the material. For a single junction solar
cell, this is equal to about 33 per cent.
3. Voltage Loss
A fraction of developed voltage is lost due to Auger recombination. The Auger

recombination occurs at high level of carrier concentration (>1017). In this
process, an electron recombining with hole gives its energy to another electron in
the conduction band, pushing it into higher energy level. The second electron
then goes through several scattering steps before coming back to conduction
band edge.
4. Fill Factor Loss
This type of loss arises due to parasitic resistance (series and shunt resistance) of
the cell. In best case FF could be 0.89.
5. Loss by Reflection
There are losses due to reflection from the active surface of the cell. As a result, a
fraction of incident photons will not enter the bulk material. To minimize these
losses, the active surface must be properly treated, by suitable anti-reflective
coating and/or by having a pyramidal or textured structure as shown in Fig. 6.17.
6. Loss Due to Incomplete Absorption
It refers to loss of photons which have enough energy (i.e., E > E) to get absorbed
in the solar cell, but do not get absorbed due to limited solar cell thickness. As
discussed earlier, silicon is an indirect band gap material. Photons of adequate
energy require traveling some distance in bulk material in order to get absorbed. If
the thickness of the cell is not sufficient (approx. 100 micron) some photons will
pass through full thickness of the material without ever getting absorbed. In order
to utilize these photons, appropriate light-trapping schemes should be utilized such
as; a reflecting G back ohmic contact should be used on the backside, to enhance
photon absorption in thinner cells, as shown in Fig. 6.17.
7. Loss Due to Metal Coverage
In wafer-based solar cells, the contact to the front side of the cell is made in the
form of finger and bus bar. This metal contact shadows some light which can be up
to 10 per cent. Several approaches are adopted to minimize this loss, which include
one side contact cell, buried contact solar cell or transparent contacts as used in
thin film solar cells.
8. Recombination Losses
Not all the generated electron hole-pairs contribute to photocurrent because some
are killed due to recombination. The recombination could occur in the bulk of
material or more predominantly at the surface. This type of recombination can be
minimized by appropriate surface and bulk passivation techniques in order to
obtain high IL.
MAXIMUM POWER POINT TRACKER
When a solar PV system is deployed for practical applications, the I-V
characteristic keeps on changing with insolation and temperature. In order to

receive maximum power the load must adjust itself accordingly to track the
maximum power point.
The I-V characteristics of PV system, along with some common loads, are shown
in Fig. 6.36. An ideal load is one that tracks the maximum power point.
If the operating point departs significantly from maximum power point, it may be
desirable to interpose an electronic maximum power point tracker (MPPT)
between PV system and load. Generally MPPT is an adaptation of dc-dc switching
voltage regulator. Coupling to the load for maximum power transfer may require
either providing higher voltage at a lower current or lower voltage for higher
current. A buck-boost scheme is commonly used with voltage and current sensors
tied into a feedback loop using a controller to vary the switching times. Basic
elements of a buck boost converter that may be used in an MPPT are shown in Fig.
6.37. The output voltage of the buck-boost converter is given by:
Where, D is the duty cycle of the MOSFET, expressed as fraction (0 < D < 1).
Details of operation and design of the converter may be found in any standard
book of power electronics.

The power output of a PV system is given by:

RPGS_complete_Lecture_note.pdf

Batteries
As solar energy is not available continuously and steadily, some form of energy
storage is normally required in most PV systems. Lead acid battery, Nickle cadmium
battery and Lithium ion storage batteries are commonly used in PV applications for
this purpose. The principles of operation of these batteries are already covered in
Section 3.4.2. Some general parameters of batteries are discussed here.
(a) Battery Voltage Three types of voltage available across its terminals are
specified: (a) open circuit voltage (maximum voltage); (b) nominal or working voltage
(available operating voltage during use), (c) cut-off voltage (minimum voltage after
which the battery should be disconnected from the load for recharging). Rechargeable
batteries are available with nominal voltages of 3 V, 6 V, 12 V, 24 V, etc.
(b) Battery Capacity It is the maximum charge storage capacity of a battery
expressed in Ah. (Ampere-hour). Higher Ah requires more active material. Therefore,
as the Ah capacity of a battery increases, the size of the battery also increases.
Multiplying Ah with voltage gives energy storage of the battery in Wh (Watt-hours).
(c) Battery Life Cycle It is defined as the number of complete charge/discharge
cycles that a battery can perform before its storage capacity falls below 80 per cent of
its rated capacity. The aging process (for instance shedding of active material from
plates) results in gradual reduction in storage capacity over time. The battery can still
be used but its available storage capacity will be lower.
(d) State of Charge (SoC) The SoC at a particular instant indicates the amount of
charge available with the battery at that instant. In lead acid battery, the electrolyte’s
specific gravity provides a convenient indication of the state of charge of the battery.
(e) Depth of Discharge (DoD) This is a measure of energy withdrawn from the battery
expressed as percentage of its full capacity. If a battery has a state of charge as 60 per cent, it
indicates that its DoD is 40 per cent. The DoD increases as the battery is discharged more and
more. Large DoD adversely affects the life cycle of the battery.
(f) Discharge Rate or C-rating C-rating is defined as the charge or discharge
current given in terms of capacity of the battery divided by number of hours for full Solar
Photovoltaic Systems charge or discharge. For instance a 120 Ah capacity battery with C-rating
of C/10(or 0.1C), will have a charge or discharge current of 120/10 = 12 A. Similarly, a 180
Ah capacity battery with C-rating of C/20 (or 0.05C) will have a charge or discharge
current of 180/20 = 9 A.
(g) Self-discharge Self-discharge is the loss of stored charge (or energy) when the
battery is not in use. It is caused due to internal electrochemical processes and may be
considered as equivalent to having a small external load. The self-discharge capacity
increases with increase in temperature. Therefore, in order to reduce self-discharge,
batteries must be stored at lower temperatures. In SIL batteries some antimony is
alloyed with lead to improve mechanical strength. But it also results in increased
self-discharge of the battery.
Deep Discharge Batteries
Ordinary batteries are not allowed to discharge beyond 50 per cent DoD. Batteries allowed
discharging up to 80 per cent or more are known as deep discharge batteries.
In traction applications where batteries are used to supply the load for longer duration,
deep discharge batteries are used. Normal SLI (starting, lighting and ignition) batteries are
shallow discharge batteries. They cannot be used in such applications as battery life cycle is
significantly reduced due to deep discharge. In deep discharge batteries, the electrode plates
are made thicker and stronger to avoid possible wrap of plates. In case of lead acid batteries,
tubular batteries are used for such applications.
SLI batteries remain at float charging most of the time. They are normally subjected
to only 2–5 per cent depth of discharge during starting of a vehicle. Therefore, these
batteries use thin plates with large surface area to supply large current during starting
process.

Battery Temperature During Discharge
Both battery capacity and battery voltage decrease, if used at lower temperature. At
high temperature also, its capacity may decrease due to deterioration in chemical
reaction. Normally, the best battery performance is obtained in temperature range of
20 to 40 °C.
Battery Charging
Different methods of charging are suggested for different type of batteries. A lead acid
battery may be charged by constant current, constant voltage or a combination of the
two. A typical charging cycle for a lead acid battery is shown in Fig. 6.39. The lead acid
battery is charged in three stages: (i) constant-current charge, (ii) topping charge and
(iii) float charge (or trickle charge). The battery is first charged with a constant current
(specified in data sheet) until its terminal voltage reaches the float potential value,
VB, float (typically 2.3 V to 2.45 V per cell). The constant current charge applies the
bulk of the charge (about 70 per cent) and takes up roughly half of the required charge
time. Thereafter the battery is charged by constant voltage VB, float as the current into
the battery tappers off. This phase is known as topping charge phase and continues
for few hours to fill the remaining 30 per cent. The battery is fully charged when the Non-
Conventional Energy Resources current drops to a set low level. Subsequently the applied
voltage across the battery is reduced so that small amount of charge keeps trickling into the
battery. The float charge compensates for the loss caused by self-discharge. Lead acid battery
charging is sluggish and cannot be charged as quickly as other battery systems. current drops
to a set low level. Subsequently the applied voltage across the battery is reduced so that small
amount of charge keeps trickling into the battery. The float charge compensates for the loss
caused by self-discharge. Lead acid battery charging is sluggish and cannot be charged as
quickly as other battery systems.
SOLAR PV APPLICATIONS
Batteries used in PV Applications
The most commonly used batteries in PV applications are the lead acid and nickel cadmium
batteries. Lithium-ion and nickel-metal hydride are also used, but to a much lesser extent. Lead
acid batteries are most popular. These batteries perform well in deep discharging mode than
any other battery.
Grid Interactive PV Power Generation
The first large sized (1 MW p) grid interactive PV plant was installed in Lugo, in California, USA.
The second and largest (6.5 MWp) plant was installed in Carissa Plains, California, USA. Also
some other large sized plants are operating in various countries and many others are proposed
in Italy, Switzerland, Germany, Austria,Spain and Japan. Presently, the biggest solar PV plant of
579 MW capacity, solar star project, is located at Antelope valley, Los Angeles County,
California. This is followed by a 550 MW Desert Sunlight Star at Riverside County, and 550 MW
Topaz Solar farm at San Louis, Obispo County, California.
In India, a 221 MW solar PV plant at Chankara, Gujarat is the biggest plant.
Another 750 MW plant is underway at Rewa, MP.
A large number of small rooftop grid interactive systems are successfully being operated in
various parts of the world.
Water Pumping
Pumping of water for the purpose of drinking or for minor irrigation, during sunshine
hours, is very successful application of stand-alone PV system without storage. Water
pumping appears to be most suited for Solar PV applications as water demand increases during
dry days when plenty of sunshine is available. There would be less need of water during rainy
season when the availability of solar energy is also low.
SPV water pumping systems have been successfully used in many parts of the world in the
range of few hundred Wp to 5 kW.
An SPV water pumping system is expected to deliver a minimum of 15,000 liters per day for
200 Wp panel and 1, 70,000 liters per day for 2,250 Wp panel from suction of 7 meters and /
or a total head of 10 meters

on a clear sunny day. Three types of motors have generally been used: (i) permanent
magnet dc motor (in low capacity pumping systems), (ii) brush-less dc motors and
(iii) variable voltage and variable frequency ac motors, with appropriate electronic
control and conversion system. An SPV water pumping system for a fishing farm is
shown in Fig. 6.53.
Lighting
Figure 6.53 An SPV water pumping system for fishing form
Next to water pumping, lighting is the second most important and extensive application of
stand-alone solar PV system.
As lighting is required when sun is not available battery storage is essential. Energy efficient
compact fluorescent lamps (CFL) or low-pressure sodium vapour lamps(LPSVL) are used at 25–
35 kHz frequencies, as SPV is an expensive power source. Pole mounted out-door lighting,
shown in Fig. 6.54, is designed for 3–6 hours an evening. A typical system has two 35 W
modules connected in parallel, an 11W (900 lumens) CFL, a 90 or 120 Ah, 12 V storage battery
and associated electronics including inverter, battery charger and timer to switch on and off the
light. The approximate cost of one pole mounted streetlight is Rs 30,000.
Medical Refrigeration
Figure 6.54 Pole mounted SPV lighting
In many developing countries where such life-saving vaccines are in great demand, electricity is
not available to operate conventional refrigerators. WHO has specified technical details
for PV based refrigerators using solar energy for such applications. This has resulted

in success of WHO sponsored immunization program in these countries. The volume
of refrigerator chamber varies from 20-100 liters with freezer volume ranging from
10–35 liters. The PV module size ranges from 100 Wp to over 600 W with 12 V /24 V battery,
of 150 to over 600 Ah capacities. An SPV powered portable medical refrigerator is shown in Fig.
6.56.
Village Power
Figure 6.56 An SPV powered portable medical refrigerator
Solar PV power can be used to meet low energy demands of many remote, small,
isolated and generally unapproachable villages in most developing countries. Two
approaches have generally been used:
(i) Individual SPV system for every household
(ii) A centralized SPV plant to meet combined load demand of the whole
village
Telecommunication and Signaling
Solar PV power is ideally suited for telecommunication applications such as, local
telephone exchange, radio and TV broadcasting, microwave and other forms
of electronic communication links. This is because, in most telecommunication
applications, storage batteries are already in use and the electrical systems are basically
dc. An SPV for satellite earth station is shown in Fig. 6.57.
Figure 6.57 SPV for satellite earth station

Effect of shadowing on Solar PV panels
Solar cell losses, Advantages, Disadvantages and Applications
Theory of solar cells|Solar cell materials|solar cell array|solar cell power plant
SOLAR CELL || PRINCIPLE, CONSTRUCTION, WORKING, VI CHARACTERISTICS AND APPLICATIONS OF
SOLAR CELL
Link for Solar cell working
https://youtu.be/X0OZ6tpZ3Mc
https://youtu.be/c58uWGY66Z0
Link for SOLAR CELL,Module,Panel,Array
https://youtu.be/FNQzj98x_pA
https://youtu.be/Moovzsy15aw
Solar cell losses
https://youtu.be/LMoE7uleR18
https://youtu.be/roiNF6_kGFM
https://youtu.be/JTDSPjDSrS8
https://youtu.be/Be5eZcLY7FQ
Solar Cell mismatching
https://youtu.be/vj_VyVmCSQU
MPPT
https://youtu.be/61KOruxxxiU
https://youtu.be/5Us5mM87PU8
PV Cell modelling
https://youtu.be/rjLd6eJYMsI
https://youtu.be/RRebGefCFps

Module-II
Wind Energy
Wind power or wind energy is the use of wind to provide mechanical
power through wind turbines to turn electric generators and traditionally to do
other work, like milling or pumping.
• Wind power is a sustainable, renewable energy source that has a much
smaller impact on the environment compared to burning fossil fuels.
• Wind turbines convert the kinetic energy in the wind into mechanical
power.
• Wind turbines convert the energy in wind to electricity by rotating
propeller-like blades around a rotor. The rotor turns the drive shaft, which
turns an electric generator. Three key factors affect the amount of energy a
turbine can harness from the wind: wind speed, air density, and swept
area.
Equation for Wind Power
V=Wind speed, = Density of the air, A=Swept area of the turbine
A wind energy conversion system (WECS) is powered by wind energy and
generates mechanical energy that sends energy to the electrical generator for
making electricity. Fig. 1.3 shows the interconnection of a WECS. The generator of
the wind turbine can be a permanent magnet synchronous generator (PMSG),
doubly fed induction generator, induction generator, synchronous generator, etc.
Wind energy acquired from the wind turbine is sent to the generator. To achieve
maximum power from the WECS, the rotational speed of the generator is
controlled by a pulse width modulation converter. The output power of the
generator is supplied to the grid through a generator-side converter and a grid-
side inverter. A wind farm can be distributed in onshore, offshore, seashore, or
hilly areas. The WECS might be the most promising DG for future SG.

Figure 1.3. Wind energy conversion system.
Wind energy is an alternative to fossil fuels, it is plentiful, renewable, widely
distributed, clean, low cost, produces no emissions during operation, and uses a
tiny land area [14]. The effects on the environment are generally less problematic
than those from other conventional power sources. Due to the variable wind
speed, the output power of the WECS fluctuates and may create a frequency
deviation of the power grid. To solve this problem, much research has already
been conducted.
The world wind energy association (WWEA) published the key statistics of the
World Wind Energy Report 2013.
The world wind energy capacity reached 318.5 GW by end of 2013 (this was
282.2 GW in 2012). In total, 103 countries are today using wind power on
commercial basis. China was still by far the leading wind market with a new
capacity of 16 GW and a total capacity of 91.3 GW. Wind power contributes close
to 4% of the global electricity demand. For the year 2020, the WWEA predicts a
wind capacity of more than 700 GW [15].

Horizontal-axis wind turbine showing major components.
Two potential wind sites are compared in terms of the specific wind power
expressed in watts per square meter of area swept by the rotating blades. It is
also referred to as the power density of the site, and is given by the following
expression in watts per square meter of the rotor-swept area:
This is the power in the upstream wind. It varies linearly with the density of the
air sweeping the blades and with the cube of the wind speed. The blades cannot
extract all of the upstream wind power, as some power is left in the downstream
air that continues to move with reduced speed.
History of Wind-Mills:
The wind is a by-product of solar energy. Approximately 2% of the sun's energy
reaching the earth is converted into wind energy. The surface of the earth heats
and cools unevenly, creating atmospheric pressure zones that make air flow from
high- to low pressure areas. The wind has played an important role in the history
of human civilization. The first known use of wind dates back 5,000 years to
Egypt, where boats used sails to travel from shore to shore. The first true
windmill, a machine with vanes attached to an axis to produce circular motion,
may have been built as early as 2000 B.C. in ancient Babylon. By the 10th century

A.D., windmills with wind-catching surfaces having 16 feet length and 30 feet
height were grinding grain in the areas in eastern Iran and Afghanistan. The
earliest written references to working wind machines in western world date from
the12th century. These too were used for milling grain. It was not until a few
hundred years later that windmills were modified to pump water and reclaim
much of Holland from the sea.
A typical modern windmill looks as shown in the following figure. The wind-mill
contains three blades about a horizontal axis installed on a tower. A turbine
connected to a generator is fixed about the horizontal axis.
Like the weather in general, the wind can be unpredictable. It varies from place to
place, and from moment to moment. Because it is invisible, it is not easily
measured without special instruments. Wind velocity is affected by the trees,
buildings, hills and valleys around us. Wind is a diffuse energy source that cannot
be contained or stored for use else where or at another time.
Classification of Wind-mills:
Wind turbines are classified into two general types: Horizontal axis and Vertical
axis.
A horizontal axis machine has its blades rotating on an axis parallel to the ground
as shown in the above figure. A vertical axis machine has its blades rotating on an
axis per pendicular to the ground. There are a number of available designs for
both and each type has certain advantages and disadvantages. However,
compared with the horizontal axis type, very few vertical axis machines are
available commercially.
Horizontal Axis:

This is the most common wind turbine design. In addition to being parallel to the
ground, the axis of blade rotation is parallel to the wind flow. Some machines are
designed to operate in an upwind mode, with the blades upwind of the tower. In
this case, a tail vane is usually used to keep the blades facing into the wind. Other
designs operate in a downwind mode so that the wind passes the tower before
striking the blades. Without a tail vane, the machine rotor naturally tracks the
wind in a downwind mode. Some very large wind turbines use a motor-driven
mechanism that turns the machine in response to a wind direction sensor
mounted on the tower. Commonly found horizontal axis wind mills are aero-
turbine mill with 35% efficiency and farm mills with 15% efficiency.
Vertical Axis:
Although vertical axis wind turbines have existed for centuries, they are not as
common as their horizontal counterparts. The main reason for this is that they do
not take advantage of the higher wind speeds at higher elevations above the
ground as well as horizontal axis turbines.
The basic vertical axis designs are the Darrieus, which has curved blades and
efficiency of 35%,the Giromill, which has straight blades, and efficiency of 35%,
and the Savonius, which uses Renewable Energy Sources scoops to catch the wind
and the efficiency of 30%. A vertical axis machine need not be oriented with
respect to wind direction. Because the shaft is vertical, the transmission and
generator can be mounted at ground level allowing easier servicing and a lighter
weight, lower cost tower. Although vertical axis wind turbines have these
advantages, their designs are not as efficient at collecting energy from the wind as
are the horizontal machine designs. The following figures show all the above
mentioned mills.

There is one more type of wind-mill called Cyclo-gyro wind-mill with very high
efficiency of about 60%. However, it is not very stable and is very sensitive to
wind direction. It is also very complex to build.
Link for Videos
Wind Energy
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Wind Energy Conversion
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Main Components of a wind-mill :

Following figure shows typical components of a horizontal axis wind mill.
Rotor:
The portion of the wind turbine that collects energy from the wind is called the
rotor.
The rotor usually consists of two or more wooden, fiberglass or metal blades
which rotate about an axis (horizontal or vertical) at a rate determined by the
wind speed and the shape of the blades. The blades are attached to the hub,
which in turn is attached to the main shaft.
Drag Design:
Blade designs operate on either the principle of drag or lift. For the drag design,
the Wind literally pushes the blades out of the way. Drag powered wind turbines
are characterized by slower rotational speeds and high torque capabilities. They
are useful for the pumping, sawing or grinding work. For example, a farm-type
windmill must develop high torque at start-up in order to pump, or lift, water
from a deep well.
Lift Design:
The lift blade design employs the same principle that enables airplanes, kites and
birds to fly. The blade is essentially an airfoil, or wing. When air flows past the
blade, a wind speed and pressure differential is created between the upper and
lower blade surfaces. The pressure at the lower surface is greater and thus acts to
"lift" the blade. When blades are attached to a central axis, like a wind turbine

rotor, the lift is translated into rotational motion. Lift-powered wind turbines
have much higher rotational speeds than drag types and therefore well suited for
electricity generation.
Tip Speed Ratio:
The tip-speed is the ratio of the rotational speed of the blade to the wind speed.
The Larger this ratio, the faster the rotation of the wind turbine rotor at a given
wind speed. Electricity generation requires high rotational speeds. Lift-type wind
turbines have maximum tip-speed ratios of around 10, while drag-type ratios are
approximately 1.
Given the high rotational speed requirements of electrical generators, it is clear
that the lift-type wind turbine is most practical for this application.
The number of blades that make up a rotor and the total area they cover affect
wind turbine performance. For a lift-type rotor to function effectively, the wind
must flow smoothly over the blades. To avoid turbulence, spacing between blades
should be great enough so that one blade will not encounter the disturbed,
weaker air flow caused by the blade which passed before it. It is because of this
requirement that most wind turbines have only two or three blades on their
rotors.
Generator:
The generator is what converts the turning motion of a wind turbine's blades
into electricity. Inside this component, coils of wire are rotated in a magnetic field
to produce electricity. Different generator designs produce either alternating
current (AC) or direct current (DC), and they are available in a large range of
output power ratings.
The generator's rating, or size, is dependent on the length of the wind turbine's
blades because more energy is captured by longer blades.
It is important to select the right type of generator to match intended use. Most
home and office appliances operate on 240 volt, 50 cycles AC. Some appliances
can operate on either AC or DC, such as light bulbs and resistance heaters, and
many others can be adapted to run on DC. Storage systems using batteries store
DC and usually are configured at voltages of between
12 volts and 120 volts.

Generators that produce AC are generally equipped with features to produce the
Correct voltage of 240 V and constant frequency 50 cycles of electricity, even
when the Wind speed is fluctuating.
DC generators are normally used in battery charging applications and for
operating DC appliances and machinery. They also can be used to produce AC
electricity with the use of an inverter, which converts DC to AC.
Transmission:
The number of revolutions per minute (rpm) of a wind turbine rotor can range
between 40 rpm and 400 rpm, depending on the model and the wind speed.
Generators typically require rpm's of 1,200 to 1,800. As a result, most wind
turbines require a gear-box transmission to increase the rotation of the generator
to the speeds necessary for efficient electricity production. Some DC-type wind
turbines do not use transmissions. Instead, they have a direct link between the
rotor and generator. These are known as direct drive systems. Without a
transmission, wind turbine complexity and maintenance requirements are
reduced, but a much larger generator is required to deliver the same power
output as the AC-type wind turbines.
Tower:
The tower on which a wind turbine is mounted is not just a support structure. It
also raises the wind turbine so that its blades safely clear the ground and so it can
reach the stronger winds at higher elevations. Maximum tower height is optional
in most cases, except where zoning restrictions apply. The decision of what height
tower to use will be based on the cost of taller towers versus the value of the
increase in energy production resulting from their use. Studies have shown that
the added cost of increasing tower height is often justified by the added power
generated from the stronger winds. Larger wind turbines are usually mounted on
towers ranging from 40 to 70 meters tall.
Towers for small wind systems are generally "guyed" designs. This means that
there are guy wires anchored to the ground on three or four sides of the tower to

hold it erect. These towers cost less than freestanding towers, but require more
land area to anchor the guy wires.
Some of these guyed towers are erected by tilting them up. This operation can be
quickly accomplished using only a winch, with the turbine already mounted to the
tower top. This simplifies not only installation, but maintenance as well. Towers
can be constructed of a simple tube, a wooden pole or a lattice of tubes, rods, and
angle iron. Large wind turbines may be mounted on lattice towers, tube towers or
guyed tilt-up towers.
Towers must be strong enough to support the wind turbine and to sustain
vibration,wind loading and the overall weather elements for the lifetime of the
wind turbine. Their costs will vary widely as a function of design and height.
Wind Energy Conversion
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Horizontal and Vertical Axis Turbine
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Vertical Axis Wind Turbine
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Operating Characteristics of wind mills:
All wind machines share certain operating characteristics, such as cut-in, rated
and cutout wind speeds.
Cut-in Speed:
Cut-in speed is the minimum wind speed at which the blades will turn and
generate usable power. This wind speed is typically between 10 and 16 kmph.

Rated Speed:
The rated speed is the minimum wind speed at which the wind turbine will
generate its designated rated power. For example, a "10 kilowatt" wind turbine
may not generate 10kilowatts until wind speeds reach 40 kmph. Rated speed for
most machines is in the range of 40 to 55 kmph. At wind speeds between cut-in
and rated, the power output from a wind turbine increases as the wind increases.
The output of most machines levels off above the rated speed.
Most manufacturers provide graphs, called "power curves, "showing how their
wind turbine output varies with wind speed.
Cut-out Speed:
At very high wind speeds, typically between 72 and 128 kmph, most wind turbines
cease power generation and shut down. The wind speed at which shut down
occurs is called the cut out speed. Having a cut-out speed is a safety feature which
protects the wind turbine from damage. Shut down may occur in one of several
ways. In some machines an automatic brake is activated by a wind speed sensor.
Some machines twist or "pitch" the blades to spill the wind.
Still others use "spoilers," drag flaps mounted on the blades or the hub which are
automatically activated by high rotor rpm's, or mechanically activated by a spring
loaded device which turns the machine sideways to the wind stream. Normal
wind turbine operation usually resumes when the wind drops back to a safe level.
Betz Limit:
It is the flow of air over the blades and through the rotor area that makes a wind
turbine function. The wind turbine extracts energy by slowing the wind down. The
theoretical maximum amount of energy in the wind that can be collected by a
wind turbine's rotor is approximately
59%. This value is known as the Betz limit. If the blades were 100%efficient, a
wind turbine would not work because the air, having given up all its energy,
would entirely stop. In practice, the collection efficiency of a rotor is not as high
as 59%.A more typical efficiency is 35% to 45%.
A complete wind energy system, including rotor, transmission, generator, storage
and other devices, which all have less than perfect efficiencies, will deliver
between 10% and 30% of the original energy available in the wind.

The following plot gives the relationship between wind speed in KMPH and the
power density.
In the last column of the table, we have calculated the output of the turbine
assuming that the efficiency of the turbine is 30%. However, we need to
remember that the efficiency of the turbine is a function of wind speed. It varies
with wind speed.
Now, let us try to calculate the wind speed required to generate power equivalent
to 1square meter PV panel with 12% efficiency. We know that solar insolation
available at the PV panel is 1000 watts/m2
at standard condition. Hence the
output of the PV panel with 12% efficiency would be 120 watts. Now the speed
required to generate this power by the turbine with 30% efficiency can be
calculated as follows:
Turbine output required = 120 Watts/m2
Power Density at the blades = 120/ (0.3) = 400 watts/m2
Wind Power:-
Wind power is generated on account of flow of wind. The blow of wind takes
place due to density difference at two places on the surface of the earth. The
density difference occurs when the solar radiation differs on earth’s surface.
Most of the energy stored in wind is found in high altitudes, over flat areas. But
most of the potential is close to the coastal areas, approximately equivalent to

72 TW, or 54,000 Mtoe per year. The power of the wind is proportional to the
cubic power of the velocity. To assess the frequency of wind speeds at a
particular location, a probability distribution function is often fit to the
observed data. Different locations will have different wind speed distributions.
The worldwide wind generation capacity is 1,94,400 MW. India’s present
installed capacity is 2,000 MW.
Off-shore Wind Power:-
Offshore wind power refers to the installation of wind power plant in the water.
Better wind speeds are obtained if the installation is made in the water than
the land. Induction generators are often used for power generation. The power
generators behave differently due to fluctuation of wind speed during power
generation. So, the installation of advanced electromechanical generators are
highly essential.
The capacity factor of wind generator is the ratio of actual productivity in a year
to the theoretical maximum. The capacity factor of a wind generator varies
from 20-40%. The capacity factor arises due to the variation of wind speed at
the site and the generator size. The smaller generator would be cheaper and
achieve higher capacity factor. Conversely the larger generator would cost
more and produce smaller capacity factor.
* The wind power has low operating cost but it carries high capital cost.
Origin of Wind:
The flow of air starts when there is pressure difference between two places. The
region where solar radiation is less the atmospheric air gets low temperature
and hence low pressure region. On the contrary where the solar radiation is
high the atmospheric air gets heated and pressure is high. These differences in
atmospheric air pressure (pressure gradient) cause acceleration of the air
particles which is called wind.
The rotation of earth about its own axis creates Coriolis force which superimposes
on the pressure gradient. The direction of wind motion is affected by this
Coriolis force. In the Northern hemisphere, the moving object turns towards
right due to the effect of the Coriolis force if the observer moves in the
direction of wind movement. Similarly, the moving object turns towards left in
the southern hemisphere.
* In a friction free, rectilinear and stationary wind movement, the force due to
pressure gradient and Coriolis force are of same magnitude but in opposite
direction. The wind motion due to Coriolis force is known as geostropic wind.

Fig: Geostropic wind on the northern hemisphere
As a result of pressure difference, the air first moves towards low pressure region.
It then follows inclined movement towards right due to Coriolis force. This
inclination towards right continues till the magnitude of Coriolis force is exactly
equal to the pressure gradient force. At this point the wind moves in the
direction of isobars whose motion is in the same direction as that of geotropic
winds.

Fig(b): Simplified circulation system of the earth (WMO 1981)
If the path of the wind is curved, then the centrifugal force of the wind particle
are also affected by the pressure force and Coriolis forces. The air particles
close to the earth’s surface are affected by the frictional forces. There is a
formation of boundary layer over the surface due to these frictional forces.
These collective forces creates a mechanism up to the range of heights 300m to
600m. The wind velocity within this boundary layer is much smaller than that at
higher altitudes. The air flow motion in the form of parallel isobars deviate with
decreasing altitude.
In figure (a), the wind flow patterns near the surface of the earth at high and low
pressure region have been shown in the hemisphere region.
In figure (b), the circulation system of the earth has been shown. It consists of two
components: (i) Hadley circulation in the equator region and (ii) Rossby
circulation in the upper and lower region of the earth.
The operating power of Hadley circulation is the strong solar radiation at the
equator. The air gets heated, rises high and moves towards north and south,
where it is deviated towards east as result of Coriolis force. The air gets cooled
and sinks down in

the latitude region ±300
(+ North, – South) and flows back towards the equator,
where it is deviated towards west due to the Coriolis force. These are the
regions where local storms overlap and wind-flows are not always predictable.
In the northern and southern region around latitudes ±600
the westerly winds
of Rossby circulation dominate the region. These winds have wave-form
character and vary strongly in the flow patterns.
Wind Flow and Wind Direction:-
Wind speed is classified on representative scale of 12. The order of wind
classification is in m/sec or knots (1 nautical miles = 1.852km/hr). The direction
of wind are normally divided into eight segments: North, North-East, East,
South-East, South, South-West, West and North-West.

Recording of wind data:
The wind speed is measured by an anemometer and wind direction is measured
by a wind vane attached to a direction indicator. Anemometer works on one of
the following principles.
(i) The oldest and simplest anemometer is a swinging plate hung vertically and
hinged along its top edge. Wind speed is indicated by the angle of deflection of
the plate with respect to the vertical.
(ii) A cup anemometer consists of three or four cups mounted symmetrically
about a vertical axis. The speed of rotation indicates wind speed.
(iii) A hot-wire anemometer measures the wind speed by recording cooling effect
of the wind on a hot-wire. The heat is produced by passing an electric current
through the wire.
(iv) An anemometer can also be on sonic effect. Sound travels through still air at a
known speed. However, if the air is moving, the speed decreases or increases
accordingly.
(v) Wind speed can be recorded by measuring the wind pressure on a flat plate.
(vi) The other methods include the laser drop anemometer, the anemometer and
the SODAR Doppler anemometer.

Applications of Wind Power: Mechanical Power:-
(i) Wind Pumps
(ii) Heating
(iii) Sea Transport
Off-grid Electrical Power Source:(i) Machines of lower power with rotor diameter
of about 3m to 40-1000 Watt rating can generate sufficient electrical energy for
space heating and cooling of homes, water heating, battery charging and for
operating domestic appliances
such as fans, lights and small tools.
(ii) Applications of somewhat more powerful turbines of about 50 KW are
producing electrical power for navigation signals, remote communication,
weather stations and off-shore oil drilling platforms.
(iii) Intermediate power range, roughly 100 to 250 KW aero-generators can power
to isolated populations, farm cooperatives, commercial refrigerators and to
small industries.
(iii) For lifting water to hill, aero-generator is installed on the top of hill and
electrical energy is transmitted to a pump fixed at lower level.
Grid-Connected Electrical Power Source.
(i) Large aero-generators in the range of a few hundred KW to a few MW are
planned for supplying power to a utility grid. Large arrays of aero-
generators,known as wind farms are being deployed in open plains or off-shore
in shallow water for this purpose.
Wind Energy Converters:-
The wind energy converters convert wind energy to electrical and mechanical
energies.
Maximum Power Coefficient:The maximum power coefficient of the wind energy
can be defined as the ratio of the convertible power to the theoretically
maximum power from the available wind energy.

Components of a Wind Power Plant:
The different components of a wind converter are described below.
Wind Turbine:-
The wind rotors are various types depending upon number of blades, speed,
control system, gear box (or gear less), type of generator etc. All the machines
are based upon four basic concepts of rotor dynamics. These are given in the
table below.
Table: Classification of selected wind power converters (Hau 2002).
* After extensive field experience, horizontal-axis, three-blade wind rotor has
become an established system for field applications.

* In 1980s and 1990s, one and two-blade rotors were also developed because of
higher rotational speed. But due to instability experience in operation, these
were not used further.
* Gearless rotors are generally low speed converters which requires a special
generator.
Tower: -
A component that sustains the whole weight of the rotor and its components is
the tower. The tower should have sufficient height to operate the rotor at
desired speed. The tower should also be strong enough to sustain the static and
dynamic load of the rotor and vibrations during high and gusty winds. Tower
are constructed from concrete or steel. Off-shore wind machines are of lower
height because the wind speed is larger. So the foundations built in those cases
are costly.
Electric Generators:
Electrical generators convert the rotational energy into mechanical energy then to
electrical energy. Commercially available generators with slight modification
are used for converters with gear box. Specially designed three phase
generators are used for gearless converters.
Synchronous Generator:-
These generators are equipped with a fixed stator at the outside and a rotor at
the inside located on a pivoting shaft. Normally DC is supplied to the rotor to
create a magnetic field. When the shaft drives the voltage is created in the
stator whose frequency matches exactly the rotational speed of the rotor. This
type of generators are used most of the places but the disadvantage is that it
runs with constant speed of the rotor and fixed frequency. It is therefore not
suitable for variable speed operations in the wind plants.
Asynchronous Generator:
The asynchronous generator is electromagnetic generator. The stator of this
generator is made of numerous coils with three groups and is supplied with
three phase current. The three coils are spread around the stator periphery and
carry currents, which are not in phase with each other. This combination
produces a rotating magnetic field, which is the key feature of the
asynchronous generator. The angular speed of the rotating magnetic field is
called the synchronous magnetic field and is given by:
Where f = frequency of the stator excitation, p = number of magnetic pole
pairs.

The stator coils are embedded in slots of high permeability magnetic core to
produce a required magnetic fields intensity with low exciting currents. The
rotor in this generator is squirrel cage rotor with conducting bars embedded in
the slots of the magnetic core. The bars are connected at ends by a conducting
ring. The stator magnetic field rotates at the synchronous speed given above.
The relative speed between the stator and the rotor induces a voltage in each
rotor turn linking the stator flux V = (-dF/dt), F being the magnetic flux linking
the rotor turn.
Foundations:-
The type of foundations required to anchor towers and thus wind energy
converters, into the ground depends upon the plant size, meteorological and
operational stress and local soil conditions. Erection of wind converters on a
coastal line is much more costly. Depending on the soil conditions, there types
of foundations namely gravity foundation, monopole foundation and tripod
foundations are used . All these foundations are discussed in the beginning.
Turbine Rating:-
The normal rating of a wind turbine has no standard global rating. The power
output of a turbine is proportional to the square of the rotor diameter and also
to the cube of the wind speed.
* The rotor of a given diameter will generate different power at different wind
speed (like 300 KW at 7m/sec and 450 KW at 8 m/sec).
* Many manufacturers mention a combined rating specification like 300/30
means 300 KW generator and 30 m rotor diameter.
* Specific rated capacity (SRC) is often used as a comparative index defined as:
SRC = Generator Electrical Capacity/Rotor Swept Area.
Multiple Choice Questions and answers
1. What does Heating and cooling of the atmosphere generates?
a)Thermo line circulation
b) Radiation currents
c) Convection currents
d) Conduction currents
Answer: c
Explanation: Wind energy can be economically used for the generation of electrical energy.
Heating and cooling of the atmosphere generates convection currents. Heating is caused by
the absorption of solar energy on the earth surface.
2. How much is the energy available in the winds over the earth surface is estimated to be?
a) 2.9 X 120 MW
b) 1.6 X 107 MW

c) 1 MW
d) 5MW
Answer: b
Explanation: The energy available in the winds over the earth surface is estimated to be 1.6 X
107 MW which is almost the same as the present day energy consumption. Wind energy can
be utilized to run wind mill which in turn, is used to drive the generators.
3. How much wind power does India hold?
a) 20,000 MW
b) 12,000 MW
c) 140,000 MW
d) 5000 MW
Answer: a
Explanation: India has a potential of 20,000 MW of wind power. Wind power accounts
nearly 9.87% of India’s total installed power generation capacity. Generation of wind power
in India mainly account from southern state of India.
4. What is the main source for the formation of wind?
a) Uneven land
b) Sun
c) Vegetation
d) Seasons
Answer: b
Explanation: Wind is free and renewable form of energy, which throughout history has been
used to grind grain, power ships, and pump water. Wind is created when the sun unevenly
heat the earth surface.
5. Which country created wind mills?
a) Egypt
b) Mongolia
c) Iran
d) Japan
Answer: c
Explanation: The earliest known wind mills were in Persia (Iran). These early wind mills
looked like large paddle wheels. Centuries later, the people of Holland improved the basic
design of wind mill. Holland is famous for its wind mills.
6. “During the day, the air above the land heats up more quickly than the air over water”.
a) True
b) False
Answer: a
Explanation: During the day, the air above the land heats up more quickly than the air over water.
The warm air over the land expands and raises, and the heavier, cooler air rushes in to take its
place, creating winds.
7. What happens when the land near the earth’s equator is heated?
a) All the oceans gets heated up
b) Small wind currents are formed
c) Rise in tides
d) Large atmospheric winds are created
Answer: d
Explanation: The large atmospheric winds that circle the earth are created because the land

near the earth’s equator is heated more by the sun than the land near the north and south
poles. Wind energy is mainly used to generate electricity.
8. What type of energy is wind energy?
a) Renewable energy
b) Non-renewable energy
c) Conventional energy
d) Commercial energy
Answer: a
Explanation: Wind is called a renewable energy source because the wind will blow as long as
the shines. Wind power, as an alternative to burning fossil fuels, is plentiful, renewable,
widely distributed, clean, produces no greenhouse gas emissions during operation, consumes
no water, and uses little land.
9. What are used to turn wind energy into electrical energy?
a) Turbine
b) Generators
c) Yaw motor
d) Blades
Answer: a
Explanation: Wind turbine blades capture wind energy, a form of mechanical energy, and put it
to work turning a drive shaft, gearbox, and generator to produce electrical energy. Many factors
affects wind turbine efficiency including turbine blade aerodynamics.
10. What is the diameter of wind turbine blades?
a) 320 feet
b) 220 feet
c) 80 feet
d) 500 feet
Answer: b
Explanation: Large utility-scale wind turbines can now generate more than a MW of
electrical power each and deliver electricity directly in to the electric grid, these turbines are
placed at 200 feet height at the rotor hub and have blades which are 220 feet or more in
diameter.
11. At what range of speed is the electricity from the wind turbine is generated?
a) 100 – 125 mph
b) 450 – 650 mph
c) 250 – 450 mph
d) 30-35 mph
Answer: d
Explanation: Wind turbines are designed with cut-in wind speeds and cut-out speeds i.e. the
wind speeds when the turbines start turning or shut off to prevent drive train damage.
Typically, maximum electric generations occurs at speeds of 30-35mph.
12. When did the development of wind power in India began?
a) 1965
b) 1954
c) 1990
d) 1985
Answer: c
Explanation: The development of wind power in India began in 1990s. Presently India is the
world’s fourth largest wind power generator. The Indian energy sector has an installed
capacity of 32.72 GW. Today India is a major player in the global wind energy market.

“Components of Wind Energy Conversion System”.
1. How much power does the small scale wind machine generate?
a) 18 KW
b) 2 KW
c) 12 KW
d) 30 KW
View Answer
Answer: b
Explanation: These might be used on farms remote applications and other places requiring
relatively low power. The generating capacity is up to 2kW. Small scale wind machines lower
your electricity bills by 50% – 90%.
2. Which type of wind machines are used at several residence or local use?
a) Large size machines
b) Remote machines
c) Small size machines
d) Medium size machines
View Answer
Answer: d
Explanation: These wind turbines may be used to supply less than 100 kW rated capacity, to
several residences or local use. These do not require much space they can be installed on roof tops
or on some high elevated areas.
3. Which type of wind turbines produce 100 kW or greater?
a) Large machines
b) Small machines
c) Medium machines
d) Remote Machines
View Answer
Answer: a
Explanation: Large wind turbines are those of 100 kW rated capacity or greater. They are used to
generate power for distribution in central power grids. They can have single generator at a single
site or multiple generators sited at several places over an area.
4. Which part of the wind mill acts as a housing for the turbine?
a) Wind Vane
b) Shaft
c) Wind mill head
d) Turbine
View Answer
Answer: c
Explanation: The wind mill head supports the rotor, housing, and rotor bearings. It also has control
mechanism like changing the pitch of the blades for safety devices, tail vane to orient the rotor to
face the wind. Its body is the size of the mini bus.
5. A rotor installed in a fixed orientation with the swept area perpendicular to the pre dominate wind
direction is called
a) Nacelle
b) Yaw fixed machines
c) Blades

d) Anemometer
View Answer
Answer: b
Explanation: In the locations with the prevailing wind in one direction, the design of a turbine can
be greatly simplified. The rotor can be installed in a fixed orientation with the swept area
perpendicular to the pre dominate wind direction. This machine is called yaw fixed.
6. How is the action of yaw controlled in small turbines?
a) Tail vane
b) Blades
c) Shaft
d) Yaw motor
View Answer
Answer: a
Explanation: In small turbines, yaw action is controlled by a tail vane while is larger machines a
servomechanism operated by a wind-direction sensor controls the yaw motor keeping the turbine
properly oriented.
7. Which part of the wind turbines senses wind speed, wind direction, shaft speed and torque?
a) Turbine blade
b) Shaft
c) Rotor
d) Controller
View Answer
Answer: d
Explanation: The controller senses wind speed, wind direction, shafts speeds and torques, output
power and generator temperature, Control signals are generated with the electrical output
corresponding to the wind energy input.
8. Which type of wind turbine has low RPM?
a) Small wind turbine
b) Large wind turbine
c) Medium wind turbine
d) Remote wind turbine
View Answer
Answer: b
Explanation: The rate of rotation of large wind turbine generators operating at rated capacity or
below is controlled by varying the pitch of the rotor blades. It has low rpm, about 40 to 50. It is
necessary to increase greatly the low rotor rate of turning using transmission mechanism.
9. Why recommendation of fixed ratio gears done for top mounted equipment?
a) Because they are easy install
b) Requires less space
c) Due to its low cost
d) Because of their high efficiency
View Answer
Answer: d
Explanation: Fixed ratio gears are recommended for top mounted equipment because of their high
efficiency, and minimum system risk. For bottom mounted equipment requiring a right angle drive
transmission costs can be reduced on the hub by increasing rotor speed to generator.
10. Which type of generator are made use in wind turbines?
a) Recreational generators
b) Synchronous generator

c) Asynchronous generator
d) Alternator
View Answer
Answer: b
Explanation: Generators may be either constant or variable speed type. Variable speed units are
expensive and/or unproved. Constant speed generator in use are synchronous induction and
permanent magnet types. Synchronous unit is used for large aero generator systems. It is very
versatile and has an extensive data base.
11. In which part do we find sensors and actuators?
a) Fixed gears
b) Turbines
c) Control systems
d) Blades
View Answer
Answer: c
Explanation: Control systems involves sensors and actuators. The modern large wind turbine
generator requires a versatile and reliable control system. A control system is used for i) changing
the orientation of the rotor into the wind. ii) Start up and cut-in of the equipment. iii) Power
control of the rotor by varying the pitch of the blades.
12. How many types of supporting tower for wind mill are generally used?
a) 2
b) 4
c) 3
d) 5
View Answer
Answer: b
Explanation: Four types of generating tower are used generally:
i) The reinforced concrete tower
ii) The pole tower
iii) The built up shell tube tower
iv) The truss tower.
13. On what does the selection of supporting structure depends?
a) Length of blades
b) Rotating capacity
c) Capacity of generator
d) Transmission systems
View Answer
Answer: d
Explanation: The type of the supporting structure and its height is related to cost and the
transmission system incorporated. Horizontal axis wind turbines are mounted on towers so as to be
above the level of turbulence and other ground related effects.
14. At what type of location vibrations are more in the wind turbine?
a) Downwind location
b) Up wind location
c) Windward
d) Leeward
View Answer
Answer: b
Explanation: In the upwind location (i.e. the wind encounters the turbine before reaching the

i
i
i
tower), the wake of the passing rotor blades causes repeated changes in the wind forces on the
wind forces on the tower. Due to this the tower may vibrate and may eventually be damaged.
15. At what type of location vibrations are less in the wind turbines?
a) Windward
b) Leeward
c) Downwind location
d) Upwind Location
View Answer
Answer: c
Explanation: If the turbine is downwind from the tower, vibrations are less but the blades are
subjected to severe alternating forces as they pass through the tower wake. Downwind rotors are
generally preferred for large aero generators.
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Velocity
and Power from Wind”.
1. Select the formula for total power pt?
a) Pt = 1/2gc ρAV3
b) Pt = ρAV3
D3
c) Pt = 12gc V3
D3
d) Pt = 2gcVi3
View Answer
Answer: a
Explanation:
2. Why blade velocity of wind turbine varies?
a) Due to varying wind speeds
b) Long length of blades
c) Due to the height of mount
d) Because of hotness of Sun
View Answer
Answer: b
Explanation: Wind turbine experiences change in velocity dependent upon the blade inlet angle
and the blade velocity. Since the blades are long, the blade velocity varies with the radius to a
greater degree than steam or gas-turbine blades and the blades are therefore twisted.
3. When was the Hall a day wind mill introduced?
a) 1920
b) 1923
c) 1854

d) 1864
View Answer
Answer: c
Explanation: Invented by Daniel Halladay in 1854, the Halladay Standard was the first
commercially successful self-governing windmill in 1854 was the firms of Halladay, McCray &
Co., Ellington, Conn. Partners in the company were inventor Daniel Halladay, John Burnham and
Henry McCray.
4. How much ideal efficiency should practical turbine have?
a) 10 – 12%
b) 18 – 25%
c) 80 – 90%
d) 50 – 70%
View Answer
Answer: d
Explanation: As wind turbine wheel cannot be completely closed, and because of spillage and
other effects, practical turbines have 50 to 70% of the ideal efficiency. The real efficiency η is the
product of this and ηmax and is the ratio of an actual to total power.
P = ηPtot.
5. How many types are acting on propeller type wind mill?
a) 2
b) 3
c) 4
d) 5
View Answer
Answer: a
Explanation: There are two types of forces operating on the blades of a propeller type wind
turbine. They are the circumferential forces in the direction of wheel rotation that provide the
torque and the axial forces in the direction of the wind stream that provide an axial thrust that must
be counteracted by proper mechanical design.
6. Calculate the air density, when 10m/s wind is at 1std atmospheric pressure and 15o
C?
a) 1.226 kg/m3
b) 1.033 kg/m3
c) 2.108 kg/m3
d) 0.922 kg/m3
View Answer
Answer: a
Explanation: For air, gas constant R = 287 J/kgK, 1atm = 1.01325 X 105
Pa
Air density, ρ = P/RT = (1.01325 ×105
)/(287(15+273.15)) = 1.226 kg/m3
.
7. Calculate the air density when 18m/s wind is at 1std atmospheric pressure and 34o
C?
a) 1.149 kg/m3
b) 1.9 kg/m3
c) 2.88 kg/m3
d) 5.89 kg/m3
View Answer
Answer: a
Pa
Air density, ρ = P/RT = (1.01325 × 105
)/(287(34+273.15)) = 1.149 kg/m3
.
8. What is the total power produced if the turbine diameter is 120m?
a) 0.277 KW

b) 1.224 KW
c) 4.28 KW
d) 0.89 KW
View Answer
Answer: a
Explanation: Total power P,
P = 0.245 X (πD2
/4)
= 0.245 X (π (120)2
/4)
= 0.277 KW.
a) 0.155KW
b) 0.982 KW
c) 1.452 KW
d) 3.12 KW
View Answer
Answer: a
P = 0.245 X (πD2
/4)
= 0.245 X (π (90)2
/4)
= 0.155KW.
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Wind
Turbine Operation”.
1. What is the inherent weakness of all wind machines?
a) Their efficiencies
b) Requires powerful winds to make fan rotate
c) Their dependency on the wind speed
d) Cannot be easily repaired
View Answer
Answer: c
Explanation: An inherent weakness of all wind machines are the strong dependence of the power
produced on wheel diameter and wind speed, being proportional to turbine wheel area, i.e. to the
square of its diameter and to the cube of wind velocity.
2. Why severe fluctuations in power are always undesirable in windmill?
a) Because they pose power oscillations problems
b) Damage of parts due to fluctuations
c) The efficiency of the plant will be reduced
d) Results in damage to the whole plant
View Answer
Answer: a
Explanation: Severe fluctuations in power are always undesirable, because they pose power
oscillation problems on the grid and severe strains on the windmill hardware. From an economic
point of view, a windmill is designed to produce a rated power output corresponding to maximum,
or near maximum, prevailing wind velocity at a given site would generate low powers, with full
capacity of the turbine and electric generator unused much of time.
3. Maintenance of constant output at all wind speeds above rating is called
a) Numeric rating scale
b) Tenancy

c) Flat Rating
d) TRP
View Answer
Answer: c
Explanation: More cost-effective design to a wind mill to produce rated power at less than the
maximum prevailing wind velocity, using a smaller turbine and generator and to maintain a
constant output at all wind speeds above rating. This is called flat rating.
4. A wind turbine designed too to come into operation at a minimum wind speed is called
a) Cut in velocity
b) Windward
c) Cut out velocity
d) Upwind location
View Answer
Answer: a
Explanation: Due to several loss in efficiency and power at low wind velocities, a wind turbine is
designed to come into operation at a minimum wind speed called the cut in velocity. Thus the
wind turbine operates with variable load over a narrow range between cut in.
5. Why is wind turbine designed to stop operation at cut out velocity?
a) To protect wheel against damage
b) To make a quick stop in emergencies
c) To improve the efficiency
d) In order to adjust the blades to wind direction
View Answer
Answer: a
Explanation: To protect the turbine wheel against damage at very high wind velocities, it is
designed to stop operation (such as feathering the blades) at cut out velocity. Thus the wind
turbine operates at rated velocities and at constant power between the rated and cut out velocities
and ceases the operation above the cut out velocity.
6. The fraction of time during a given period that the turbine is actually on line is called?
a) Availability factor
b) Flat rating
c) Cut in velocity
d) Cut out velocity
View Answer
Answer: a
Explanation: The availability factor is defined as the fraction of time during a given period that the
turbine is actually on line. The actual wind velocity at the propeller hub that determines the turbine
power is usually higher.
7. Over load factor is also called as
a) availability factor
b) plant operating factor
c) flat rating
d) cut out velocity
View Answer
Answer: a
Explanation: The overall load factor, also called the plant operating factor and the plant capacity
factor is the ratio of the total energy generated during a given period of time to the total rated
generation capacity during the same period.

8. How many of windmills are there?
a) 2
b) 3
c) 4
d) 5
View Answer
Answer: a
Explanation: There are two classes of windmill, horizontal axis and vertical axis. The vertical axis
design was popular during the early development of the windmill. However, its inefficiency of
operation let to the development of numerous horizontal axis designs.
9. Name the windmill which has four blades mounted on a central post.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: a
Explanation: The post mill has blades mounted on a central post. The horizontal shaft of the blade
is connected to a large break wheel. The break wheel interacts with a gear system, called the
wallower, which rotates a central, vertical shaft. This motion can then be used to power water
pumping or grain grinding activities.
10. Name the type of windmill which consists of a sloping, horizontally weather boarded or thatched
tower.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: b
Explanation: The smock mill is a type of windmill that consists of a sloping, horizontally weather
boarded or thatched tower, usually with six or eight sides. It is topped with a roof or cap that
rotates to bring the sails into the wind. It is similar to post mill. It is named so because of its
appearance.
11. Which are further improvements on smock mill?
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: c
Explanation: Tower mills are further improvements on smock mills. They have a rotating cap and
permanent body, but this body is made of brick or stone. This fact makes it possible for the towers
to be rounded. A round structure of it allows for large and taller towers.
12. Which type of windmills are been used for primary purposes?
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer

Answer: d
Explanation: The fan type windmill is specifically made for individuals. It is much smaller and
used primarily for pumping water. It consists of a fixed tower (mast), a wheel and tail assembly
(fan), a head assembly, and a pump.
This set of Energy Engineering Multiple Choice Questions & Answers
(MCQs) focuses on “Horizontal Axis Wind Mill”.
1. In which of the following, does machine rotor drives through a step up gear box?
a) Horizontal axis with two aerodynamic blades
b) Horizontal axis propeller type wind mill
c) Horizontal axis multi bladed type wind mill
d) Sail type wind mill
View Answer
Answer: a
Explanation: In horizontal axis with two aerodynamic type windmill the machine rotor drives
through a step up gear box. The blade rotor is designed to orient downwind of the tower. The
components are mounted on bed plate which is attached on a pintle at the top of the tower.
2. The rotor blades are continuously flexed by unsteady aerodynamic gravitational and inertia loads.
a) True
b) False
View Answer
Answer: a
Explanation: The rotor blades are continuously flexed by unsteady aerodynamic gravitational and
inertia loads, when the machine is in operation. If the blades are made using metal, flexing reduces
their fatigue life.
3. Which type of the following consists of single blade?
View Answer
Answer: b
Explanation: Horizontal axis propeller type wind mill consists of a long blade mounted on a rigid
hub, induction generator and gear box. If extremely long blades are mounted on rigid hub, large
blade root bending moments occur due to tower shadow, gravity and sudden shifts in wind
directions.
4. Which windmill blades are made by an array of wooden slats?
d) Horizontal axis wind mill Dutch type
View Answer
Answer: d
Explanation: Dutch type wind mill is one of the oldest wind mills in designs. The blade surfaces
are made from an array of wooden slats which rotates at high wind speeds. These types of wind
mill are cheap to build since the wood is made use of to build.
5. Which type of windmill blades are made out of sheet metal or aluminum?

View Answer
Answer: c
Explanation: Horizontal axis multi blade windmill is made from sheet metal or aluminum. The
rotors have high strength to weight ratios. They have good power coefficient, high starting torque
and added advantages of simplicity and low cost.
6. Which type of wind mills blade are made out of cloth?
View Answer
Answer: d
Explanation: The blade surface of sail type wind mill is made of cloth, nylon or plastics arranged
as mast and pole or sail wings. There is also variation in the number of sails used. Sails are found
in different designs, from primitive common sails to the advances patent sails.
7. Which type of windmill has better performance?
a) Vertical type wind mills
b) Darrieus type machines
c) Magnus effect rotor
d) Horizontal type windmills
View Answer
Answer: d
Explanation: The horizontal axis mills generally have netter performance. They have been used for
various applications including electric power generation, and pumping water. The latter introduces
some complexity into the design as the mechanical energy has to be transmitted over a distance.
8. What does TSR stand for in design consideration of wind mills?
a) Tip speed ratio
b) Torque-synchronous ratio
c) Tip suspension ratio
d) Temporary speed restriction
View Answer
Answer: a
Explanation: The tip speed ratio, X, or TSR for wind turbines is the ratio between the tangential
speed of the tip of a blade and the actual speed of the wind. The tip speed ratio is related to
efficiency, with the optimum varying with blade design.
9. With upto how many propellers can windmills are built?
a) 4
b) 2
c) 7
d) 6
View Answer
Answer: d
Explanation: Wind turbines have been built with upto six propellers type blades but two and three
bladed propellers are most common. A one bladed rotor with a balancing counter weight has some
advantages, including lower weight and cost and simpler controls, over the multi-bladed type.

10. Turbines with how many propellers are used in order to avoid vibrations?
a) 1
b) 2
c) 3
d) 4
View Answer
Answer: c
Explanation: Turbines with three blades are used to avoid vibrations that occur due to the turning
or yawing of the rotor in order to face in into the wind. However, this problem can be overcome by
controlling the yaw rate.
11. What type of cross sections does wind turbine blades have?
a) Penta hedral cross section
b) Air foiled type cross section
c) Radar cross section
d) Turbo cross section
View Answer
Answer: b
Explanation: Wind turbine blades have an air foiled type of cross section and a variable pitch.
They are slightly twisted from the outer tip to the root in order to reduce the tendency for the rotor
to stall. The blades can also have constant chord length.
12. What does WECS stands for?
a) Wind energy conversion system
b) Wind engine control system
c) Wind energy combined system
d) Wind engine comparison system
View Answer
Answer: a
Explanation: A wind energy conversion system (WECS), or wind energy harvester is a machine
that, powered by the energy of the wind, generates mechanical energy that can be used to directly
power machinery or to power an electrical generator for making electricity.
(MCQs) focuses on “Wind Turbine Operation”.
View Answer
Answer: c

View Answer
Answer: a
b) Tenancy
c) Flat Rating
d) TRP
View Answer
Answer: c
a) Cut in velocity
b) Windward
c) Cut out velocity
d) Upwind location
View Answer
Answer: a
View Answer
Answer: a
b) Flat rating
c) Cut in velocity
d) Cut out velocity
View Answer
Answer: a

c) flat rating
d) cut out velocity
View Answer
Answer: a
a) 2
b) 3
c) 4
d) 5
View Answer
Answer: a
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: a
tower.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: b
appearance.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer

Answer: c
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: d
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on
“Horizontal Axis Wind Mill”.
View Answer
Answer: a
a) True
b) False
View Answer
Answer: a
their fatigue life.
View Answer
Answer: b
directions.

View Answer
Answer: d
View Answer
Answer: c
View Answer
Answer: d
View Answer
Answer: d
a) Tip speed ratio
View Answer
Answer: a

a) 4
b) 2
c) 7
d) 6
View Answer
Answer: d
a) 1
b) 2
c) 3
d) 4
View Answer
Answer: c
View Answer
Answer: b
View Answer
Answer: a
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Vertical
Axis Wind Mill”.
1. In which wind measuring device a tubular piece of thin flexible fabric hanged vertically to
determine direction?
a) Wind socks
b) Weather vane
c) Pin wheels

d) Anemometers
View Answer
Answer: a
Explanation: Wind sock is a very basic device that measure wind direction and provide a rough
idea of the wind’s intensity. A wind sock is a tubular piece of fabric or thin, flexible fabric
attached to a pole. When there is no wind, the fabric hangs vertically from the attached pole.
2. A device which is used as device for showing direction wind as well used as a decorative purpose?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: b
Explanation: A weather vane works similarly to wind sock. Instead of a tubular sock, the weather
vane is made by placing a horizontal pole at the top of vertical pole. The poles are joined together
so that the horizontal pole has a flattened, vertical end that reacts to wind.
3. Which is the wind direction showing device that spins perpendicularly?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: c
Explanation: A pinwheel is a windmill-style turbine that spins perpendicularly to the wind
affecting it. Like wind socks and weather vanes, a pinwheel can be attached to a rotating base.
This allows the pinwheel to change direction with the wind, and it will spin facing into the
oncoming wind.
4. Which is the device that measures wind direction and its intensity?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: d
Explanation: An anemometer is any device that measures wind direction and intensity. It may be
simple, such as the devices described above, or it may be a complex, computer-aided machine that
measures and records wind patterns over time. More advanced anemometer machines are used to
aid in professional weather reporting and air traffic control.
5. What units does the anemometer measure in?
a) Feet per minute
b) Liters per minute
c) Centimeters per minute
d) Meter per seconds
View Answer
Answer: a
Explanation: The anemometer measures in feet per minute, or FPM. The rotation is sensed by a
magnetic or optical sensor that converts the signal to FPM measurement. An arrow on the vane
head identifies the direction the airflow must travel through the vane to obtain proper
measurements.

6. Which of the following type of turbine or the rotor requires relatively low velocity winds for
operation?
a) Cup anemometer
b) Savonius rotor
c) Darrieus type rotor
d) Magnus effect rotor
View Answer
Answer: b
Explanation: Savonius rotor is a simple WEC system which woks like a cup anemometer. This
type was invented by S.J. Savonius in the year 1920. It requires relatively low velocity winds for
operation. It consists of two half cylinders facing opposite directions forming as S-shaped cross
section.
7. Which type of axis does a Savonius Rotor has?
a) Horizontal axis
b) Mediolateral axis
c) Vertical axis
d) Lateral Axis
View Answer
Answer: c
Explanation: A Savonius wind energy conversion system has a vertical axis and hence eliminates
the expensive power transmission system from the rotor to the axis. Since it is a vertical axis
machine it does not matter much about the wind direction.
8. Why is Savonius rotor not suitable for installation?
a) Because of long drive shaft
b) Because of its low capacity motor
c) Because of its typical blade design
d) Due to the light material it is made of
View Answer
Answer: a
Explanation: Savonius rotor is not useful for very high installation because of long drive shaft
problems. Bracing of the topmost bearing above the rotor of a very tall vertical axis machine is
difficult requiring very long guy wires.
9. When was the Darrieus type machine invented?
a) 1925
b) 1932
c) 1929
d) 1948
View Answer
Answer: a
Explanation: Darrieus type machine was invented originally and patented in 1925 by G.J.M >
Darrieus, a French engineer. The Darrieus wind mill is a vertical axis machine that has the same
advantage of a modern rapidly rotating propeller type windmill, by use of an efficient airfoil,
effectively intercepts large area of wind with a small blade area.
10. What form of force acts on the blades of Darrieus machine?
a) Pure tension
b) Compression
c) Shear force
d) Air resistance force
View Answer

Answer: a
Explanation: Darrieus wind mill has two or three thin, curved blades with airfoil cross section and
constant chord length. Both ends of blades are attached to a vertical shaft. Thus the force in the
blade due to rotation is pure tension.
11. Which type of vertical wind machine has relatively low solidity and low starting torques?
a) Cup anemometer
b) Savonius rotor
View Answer
Answer: c
Explanation: Darrieus type rotors are lift devices characterized by curved blades with air foil cross
sections. They have relatively low solidity and low starting torques, but high tip to wind speeds
and therefore relatively high power outputs per given rotor weight and cost.
12. Which type of vertical wind machine consists of spinning cylinders?
a) Cup anemometer
b) Savonius rotor
View Answer
Answer: d
Explanation: Magnus effect rotor concept was first demonstrated by Magnus in 1912. It consists of
spinning cylinders. When cylinders spun in wind stream, translational forces are produced
perpendicular to the wind stream by the Magnus effect. Such a device can be used to propel ships
or land vehicles.
13. Aero turbine is the fraction of power in the wind through the swept area which is converted into
useful mechanical shaft power is called
a) Coefficient of performance
b) Coefficient of variation
c) Coefficient of lift
d) Coefficient of spin
View Answer
Answer: a
Explanation: The coefficient of performance of an aero turbine is the fraction of power in the wind
through the swept area which is converted into useful mechanical shaft power. Cp for horizontal
axis wind machine has theoretical maximum value = 0.593.
1-The amount of energy available in the wind at any instant is proportional to of the wind
speed.
(A) Square root power of two
(B) Square root power of three
(C) Square power
(D) Cube power
2-Wind energy is harnessed as energy with the help of windmill or turbine.
(A) Mechanical

(B) Solar
(C) Electrical
(D) Heat
3-Winds having following speed are suitable to operate wind turbines.
(A) 5 – 25m/s
(B) 10 – 35m/s
(C) 20 – 45m/s
(D) 30 – 55m/s
4-The following is (are) the classification of winds
(A) Global wind
(B) Local wind
(C) Both (A) and (B)
(D) None of the above
5-Global Cold wind move from
(A) Polar to equatorial region
(B) Equatorial to polar region
(C) Equatorial to oceanic region
(D) Oceanic to Equatorial region
6-Global Cold wind generated from Oceans moves to
(A) Mountains
(B) Equator
(C) Plain areas
(D) Poles
7- force is responsible for forcing the global winds towards westernly direction.
(A) Coriolis
(B) Gravitational
(C) Centripetal
(D) Centrifugal
8-Global winds towards westernly direction are known as
(A) Trade winds

(B) Western winds
(C) Eastern winds
9-Uneven heating occurs on land surface and water bodies are due to
(A) Air Currents
(B) Solar radiation
(C) Lunar eclipse
10- The following factor(s) affects the distribution of wind energy
(A) Mountain chains
(B) The hills, trees and buildings
(C) Frictional effect of the surface
(D) All of the above
11- The wind intensity can be described by
(A) Reynolds number
(B) Mach number
(C) Beaufort number
(D) Froude number
ANSWERS:
1-(D), 2-(A), 3-(A), 4-(C), 5-(A), 6-(C), 7-(A), 8-(A), 9-(B), 10-(D), 11-(C)
12- The wind speed is measured using an instrument called
(A) Pyranometer
(B) Manometer
(C) Anemometer
(D) Wind vane
13- The rate of change of wind speed with height is called
(A) Wind shear
(B) Wind rose
(C) Wind solidity

14- At gradient height the shear force is
(A) Zero
(B) Minimum
(C) Maximum
15-The gradient height is about m from the ground.
(A) 500
(B) 1000
(C) 1500
(D) 2000
16-The atmosphere with uniform wind speed is called the atmosphere
(A) Plain
(B) Surface
(C) Free
(D) Shear
17- Surface layer is the air layer considered from the height of local obstruction to a
height of about
(A) 50m
(B) 100m
(C) 150m
(D) 200m
18- Air layer from 100m that extends up to the gradient height is known as
(A) Surface layer
(B) Ekman layer
(C) Boundary layer
19- Low solidity rotors use which of the following force for rotation

(A) Drag
(B) Lift
(C) Centrifugal
(D) Centripetal
20- The following is the tangential velocity of the blade due to the rotation of blade.
(A) Wind velocity
(B) Incident wind velocity
(C) Blade linear velocity
(D) Relative velocity
21- Turbines blades have type cross section to extract energy from wind.
(A) Aerofoil
(B) Elliptical
(C) Rectangular
22- The Nacelle of windmill houses
(A) Gearbox
(B) Brakes
(C) Generator
ANSWERS:
12-(C), 13-(A), 14-(A), 15-(D), 16-(C), 17-(B), 18-(B), 19-(B), 20-(C), 21-(A), 22-(D)

Module-III
Biomass Power
Biomass includes all the living or dead organic materials like wastes and residues.
The animal and plant wastes and their residues are regarded as biomass. In
addition to this the products originate from the conversion processes like paper,
cellulose, organic residues for food industry and organic wastes from houses and
industries are in this category.
Origin of Bio-mass: *
Animals feed on plants and plants grew up through the photosynthesis process
using solar energy. Thus photosynthesis process is primarily responsible for
generation of biomass energy. A small portion of solar radiation is captured and
stored in plants during photosynthesis process. Therefore biomass energy is an
indirect form of solar energy.
* To use biomass energy, the initial biomass may be transformed by chemical or
biological processes to produce more convenient intermediate bio-fuels such as
methane, producer gas, ethanol and charcoal. On combustion it reacts with
oxygen to release heat.
*In nature bio-mass is formed by the process of photosynthesis of inorganic
materials.
With the help of the solar radiation in the visible region (0.4-0.8 µm), the coloured
material molecules (mainly chlorophyll) split water in organic cells (photolysis).
The originating hydrogen along with carbon dioxide forms the biomass. During
this process molecular oxygen is released into the air. The production of bio-mass
can be understood by the following equation.

The energy obtained from biomass is known as biomass energy.
Animals feed on plants and plants grow through photosynthesis process using
solar energy. Thus, photosynthesis process is primarily responsible for
generation of biomass energy.
A small portion of the solar radiation is captured and stored in the plants during
photosynthesis process. Therefore, it is an indirect form of solar energy. The
average efficiency of photosynthetic conversion of solar energy into biomass
energy is estimated to be 0.5–1.0 per cent.
To use biomass energy, the initial biomass may be transformed by chemical or
biological processes to produce more convenient intermediate bio-fuels such as
methane, producer gas, ethanol and charcoal etc. On combustion it reacts with
oxygen to release heat, but the elements of the material should be available for
recycling in natural ecological or agricultural processes. Thus the use of
industrial bio-fuels, when linked carefully to natural ecological cycle, may be
nonpolluting and sustainable. For the biomass to be considered as renewable,
growth must at least keep pace with its use. It is disastrous that forest and
firewood consumption is significantly outpacing their growth in ever-increasing
areas of the world. It is estimated that the biomass, which is 90 per cent in
trees, is equivalent to the current proven extractable fossil fuel reserves in the
world. The dry matter mass of biological material cycling in biosphere
is about 250 × 109
tons/year. The associated energy bound in photosynthesis is

2 × 1021
J/year (equivalent to continuous flow of 0.7 × 1014
W) [49].
Biomass, mainly in the form of wood, is mankind’s oldest form of energy. It has
traditionally been used both in domestic as well as industrial activities, basically
by direct combustion. However, it still plays a significant role in the supply of
primary energy in many countries of the world.
Main advantages of biomass energy are:
• it is a renewable source;
• the energy storage is its in-built feature;
• it is indigenous source requiring little or no foreign exchange;
the forestry and agricultural industries that supply feed stocks also provide
substantial economic development opportunities in rural areas;
• the pollutant emissions from combustion of biomass are usually lower than
those from fossil fuels;
• commercial use of biomass may avoid or reduce the problems of waste
disposal in other industries, particularly municipal solid waste in urban
centers;
• use of biogas plants apart from supplying clean gas, also leads to improved
sanitation, better hygienic conditions in rural areas as the harmful decaying
biomass gets stabilized;
• the nitrogen-rich bio-digested slurry and sludge from biogas plant serves as
a very good soil conditioner and improves the fertility of the soil;
• varying capacity can be installed; any capacity can be operated, even at lower
loads;
• no seasonality.
Its main disadvantages are:
• it is a dispersed and land intensive source,
• it is often of low energy density and
• it is also labor intensive and the cost of collecting large quantities for
commercial application is significant. Most current commercial applications
of biomass energy use material that has been collected for other reasons,
such as timber and food processing residues and urban waste.
• capacity is determined by availability of biomass and not suitable for varying
loads
• not feasible to set up at all locations
Manifestation of Biomass: Biomass manifests itself in various forms which are
Generally present in the organism simultaneously.
These are shown in the table below.

Table: Manifestation forms of biomass and their annual Production.
Cellulose is the most common substance in all forms of biomass. It is
polysaccharide which contains a chain of glucose molecules (C6H12O5) which are
held together in hydrogen bonds in the crystal bundle. Cellulose is not soluble in
water and other molecule solvents but reacts with alkaline and acidic solutions to
hydrate cellulose, which through formation of acids at higher temperature, can be
converted to glucose.
Hemi-cellulose is a polysaccharide which made not only of a glucose molecule
chain , but also of other sugars (C5 and C6 sugar molecules). About 20 to 40% of
the lumber type plants contain in it.
Lignin is formed in the plants through the storage of lignified plant cell
Membrane. It is soluble in soda lye (caustic soda solution) and calcium bisulphate
but not in water. Lignin offers considerable resistance to the mechanical and
enzymatic digestion of cellulose. About 30% of lumber plants contain the wood
material it.
Other materials like starch, sugar, fat, protein, chlorophyll contain very little
amount of contribution for biomass production.
Potential of Biomass: The worldwide existing biomass estimates to be about
2x1012
t = 30x1021
J = 1000billion tons of coal equivalent (land area only). Out of
these estimates, about 8x1011
= 8x1011
t/a are used for carbon fixation. The
amount of wood is estimated to be 50 to 90%. The annual growth rate of forest
(storage for biomass) also decides the amount of use of biomass and this has
been estimated around 1.5 x 1011
t = 3 x 1021
J/a = 100 billion tons COE/annum.
This amount to be 10% of the total biomass estimates.
Table:12.2 Distribution of biomass Production in the Earth’s Surface (Lith 1975).

The net primary production of biomass from the world’s forest comprises about
7% of total production of the overall world’s land area. Considering the existing
land/water distribution, 60% of the total world’s biomass production falls in
northern hemisphere and 40% in southern hemisphere.
The efficiency of biomass production can be defined as the ratio between
the calorific value of mass and necessary solar energy for the formation of
biomass.
Forests and fresh water show a large gain from solar radiation, about 0.5%
tropical forests attain a value of about 0.8%. The maximum achievable values of
some of the
biomass are:
1. Sugarcane (4.8%), 2. Maize (3.2%), 3. Sugar beat (white) (5.4%).
It is always to be taken care of that only a part of the biomass energy can be
harvested.
About 50% of the biomass (roots, leaves, etc) cannot be converted into energy.
But it is also counted that the theoretical potential of biomass energy availability
is four to six times the world’s energy consumption presently.
Energy Conversion Process:-
The conversion of biomass either in the form of heat or solid, liquid or gas
form of energy fuels. Using these individual elements in a particular process
chain, a number of bio-conversion processes can be defined which is represented
below.

Table: the elements of bio-conversion systems that may be used for a number of
Bioprocesses Conversion chain (Nairobi Conference,1981).
Raw materials in all these processes is biomass, that is available in nature either in
land or in water beds, but all is available in the form of residues or waste. Biomass
waste materials cannot be used as food or for wood production like rice husk, saw
dust and animal waste, etc. The biomass waste material (like straws, twigs, stem
pieces may also be used for bio-conversion). These waste materials are also used
for fertilizer on the earth.
From the table, it is observed that there are four forms of biomass that gets
converted into useful energy forms by several processes of biomass energy
conversion into useful products.
Table: Bio-conversion process, Raw material, End-product and Conversion
Efficiencies.

Physical Methods of Bioconversion:-
Mechanical compression of combustible materials:-
The simplest form of physical conversion of biomass is through compression of
combustible material. Its density is increased by reducing the volume by
compression through the processes called briquetting, cobs or pelletization. The
end products are called briquettes, cobs or pelletization.
The mechanical compression of combustible materials simultaneously leads to
drying of the product. There is not any uniform standardization of the end
products exist. Generally the compressed biomass or pellets contain 15-18% of
moisture.

Some characteristics parameters of compressed products are shown in the table
below.
The whole mechanical conversion of biomass includes collection, processing,
drying etc.; which requires total energy of 10 to 15% of the respective calorific
values. So the net conversion efficiency of biomass compression process lies
between 85% and 90%.
Table: Parameters of compressed biomass (Wieneke 1983)
Extraction of oil from plant products:The
extraction of energy source from biomass consists of hot press or cold press,
steam extraction or acid reduction etc. Some plants produce acid free
hydrocarbons like cellulose and lignin. The acid free hydrocarbons can be
converted into oil which can be treated as an oil. Vegetable oils are mainly edible
oils along with their use in paints, soaps and cosmetic articles.
* In Europe, the main investigation on rapeseed oil have been made. The
following outcomes are obtained:
(1) Rapeseed oil is a suitable power source for diesel engine and its efficiency is
almost similar.
(2) A mixture of rapeseed oil and diesel fuel in the ratio 1:1, leads to resinification
and carbon deposition in the engine.
(3) Emulsion of 40% oil, 40% diesel, 19% water and 1% gives good combustion in
the engine and almost no deposition. However there are small problems like cold
start of the engine due to higher viscosity.
* Bio-fuel development in India is the extraction of oil from Jatropha plant seeds.
This bio-fuel contains 40% oil which is the quality of a rich oil. This oil has served
as a replacement of bio-diesel for long decades in India. It can be used directly
after extraction in generators and diesel engines. It has the potential to provide

economic benefits at the local level since with proper management, it has the
potential to grow in dry marginal non-agricultural lands.
* One of the most productive oil plants in African soil is the palm oil. After simple
treatment this oil has capability to produce low viscosity oil which can be used as
diesel fuel. The advantages of using palm oil are: (1) it does not require any
distillation, (ii) it shows small volumes (no water), (iii) continuous harvesting is
possible.
* Another African extracted oil named as African milk bush which grows very fast
and can be harvested several times a year.
* In the forest of South America, the famous Copaiba tree is available from which
oil is extracted and used directly as fuel without any processing. The test values
for the yield lie between 40 to 60 l/a per tree.
Thermo-Chemical Conversion Processes: In thermo-chemical processes, the
biomass is either converted into heat through the process of oxidation or it is
converted into a secondary form like producer gas by some chemical processing.
One can roughly distinguish three different classes of thermochemical reactions:
(1) Combustion, (2) Gasification, and (3) Liquefaction.
These three processes may run parallel or one after another.
A. Combustion:
One of the thermo-chemical method of bioconversion is combustion. The
main biomass which has been used over the years for combustion is wood. Now
50% of the world are using wood for combustion. Especially in developing
countries wood, dung and agricultural wastes e.g. straw, stem etc. are burned.
In the combustion process of biomass (CkHmOn), the products produced are
carbon dioxide, water vapor and ash. If it comes in contact with sulphur, then SO2
is formed. Amount of energy (calorific value) released is equivalent to the burning
of dryness fraction (x) portion of mass of fuel and rest (1-x) fraction is utilized for
water evaporation process. The calorific value of moist biomass can therefore can
be written as:

Table: Calorific values of dry and moist biomasses:

Fig: Combustion temperature and relative wood consumption as a function of
moisture content (ECO 1980)
The combustion temperature decreases with increasing moisture content and the
relative wood Consumption increases for generating the same amount of heat
energy. For many combustion process, the wood containing moisture is heated in
a pre-combustion chamber so that moisture is removed from the fuel. The heated
fuel is burnt in second combustion chamber.
B. Biomass Gasification:
The complete and controlled combustion of biomass produces carbon dioxide,
hydrogen, carbon monoxide and traces of methane along with dust, tar and
steam vapor. If the combustion is partial (fuel-air supply is not as per the
stochiometric), the products of combustion contains carbon monoxide, hydrogen,
and other elements is known as producer gas. This producer gas is combustible.

The equipment used to produce producer gas through the process of biomass
gasification is known as gasifier.
The steam required for gasification process is obtained from wet biomass during
the first stage of combustion chamber.
Depending on the relative movement of the feedstock (biomass and air),
three different kinds of gasifiers are used: (1) Updraft gasifier (the air moves
upward through the biomass), (2) Downdraft gasifier (the air moves downward),
and (3)Cross-draft gasifier (feed of air and biomass are perpendicular to each
other).
Table: Advantage and disadvantage of various Gasifiers.
Almost all gasifiers fall under these three categories. The selection of gasifier
depends upon the following factors:
(1) Fuel, (2) its final available form, (3) its size, (4) moisture content and (5) ash
content.
(2) There are four zones in each of the gasifier. These are: (1) Drying zone, (2)
Pyrolysis
(3) zone, (3) Reduction zone, and (4) Combustion zone.
(4) Drying Zone: Drying of wet biomass takes place.
(5) Pyrolysis Zone: The products like Carbon dioxide and Acetic acid are
produced.
(6) Reduction Zone: Carbon monoxide and hydrogen are produced.

Combustion Zone: Steam and carbon-dioxide are formed.
Application: Producer gas can be used for many applications like:
(a) Direct heating,
(b) Shaft Power, and
(c) Chemical synthesis into methanol.
C. LIQUEFACTION OF BIOMASS
The liquefaction of gas takes place through three different processes:
1. Liquefaction through chemical reduction with the help of gasification medium.
2. Liquefaction through pyrolysis without any gasification medium.
3. Liquefaction through methanol synthesis and pre-gasification.
1. Liquefaction through Chemical Reduction:-
By introduction of carbon monoxide at high temperatures (2500
C to 4000
C) and
high pressure (140-280 bar), and in the presence of an adequate alkali catalyzer,
biomass can be liquefied directly. One such catalyzer is NaHCO3. The cellulose in
appropriate reduction to form an acidic substance and CO is reduced to CO2.
The cellulose must form a solution in 85% water. CO is obtained from the biomass
in the form of producer gas (gasification) containing H2 also. By hydrolysis, H2
leads to hydrolysis and eventually to liquefaction.
2. Pyrolysis:-
Pyrolysis is the destructive distillation or degasification of biomass that is
subjected to thermal splitting in the absence of air/oxygen. This is the reverse
process of gasification where heat is supplied externally to biomass contained in

cylinders,fluidized beds or drum reactors at temperatures between 300-10000
C.
The products of pyrolysis with calorific value are:
* Gas: Pyrolysis gas (10-15 MJ/m3
)
* Liquid: Pyrolysis oil (23-30 MJ/kg)
* Solid: Coke: (20-30 MJ/kg)
The efficiency of the pyrolysis process depends upon the following factors:
(i) Composition and size of the biomass
(ii) Pyrolysis temperature
(iii) Heating rate
(iv) Duration of biomass in reactor
The main product from pyrolysis is wood only. The destructive distillation of wood
produces pyrolysis oil or bio oil. The properties of the pyrolysis oil are closer to
the diesel oil or thermal oil.
Pyrolysis of biomass, domestic or municipal waste and non-biological waste
products like automobile tyres, has been of interest from the point of view of the
following:
* Manufacturing of pyrolysis oil as a liquid fuel
* Production of basic raw materials.
Pyrolysis has not been a commercial success because of the following:
* Bad quality of pyrolysis oil,
* High water content
* Highly viscous fluid
* Corrosion of containers due to high acidic contents
* Partly soluble in water.
3. Liquefaction through synthesis of Methanol: Lowest quality of fuel, methanol is

Produced catalytically from the suitable mixture of synthetic gas (CO and
H2mixtures). Methanol (CH3OH) is used as a fuel in certain engines of vehicles.
Biological Methods for Biomass Conversion:-
The biological method of conversion or the biochemical method of
conversion takes place at low temperature with the help of single cell micro-
organisms known as microbes. For this reason these methods are called
microbiological methods.
The microbiological reduction of carbon and water containing biomass usually
takes place in the absence of air in an aqueous environment. The microbiological
reduction of organic matter is also known as fermentation. Presently two
methods are of most important from the point of view of technology and energy
gain.

1. The fermentation of biomass of methane (biogas) production, and
2. The fermentation of biomass for ethanol production.
The detail discussion of these methods will be done later on this section.
Aerobic and Anaerobic Digestion: When the moist biomass comes in contact with
air, it automatically decays with the help of aerobic micro-organisms. As a result C
and H oxides into CO2 and H2O with simultaneous release of heat at temperature
of 70-900
C. In the carbon dioxide cycle, the aerobic bacteria plays an important
role. The bacteria releases CO2 and thus mineralize the bounded carbon in the
organic substance.
In anaerobic digestion the organic material is allowed to decay in absence of
oxygen. The different types of bacteria make a number of exchange processes
resulting the digestion of biomass and conversion into a mixture of methane and
carbon dioxide.
The energy obtained is much higher than of a low temperature decaying process.
There three steps in the production of methane. These are:
1. Acid production (hydrolysis) →Where the bonds are broken and acid is formed.
2. Acid reduction
3. Methane production → is formed from anaerobic bacteria
Fig: Simple scheme of an anaerobic digestion (Meinhold,980)
Step – I: (Acid production and hydrolysis):
In this hydrolysis process, the biomass like protein, fat and carbohydrates are
broken through the influence of water. The polymers (large molecules) are
reduced to monomers (basic molecules). The reaction is accelerated through
enzymes, which are separated from bacteria. The resulting products are: Fat,

Protein, Carbohydrates, Fatty acids, Amino acids, Sugar. These products are
fermented by the fermentation bacteria (bacteria which are active in this step)
leading to the formation of the following products:
Step-II (Acid Reduction):
In the second step, the alcohol and the low organic acids are fermented into the
following products through the action of acetogenic bacteria. (i) H2O, (ii) CO2,
(iii) H, (iv) Acetic acid (CH3COOH)
The final product of fermentation process is the acetic acid.
Step-III (Methane Production):
The acetic acid produced in the first and second step is converted into methane
and CO2 (biogas) through the effect of methanographic bacteria. At the end the
residual waste is rich in nitrogen and can be used as a good fertilizer. In each step
of the anaerobic digestion, a variety of bacteria are formed which cause the
decaying of the organic material and which are specialized for the reduction of
intermediate products.
Fig: Sequence of methane production from aerobic digestion of organic waste
Influencing parameters: The amount of biogas produces through anaerobic
Digestion of organic waste and also the methane content in it depends upon the
following parameters:
1. Kind of substrate, 2. Dry matter content, 3. Temperature, 4. Digestion
period,5. Mode of operation, 6. PH value.
Description of biogas Digesters: There are various types of digesters according to
the need of the situation.
But there are two basic types of distinguishable digesters according to the loading
used.
1. Batch type digester
2. Continuous flow digester.
A batch type digester is a simple digester in which organic material is filled

in a closed container and allowed to be digested an aerobically over a period of
two to six months time depending upon the feed material and other parameters
like temperature, pressure etc.
Advantage: This type of digester is very simple to run and requires very less
attention. It is easy to start and emptying out. Maximum efficiency of digestion
depends upon the carefully loading and waste of biomass.
Limitation: It has the problem of handling the waste material.
A typical miniature digester with a tank of 10 liter is shown in the figure below.
The batch digesters are suitable for fibrous waste and difficult to digest.According
to the availability of the waste, this is more suitable for irregular availability of
waste. For continuous waste supply, batch digester can be used.With increase of
digestion time.
If several batch digesters are used in series, with each at a different stage in the
digestion cycle, a continuous gas flow is obtained which is shown in the cycle. The
digesters would be started up at regular intervals, so that the continuous gas flow
is

Fig: A continuous flow of biogas from four batch digesters with a staggered
operation maintained
* Indian Institute of Science (IISc) Bangalore has developed a digester but that
shows some heat los problem.
* Indian Institute of Technology (IIT) Delhi have made attempts to utilize solar
energy systems which could be integrated with flouting or fixed dome designs
for maintaining higher slurry temperature. They have produced biogas from
rated value 0.3 m3 /day/m3 digester volume to 0.37-0.52 m3 /day/m3 (Bansal
et al, 1985).
Biogas from agro industrial residues:
The agro-industrial residues can be conventionally converted into biomass
production with suitable mixed digesters. The Commonwealth Scientific and
Industrial Research Organization (CSIRO) in Australia tested various fruit
processing waste in 23 m3 pilot digester. This is completely mixed through
biogas recirculation.
1. Thermophilic Digestion: Most of the biogas digesters produce biogas due to
action of bacteria known
As mesophilic bacteria. These type of bacteria needs 350 C but biogas can also be
produced due to some of the other bacterias which need temperature around
of 500 C.
The advantages of this thermophilic digestion includes:-
1. Shorter retention times,
2. Increased digestion efficiency,
3. and increased destruction of pathogens.
The disadvantages include:-
1. Greater sensitivity to temperature variation,
2. the need for better mixing,
3. and the additional energy needed for digester heating.
2. Anaerobic Contact Reactors: In this digester the feed enter near the top and is
drawn off at the bottom. The liquid flows through a setting tank where the
sludge containing methane forming micro-organisms settles out and is returned
to the digester.
3. Anaerobic Filter Reactors: It consists of a chamber filled with a packing medium;
The methane forming bacteria form a film on the large surface and are not carried
out of the digester with the effluent. For this reason, these digesters are also
known as fixed film or retained film digesters. The fluid enters at the bottom

and flows up through the packing medium; as the organisms in the liquid pass
over the bacterial film, they are converted to biogas.
Fig: Anaerobic Filter Reactor
Biogas from Human Residue:
Biogas from sewage:-
In 1949’s and 1950’s, anaerobic digestion system were used to produce heat
energy or electric power in sewage treatment in US municipalities as well as
several other countries. But it was abandoned due to the cost of energy
production is higher than the Govt. supply. Biogas is used in several states to
fuel engines and to produce electricity. Biogas provides low pressure steam for
Chicago plant and boiler fuel for a steam power plant in Los Angels. Waste heat
from biogas is supplied to New York Plant for running purposes.
Biogas heat may be utilized for generation of steam which will be utilized to
run the turbine to produce electricity.
* About 600,000 ft3 of biogas is produced from daily sewage treatment plant in
New Delhi. About 50,000 families are using as cooking gas for their use.
Biogas from Night Soil:-
Human excreta (waste) from the human body is known as night soil. These can be
used in biogas plants to produce electricity. These type power production is
quite popular in India, Nepal and China. The study has been found that night
soil from 40 to 60 people are enough to produce cooking gas for one family.
Stirring Equipment: It is desirable that the digesters are thoroughly mixed to:-
1. Avoid the formation of sink layers on the floor of the fermenter,
2. Avoid the formation of scum on the uppermost surface of the substrate
resulting in the cooking of the system,
3. Maintain a uniform temperature,

4. Maintain a uniform food stuff to the bacteria.
Usually mechanical stirring equipment is used for the mixing of the substrate.
Other equipments like circulation pump, gas compression, valve gear are also
used for Stirring.
Production of Ethanol (C2H5OH):-
Ethanol production is based on the principle of anaerobic fermentation of
sugar solutions with the help of microorganism present in the yeast. This process
is known as alcoholic fermentation. There are three types of biomass used for
ethanol production in order of increasing complexity.
1. Sugar containing biomass,
2. Starch containing biomass,
3. Cellulose containing biomass.
Table: Inputs for Ethanol production

The Fermentation Process:-
The rate of alcohol production depends upon the following factors.
1. Sugar content: (generally, 10 – 18% w.r.t. mass. Higher values will slow down
the fermentation process.)
2. Fermenting temperature: (30 – 400 C. The reaction being exothermic. At
higher temperature, there is danger of foam formation and therefore loss of
efficiency.)

3. pH value : (pH value of 4.0 or higher is required because yeast lives in the range
of 3.0 to 6.0.)
4. Yeast concentration: (In stationary condition, 40 – 60 gram of yeast used for 1
litre of substrate. Aerobic process takes place. For fermentation process, air is
allowed to flow through the fermenter to ensure the presence of yeast.)
5. Fermentation time: (Simple fermentation process requires 36 to 48 hours.
However new technology requires 1 to 5 hours. ) .
Fig: Reaction time for fermentation in a batch process (Menrad et al., 1982)

Fig: Block diagram of ethanol production from sugarcane
* At the end of the distillation, slurry remains as a waste, which is mixture of
water, organic material and minerals. This slurry can be used either as fodder
or as fertilizer. This slurry can also be used in biogas plants for biogas
production. The slurry has been combusted and the heat produced is used for
manufacturing process.
Characteristics of Ethanol:*
The calorific value of ethanol is quite lower than that of petrol.
* Since the ethanol has a lower stochiometric ratio, the calorific value of air/fuel
mix is nearly same.
* The boiling point of ethanol is same as that of petrol.
* Lower volatile nature of ethanol leads to a bad engine start in cold.
Its main disadvantages are:-
(1) It is dispersed and land-intensive source.
(2) It is often low energy density.
(3) It is also labour intensive and cost of collecting large quantities for commercial
application is significant.
(4) Capacity is determined by availability of bio-mass and not suitable for varying

loads.
(5) It is not feasible to set up at all locations.
Biomass Conversion Process:-
Multiple choice questions and answers
objective tyPe Questions
1. Storage of biomass energy is:
(a) very difficult (b) inbuilt feature
(c) expensive (d) impossible
2. Biogas is predominantly:
(a) hydrogen (b) carbon monoxide
(c) carbon dioxide (d) methane
3. Heating value of producer gas is:
(a) 4–8 MJ/m3
(b) 14–18 MJ/m3
(c) 24–28 MJ/m3
(d) 34–38 MJ/m3
4. Fluidized bed gasifier produces:
(a) low tar and high particulate (b) high tar and low particulate
(c) gas at low conversion efficiency (d) low exit temperature

5. The water content in anhydrous ethanol is:
(a) 20% (b) 10%
(c) 5% (d) 0.7%
6. The percentage of ethanol in blended petrol (gasohol) is:
(a) 20% (b) 30%
(c) 4% (d) 50%
7. Compared to petrol operated engine, an ethanol operated engine:
(a) produces 50% more power
(b) produces 20% more power
(c) produces comparable amount of power
(d) produces 20% less power
8. Increasing the pressure inside biogas plant:
(a) increases the gas production (b) decreases the gas production
(c) has no effect on gas production (d) causes explosion
9. When ambient temperature of biogas plant decreases below 20°C:
(a) the gas production increases
(b) the gas production first increases and then decreases
(c) the gas production decreases
(d) remains unaltered
10. The optimum solid concentration in a biogas is:
(a) 37–39 % (b) 27–29 %
(c) 17–19 % (d) 7–9 %
11. Which material should be added in the feed of biogas plant to increase nitrogen
content?
(a) Lignin (b) Carbohydrate
(c) Chopped leguminous plants (d) Night soil
12. Compared to fixed dome model of biogas plant a floating drum type plant is:
(a) more efficient (b) less efficient
(c) equally efficient (d) very cheap
13. In energy farming, the plantation and harvesting is planned and managed so as to:
(a) reduce manual labour (b) insure the sustainability of the resource
(c) insure multiple harvesting per year (d) minimize the cost involved
14. Bio-diesel is:
(a) obtained from fermentation of sugars

(b) obtained from pyrolysis process
(c) exudates of plants
(d) an upgraded vegetable oil
15. Liquefaction of biomass is carried out at:
(a) high temperature and low pressure
(b) relatively low temperature and high pressure
(c) relatively low temperature and normal pressure
(d) room temperature and high pressure
16. Which of the following is a biodegradable waste?
(a) Vegetable and fruit peels (b) Silver foil
(c) Detergent (d) Rubber
17. The process in which waste material is reduced to ashes is called:
(a) biodegradation (b) composting
(c) recycling (d) incineration
18. Which of the following is not a biomass?
(a) Plants and trees (b) Wood
(c) Cattle dung (d) Water
19. Which of the following fuels can be produced by fermenting sugar cane top, sawdust,
corn or wood chips?
(a) Alcohol (b) Biogas
(c) Producer gas (d) Bio-diesel
20. A small percentage of the hazardous waste is also generated in the house. Which of the
following is a hazardous waste that is generated in the house?
(a) Paper (b) Leftover foodstuff
(c) Old batteries (d) Plastic bags
21. Which of the following does not have energy at all?
(a) Protein (b) Fat
(c) Carbohydrate (d) Vitamin
22. Burning of plastics, especially PVC releases which of the following harmful gases into
the atmosphere:
(a) Lithium (b) Dioxins
(c) Methane (d) Nitrogen
23. The optimal pH value of slurry for biogas production ranges between:
(a) 6.8 and 7.2 (b) 5 and 5.6
(c) 8 and 9.5 (d) 0 and ± 0.5

24. The waste water from distillery can be used to produce which of the following gases
commercially?
(a) Carbon dioxide (b) Hydrogen
(c) Oxygen (d) Biogas
25. Gasification of biomass is which type of conversion process?
(a) Chemical (b) Biochemical
(c) Biological (d) Thermochemical
26. Hydrogen can be generated commercially through:
(a) Aerobic digestion (b) Steam reforming of methane
(c) Incineration (d) Anaerobic digestion
27. Presence of which of the following in the biogas causes corrosive effect?
(a) Hydrogen sulfide (b) Methane
(c) Carbon dioxide (d) Nitrogen
28. The gas generated through biomass gasification is called:
(a) ethane (b) biogas
(c) producer gas (d) carbon dioxide
29. Fuel reforming is a process of:
(a) transforming of fossil fuel into hydrogen
(b) transforming of fossil fuel into carbon monoxide
(c) removing carbon compounds from fossil fuel
(d) removing sulfur compounds from fossil fuel
Multiple Choice Questions and Answers
1. What is biomass?
a) Organic materials from living organisms
b) Inorganic materials from living organisms
c) Inorganic materials from non-living organisms
d) Organic materials from non-living organisms
View Answer
Answer: a
Explanation: Biomass is a term for all organic materials stemming from living organisms like
plants, animals and microorganisms. Examples of biomass are – animal waste, dead plants
and animals, sugar, fats, etc.
2. Which of the following can be classified under biomass?
a) Steel
b) Organic molecules containing hydrogen
c) NaOH

d) Iron
View Answer
Answer: b
Explanation: Organic molecules containing hydrogen is a biomass. Steel is made up of
inorganic materials. NaOH is a strong base which is made up of an inorganic material called
sodium (Na). Iron (Fe) is another inorganic material which is used for its magnetic properties.
3. Which of the following is not used as food for humans?
a) Sugars
b) Glucose
c) Cellulosic matter
d) Fats
View Answer
Answer: c
Explanation: Cellulosic biomass is not used as a food source for humans. It is made up of very
complex sugar polymers. Sugars, glucose and fats are used in various food items.
4. is an example of cellulosic biomass.
a) Glucose
b) Fats
c) Lipids
d) Agricultural residue
View Answer
Answer: d
Explanation: Agricultural residue is an example of cellulosic biomass. They generally include
leftover material from crops like stalks and leaves. Fats, lipids and glucose are not cellulosic
biomass.
5. Value of any biomass depends on properties.
a) chemical and physical
b) chemical and photo sensitive
c) physical and photo sensitive
d) the number of carbon molecules and on the number of tin molecules
View Answer
Answer: a
Explanation: The value of any biomass depends on the chemical and physical properties.
These are basically the properties of the large molecules from which it is made. It does not
depend on the light and the number of molecules.
6. Which of the following are characterizes an ideal energy crop?
a) High yield, high energy input to produce, high cost and high nutrient requirements
b) High yield, low energy input to produce, low cost and low nutrient requirements
c) High yield, high energy input to produce, low cost and high nutrient requirements
d) Low yield, high energy input to produce, high cost and high nutrient requirements
View Answer
Answer: b
Explanation: In general, the characteristics of any ideal energy crop are – high yield, low

energy input to produce, low cost, consists of least contaminants and low nutrient
requirements. These depend on the local climate and soil conditions.
7. Which energy forms can biomass be converted to?
a) Electrical and light
b) Light and chemical
c) Electrical and heat
d) Heat and light
View Answer
Answer: c
Explanation: Biomass can be converted to electrical and heat energy. It can also be used as
transport fuel and chemical feedstock. It cannot be converted to light energy.
8. The heating value is expressed in BTU/kg.
a) True
b) False
View Answer
Answer: a
Explanation: The heating value is expressed in BTU/kg. BTU stands for British Thermal Unit
and is used to measure thermal (heat) energy. It is the amount of energy needed to raise 1
pound of water 1 degree farad at sea level. Other commonly used units are MJ/kg and cal/g.
9. What does heat value indicate?
a) Amount of energy consumed by biomass to produce energy
b) Amount of energy required to process biomass to produce energy
c) Amount of energy required as heat by the organisms
d) Amount of energy that is available in the fuel
View Answer
Answer: d
Explanation: Heating value indicates the total amount of energy that is available in the fuel.
It is one of the most important characteristics of a fuel. It is mostly a function of fuel’s
chemical composition.
10. What is higher heating value?
a) Amount of energy available in the fuel + energy contained in water vapour in the exhaust
gases
b) Total amount of energy available in the fuel – energy contained in water vapour in the
exhaust gases
c) Total amount of energy available in the fuel * energy contained in water vapour in the
exhaust gases
d) Total amount of energy available in the fuel
View Answer
Answer: a
Explanation: Higher heating value is the total amount of energy available in the fuel,
including energy contained in water vapour in the exhaust gases. Heating value indicates the
total amount of energy available in the fuel.
11. What is lower heating value?
a) Amount of energy available in the fuel + energy contained in water vapour in the exhaust

gases
b) Total amount of energy available in the fuel – energy contained in water vapour in the
exhaust gases
c) Total amount of energy available in the fuel / energy contained in water vapour in the
exhaust gases
d) Total amount of energy available in the fuel which cannot be used
View Answer
Answer: b
Explanation: Lower heating value (LHV) is total amount of energy available in the fuel –
energy contained in water vapour in the exhaust gases. Generally, LHV is not an appropriate
value to use for biomass combustion.
12. High moisture fuels burn readily and provide more useful heat per unit mass.
a) True
b) False
View Answer
Answer: b
Explanation: High moisture content in fuels do not allow them to burn readily and provide
less useful heat per unit mass. This is because water itself does not provide any energy value.
In fact, much of the supplied energy is used to heat and vaporize water which leads wastage
of supplied energy.
13. Moisture content can be calculated on two bases, namely
a) light and heavy
b) weighted and even
c) wet and dry
d) light and dry
View Answer
Answer: c
Explanation: Moisture content can be calculated on two bases, namely, wet and dry.
Weighted is generally used to calculate weighted average. Light and heavy are not related to
moisture content.
14. What are the main components of cellulosic biomass?
a) Hemicellulose and lignin
b) Hemicellulose and sugars
c) Cellulose, sugars and fats
d) Cellulose, hemicellulose and lignin
View Answer
Answer: d
Explanation: The main components of cellulosic biomass are cellulose, hemicellulose and
lignin. Sugars and fats are not cellulosic biomass.
15. Biomass is seasonal.
a) True
b) False
View Answer

Answer: a
Explanation: Biomass is seasonal, especially plant biomass. This is a problem because most
biomass comes from agricultural feedstock. However, the energy and feedstock demands
are continuous irrespective of season.
1. Which of the following can be classified under solid biomass?
a) Agricultural residues
b) Waste water
c) Industrial effluents into rivers
d) Plastic
View Answer
Answer: a
Explanation: Agricultural residues can be classified under solid biomass resource. Waste
water and polluted rivers are not solids. Plastic is not a biomass.
2. What are energy crops?
a) Crops grown to remove insects
b) Crops grown to be used in generating energy
c) Crops grown to feed people
d) Crops that produce energy
View Answer
Answer: b
Explanation: Energy crops are crops that are grown with the specific intention to generate
energy. They don’t produce energy by themselves but they are used to generate energy or
serve as fuel. Eg. – bioethanol.
3. Which of the following are examples of energy crops?
a) Banyan
b) Mango
c) Herbaceous and woody
d) Apple and herbaceous
View Answer
Answer: c
Explanation: Herbaceous and woody crops are examples of energy crops. Like agricultural
crops are grown to feed, energy crops are grown specifically to be used as an energy
resource.
4. What are herbaceous crops?
a) Insecticides
b) Rice
c) Agricultural fertilizers
d) Agricultural byproducts
View Answer
Answer: d
Explanation: Herbaceous crops are plants that do not have much wood and has green and
soft stems. Generally, they are agricultural byproducts like columbine. Sometimes, crops like
potatoes are solely grown to produce energy.

5. Which of the following are examples of woody biomass?
a) Fallen trees due to natural disasters
b) Mint
c) Columbine
d) Agricultural byproducts
View Answer
6. Which of the following are examples of lipids?
a) Sugar
b) Palm oil
c) Glucose
d) Cellulose
View Answer
Answer: b
Explanation: Palm oil is an example of lipids. Other examples are soybean oil, rapeseed oil,
wax, animal fat, etc. Glucose is an example of sugar.
7. Which of the following can be used to replenish nutrients in soil?
a) Steel
b) Soda
c) Biomass ash
d) Coal ash
View Answer
Answer: c
Explanation: Biomass ash can be used as a soil amendment to help replenish nutrients. Coal
ash cannot be used for the same because it contains toxic metals. Steel and soda are not
used to replenish soil’s nutrients.
8. Which of the following is an example of short rotation coppice?
a) Maize
b) Wheat
c) Corn
d) Willow
View Answer
Answer: d
Explanation: Willow is an example of short rotation coppice (SRC). It is a forestry residue.
Corn, maize and wheat are examples of herbaceous crops.
9. Algae are used as feedstocks for bioenergy.
a) True
b) False
View Answer
Answer: a
Explanation: Algae are used as feedstocks for bioenergy. They use sunlight to create biomass
containing key components like lipids, proteins and carbohydrates. They include microalgae,
macroalgae like seaweed and cyanobacteria or blue-green algae.
10. Which of the following found in municipal waste can be used as biomass?
a) Agricultural residue

b) Kitchen waste
c) Residential garbage
d) Plastic covers
View Answer
Answer: b
Explanation: Kitchen waste can be used as a resource for biomass. Residential garbage and
plastic covers cannot be used directly. Agricultural residue is not found in municipal waste.
11. Land fill is an example of wet waste.
a) False
b) True
View Answer
Answer: b
Explanation: Land fill is an example of wet waste. It consists of residential wastes, industrial
wastes and other wastes from sewage. It also consists of manure in the form of animal
wastes.
12. wastes are used as methane boosters.
a) Agricultural
b) Forestry
c) Industrial
d) Municipal
View Answer
Answer: c
Explanation: Many industrial wastes are used as methane boosters due to their extremely
high methane potential. Agricultural, municipal and forestry wastes are not suitable for
methane boosters.
13. biomass is used for waste water treatment.
a) Agricultural
b) Industrial
c) Municipal
d) Aquatic
View Answer
Answer: d
Explanation: Aquatic biomass in the form of micro-organisms are used for waste water
treatment. They operate in anaerobic environment during the treatment.
14. Which of the following parameters is used to define sustainability of biogas feedstock?
a) Heating value
b) Calorific value
c) C:N ratio
d) Thermal voltage
View Answer
Answer: c
Explanation: Carbon to nitrogen (C:N) ratio is one of the most important parameters used to
talk about the sustainability of the biogas feedback. Heating and calorific value are
parameters to describe the available fuel in a given biomass.

15. Which of the following is not a biomass resource?
a) Animal wastes
b) Forestry residue
c) Agricultural residue
d) Sunlight
View Answer
Answer: d
Explanation: Sunlight is not a biomass resource. Animal wastes, forestry residue and
agricultural residue are biomass resources. They are used to generate energy either by
combustion or bio-chemical processes.
1. Which of the following technologies are used to convert biomass into useful energy forms?
a) Bio-chemical process
b) Galvanization
c) Doping
d) Photoelectric effect
View Answer
Answer: a
Explanation: The three main technologies used to convert biomass into useful forms of
energy are bio-chemical, thermo-chemical and physio-chemical processes. Galvanization is a
process used to prevent corrosion of metals. Doping and photoelectric effect are not related
to biomass conversion technologies.
2. What are the four main types of thermo-chemical processes?
a) Galvanization, photovoltaic effect, chemo-mechanical effect, pyrolysis
b) Pyrolysis, gasification, combustion, hydrothermal processing
c) Pyrolysis, gasification, combustion, doping
d) Photovoltaic effect, gasification, combustion, hydrothermal processing
View Answer
Answer: b
Explanation: The four main types of thermo-chemical processes are pyrolysis, gasification,
combustion and hydrothermal processing. Photovoltaic effect, doping, chemo-mechanical
effect and galvanization are not related to biomass conversion technologies.
3. What are the two primary processes under bio-chemical conversion?
a) Photosynthesis and respiration
b) Photosynthesis and photovoltaic
c) Anaerobic digestion and fermentation
d) Anaerobic digestion and photosynthesis
View Answer
Answer: c
Explanation: Anaerobic digestion and fermentation are two primary processes under bio-
chemical conversion. Photosynthesis, photovoltaic and respiration are not related to
biomass conversion technologies.
4. Which of the following is an example of physio-chemical conversion technique to convert
biomass into usable forms of energy?

a) Pyrolysis
b) Gasification
c) Anaerobic Digestion
d) Extraction with esterification
View Answer
Answer: d
Explanation: Physio-chemical process mainly consists of extraction with esterification.
Pyrolysis and gasification are thermo-chemical conversion. Anaerobic digestion is a bio-
chemical conversion process.
5. Which of the following is a product of pyrolysis of biomass?
a) Producer gas
b) Steel
c) Agricultural residue
d) Sodium
View Answer
Answer: a
Explanation: The output is producer gas. Steel and sodium are not the outputs of any
pyrolysis process. Agricultural residue is a type of biomass.
6. Pyrolysis occurs in the presence of oxygen.
a) large amounts of
b) absence of
c) extremely large amount of
d) low amounts of
View Answer
Answer: b
Explanation: In pyrolysis, the biomass is subjected to high temperatures in the absence of
oxygen. The output of pyrolysis is producer gas which is a mixture of flammable gases
(primarily CO and H2) and non-flammable gases (primarily nitrogen and carbon dioxide).
7. Which of the following best indicates the process of gasification?
a) Biomass → carbon dioxide and water → producer gas and charcoal → carbon monoxide
and hydrogen
b) Biomass → carbon monoxide and hydrogen → carbon dioxide and water → producer gas
and charcoal
c) Biomass → producer gas and charcoal → carbon dioxide and water → carbon monoxide
and hydrogen
d) Producer gas and charcoal → carbon dioxide and water → carbon monoxide and hydrogen
→ biomass
View Answer
Answer: c
Explanation: Gasification basically converts all the available biomass to “gas”. In the first
stage, the biomass is partially combusted to form producer gas and charcoal which is then
sent to the second stage. In the second stage, the carbon dioxide and water produced in the
first stage is chemically reduced by charcoal to form carbon monoxide and hydrogen.

8. Which of the following is best suited for hydrothermal processing?
a) Forestry byproducts
b) Wheat
c) Corn
d) Sewage sludge
View Answer
Answer: d
Explanation: Feedstocks with high moisture content like sewage sludge are suitable for
hydrothermal processing. Agricultural residue like wheat and corn and forestry byproducts
are not best suited for hydrothermal processing.
9. What is hydrothermal processing?
a) Heating aqueous slurries of biomass at high pressures to produce products of greater
energy density
b) Heating aqueous slurries of biomass at high temperatures to produce products of lower
energy density
c) Heating aqueous slurries of biomass at low pressures to produce products of greater
energy density
d) Heating aqueous slurries of biomass at low temperatures to produce products of lower
energy density
View Answer
Answer: a
Explanation: Hydrothermal processing is a biomass conversion technique that involves
heating of aqueous slurries of biomass at high pressures to produce products of greater
energy density. Feedstocks with high moisture content like manures are best suited for this
process.
10. What is anaerobic digestion?
a) Produces biogas by heating the biomass
b) Produces biogas using micro-organisms operating in anaerobic conditions
c) Produces biogas by subjecting the biomass to high pressures
d) Produces biogas using micro-organisms operating in aerobic conditions
View Answer
Answer: b
Explanation: Anaerobic digestion is a biological process of breaking down the biomass to
produce products with high energy density – biogas. It occurs in anaerobic conditions. Waste
water treatment plants commonly use anaerobic conditions to treat the influent.
11. Catalytic liquefaction occurs at
a) low temperature, low pressure
b) high temperature, high pressure
c) low temperature, high pressure
d) high temperature, low pressure
View Answer
Answer: c
Explanation: Catalytic liquefaction is a thermo-chemical biomass conversion process. It

requires low temperature and high pressure and the process is carried out in liquid phase
under the presence of a catalyst.
12. Sugarcane is used to produce ethanol.
a) True
b) False
View Answer
Answer: a
Explanation: One of the most commonly used feedstocks to produce ethanol is sugarcane.
This is very popular in developing due to the high productivity of sugarcane when supplied
with sufficient water.
13. Which of the following are used to produce ethanol when water is not available in plenty?
a) Sugarcane
b) Wheat
c) Corn
d) Sorghum
View Answer
Answer: d
Explanation: Cassava or sorghum is commonly used to produce ethanol when water is not
available in plenty. Sugarcane is used when there is no limitation on water content. Wheat
and corn do not produce ethanol.
14. Which of the following are commonly used in fermentation process?
a) Yeast
b) Bacteria
c) Mushrooms
d) Virus
View Answer
Answer: a
Explanation: Yeast is commonly used in fermentation process. Fermentation is the process
converting biomass to alcohol and carbon dioxide.
15. Fermentation is aerobic process.
a) True
b) False
View Answer
Answer: b
Explanation: Fermentation is an anaerobic process. It is another commonly used bio-
chemical process of converting feedstock (biomass) to energy in the presence of micro-
organisms.
1. Which of the following is a product of biomass gasification?
a) Hydrogen
b) Steel
c) Carbon (solid)
d) Iron
View Answer

Answer: a
Explanation: Biomass gasification is process that converts biomass into gases in a controlled
amount of oxygen or partial combustion. Hydrogen is a product of biomass gasification.
Steel, carbon (solid) and iron are not gases.
2. What is water-gas shift reaction?
a) Carbon dioxide + water → Carbon monoxide + Hydrogen + small heat
b) Carbon monoxide + water → Carbon dioxide + Hydrogen + small heat
c) Carbon dioxide + water + heat → Carbon monoxide + Hydrogen
d) Carbon monoxide + water + heat → Carbon dioxide + Hydrogen
View Answer
Answer: b
Explanation: carbon monoxide + water → carbon dioxide + hydrogen + small heat is the
water-gas shift reaction. It is an exothermic reaction as heat is released and not used.
3. Which of the following temperature ranges are suitable for biomass gasification?
a) Above 1000 degree Celsius
b) Between 500 and 600 degree Celsius
c) Between 700 and 1000 degree Celsius
d) Less than 500 degree Celsius
View Answer
Answer: c
Explanation: The most suitable temperature range for biomass gasification is between 700
and 1000 degree Celsius. The reactant is partially oxidized to produce a mixture of gaseous
products including hydrocarbons. Sometimes, steam is also used as gasification agents.
4. What are the three main types of gasifiers?
a) Fixed bed, hydrothermal liquefaction and carbonisation
b) Fixed bed, fluidized gasifiers and carbonisation
c) Carbonisation, liquefaction and entrained flow gasifiers
d) Fixed bed, fluidized gasifiers and entrained flow gasifiers
View Answer
Answer: d
Explanation: Fixed bed, fluidized and entrained flow gasifiers are the three main types of
gasifiers used in biomass gasification. Liquefaction and carbonisation are not gasifying
techniques.
5. Biomass is moved at a very slow rate in fixed bed gasifier.
a) True
b) False
View Answer
Answer: a
Explanation: Biomass is moved at a very slow rate in the fixed bed gasifier. Hence, it is also
called as moving bed reactor and is operated around 1000 degree Celsius.
6. How is the biomass material and gasification agent fed into an updraft gasifier?
a) Biomass from top, gasifying agent from top
b) Biomass from top, gasifying agent from bottom
c) Biomass from bottom, gasifying agent from top

d) Biomass from bottom, gasifying agent from bottom
View Answer
7. What is the contaminant in the product gas that is withdrawn from a low temperature zone
in a fixed bed gasifier?
a) Gold
b) Platinum
c) Tar
d) Nickel
View Answer
Answer: c
Explanation: The hot gas coming from the bottom dries the biomass near the top of the
vessel and provides heat for pyrolysis of the descending biomass. Along with providing heat,
it also embeds tar into it. When the product gas is removed from a low temperature zone, it
consists of tar which is a contaminant.
8. The product gas removed from the low temperature zone undergoes before being
used as fuel in combustion for electricity generator.
a) liquefaction
b) condensation
c) evaporation
d) cleaning
View Answer
Answer: d
Explanation: The product gas removed from the low temperature zone undergoes cleaning.
This is to remove contaminants like tar from the gas so that it can be used as fuel in
combustion engine for electricity generator.
9. How is the biomass material and gasification agent fed into a downdraft gasifier?
a) Biomass from top, gasifying agent from top
b) Biomass from top, gasifying agent from bottom
c) Biomass from bottom, gasifying agent from left side
d) Biomass from top, gasifying agent from right side
View Answer
Answer: a
Explanation: In a downdraft generator, the biomass and the gasifying agent is fed into the
vessel from the top. Air or oxygen is then fed into the system homogeneously at the so
called throated area.
10. The tar content of the product gas in downdraft gasifier is updraft gasifier.
a) equal to
b) less than
c) greater than
d) cleaner than
View Answer
Answer: b
Explanation: The tar content of the product gas in a downdraft gasifier is lower than updraft
gasifier. However, the particulate content of the gas is higher.

11. Which of the following applications is the product gas from downdraft gasifier suitable for?
a) Fuel for combustion engine
b) Fuel for burning wood
c) Fuel for internal combustion engine
d) Fuel for household purposes
View Answer
Answer: c
Explanation: The product gas from downdraft gasifier is suitable for applications like fuel for
internal combustion engine to generate electricity. This is because it consists of less amount
of tar and more amount of particulate matter as compared to the product gas from an
updraft gasifier.
12. Which of the following applications can the producer gas be used for?
a) Producing nickel
b) Producing copper
c) Producing glucose
d) Producing methanol
View Answer
Answer: d
Explanation: Producer gas can be used to produce methanol in an economically viable
manner. Methanol is used as fuel for heat engines as well as feedstock for industries.
13. Which of the following are keys to design a gasifier?
a) Reducing biomass to charcoal and converting charcoal at suitable temperature to produce
carbon monoxide and hydrogen
b) Oxidizing biomass to charcoal and converting charcoal at suitable temperature to produce
carbon monoxide and hydrogen
c) Reducing biomass to charcoal and converting charcoal at suitable temperature to produce
carbon dioxide and hydrogen
d) Oxidizing biomass to charcoal and converting charcoal at suitable temperature to produce
carbon dioxide and hydrogen
View Answer
Answer: a
Explanation: The key to gasifier design is to create conditions such that biomass is reduced to
charcoal and the charcoal converted to carbon monoxide and hydrogen at suitable
temperatures. It is important to note that biomass is reduced and not oxidized.
14. How does air enter and exit in a cross-draft gasifier?
a) Air enters from one of the sides and exits from the top
b) Air enters from one side and exits from the other
c) Air enters from one of the sides and exits from the bottom
d) Air enters from the bottom and exits from the top
View Answer
Answer: b
Explanation: In a cross-draft gasifier, air enters from one of the sides and exits from the
other. Cross-draft gasifiers are compactly constructed and require low maintenance.

15. Ash sticks to the side in a cross-draft gasifier.
a) True
b) False
View Answer
Answer: b
Explanation: Ash falls to the bottom in a cross-draft gasifier. The ask does not interrupt the
normal operation and hence the gasifier does not need a grate.
1. Which of the following is a substrate for biogas production?
a) Municipal and residential waste
b) E-waste
c) Metallic waste
d) Gaseous effluents
View Answer
Answer: a
Explanation: Municipal and residential waste is a good substrate for biogas production. E-
waste and metallic waste do not consist of carbon compounds. Gaseous effluents are not
used to produce biogas.
2. Which of the following is a preferred substrate for biogas production? Note that TS stands for
total solids.
a) Less than 1% TS
b) 20-40% TS
c) 1-5% TS
d) 5-10% TS
View Answer
Answer: b
Explanation: 20-40% TS is a preferred substrate for biogas production. It is the solid waste in
the incoming municipal and residential waste and hence is also called as solid waste.
3. What are the categories for organic dry matter on the basis of total solids (TS)?
a) Low grade, medium grade, high grade and fixed bed
b) Low grade, medium grade, fluidized bed and fixed bed
c) Low grade, medium grade, high grade and solids
d) Downdraft, circulation fluidized bed, high grade and fixed bed
View Answer
Answer: c
Explanation: The categorization on the basis of TS are low grade with less than 1%, medium
grade with TS between 1and 5%, high grade with TS between 5 and 20% and finally solids
with TS between 20 and 40%. Fixed bed and fluidized bed are types of gasifiers.
4. Which among the following is the best source for methane production?
a) Metallic scrap
b) E-waste
c) Plastic waste
d) Water hyacinth
View Answer

Answer: d
Explanation: Water hyacinth is the best source for methane production in the given options.
It is an aquatic weed with huge biomass, high C/N ratio and lignin content. Thus, yielding
high amounts of methane.
5. Which of the following is used to produce biogas from biomass?
a) Anaerobic treatment
b) Aerobic treatment
c) Fermentation
d) Pyrolysis
View Answer
Answer: a
Explanation: Anaerobic treatment of municipal and residential waste is used to produce
biomass. Fermentation is used to produce ethanol and pyrolysis is used to produce gaseous
products like hydrogen.
6. Which of the following best indicates the steps of anaerobic digestion?
a) Waste water feed → biogas storage → generator → biogas
b) Waste water feed → digester → biogas → biogas storage → generator
c) Generator → waste water feed → digester → biogas → biogas storage
d) Waste water feed → biogas → digester → biogas storage → generator
View Answer
Answer: b
Explanation: Waste water feed is first sent into the anaerobic digester. The waste water is
treated to produce biogas which is then stored in a special storage. The fuel is then used to
produce electricity by driving a generator or for any other application.
7. Which of the following best indicates the steps inside an anaerobic digester?
a) Hydrolysis → methanogenesis → acetogenesis → acidogenesis
b) Hydrolysis → acidogenesis → methanogenesis → acetogenesis
c) Hydrolysis → acidogenesis → acetogenesis → methanogenesis
d) Methanogenesis → acidogenesis → acetogenesis → hydrolysis
View Answer
Answer: c
Explanation: The waste is first hydrolyzed and then acidized. After acidizing, the product is
then used to produce acetates which is further used to create methane in the final stage.
Methanogenesis is the process of creating methane.
8. What occurs in the hydrolysis step of anaerobic digestion?
a) Large polymers combine with water molecules
b) Large polymers break down to form water molecules
c) Small polymers combine to form large polymers with the help of water molecules
d) Large polymers break down into amino acids, fatty acids and simple sugars
View Answer
Answer: d
Explanation: Hydrolysis is used to break large polymers in the presence of an acid catalyst.
Large polymers present in the waste break down into amino acids, fatty acids and simple
sugars.

9. Acidogenesis further break down the molecules received from hydrolysis in anaerobic
digestion.
a) True
b) False
View Answer
Answer: a
Explanation: In acidogenesis, microorganisms further break down the molecules after
hydrolysis. This is because these molecules are still too large and cannot be used to generate
methane. The microorganisms produce an acidic environment for the break down to occur.
10. Which of the following is produced in acetogenesis?
a) Ethanol
b) Acetate
c) Acetone
d) Ketone
View Answer
Answer: b
Explanation: In acetogenesis, a derivative of acetic acid called acetate is produced from
carbon and other energy sources. This occurs in the presence of microorganisms called
acetogens.
11. Which of the following is produced apart from acetates in acetogenesis step in anaerobic
digestion?
a) Carbon monoxide
b) Charcoal
c) Carbon dioxide
d) Acetone
View Answer
Answer: c
Explanation: Apart from acetates, carbon dioxide and hydrogen are also produced in
acetogenesis. It is important to note that acetic acid is first produced which is then
converted into acetates.
12. What are the two ways to produce methane in methanogenesis step?
a) Converting carbon monoxide and carbon dioxide into methane
b) Converting carbon monoxide and acetic acid (or acetate) into methane
c) Converting methane into carbon monoxide and carbon dioxide
d) Converting carbon dioxide and acetic acid (or acetate) into methane
View Answer
Answer: d
Explanation: Methanogenesis is the process of producing methane by methanogens. In
anaerobic digestion, methanogenesis occurs by converting carbon dioxide and acetic acid (or
acetate) into methane.
13. Methanogens can directly use the products of hydrolysis to produce methane.
a) False
b) True
View Answer

Answer: a
Explanation: Methanogens cannot directly use the products of hydrolysis to produce
methane. The molecules are still too large and need to be broken down. This occurs in the
acidogenesis step.
14. What are the two main products of anaerobic digestion?
a) Carbon monoxide and hydrogen
b) Methane and carbon dioxide
c) Methane and carbon monoxide
d) Hydrogen and carbon dioxide
View Answer
Answer: b
Explanation: The purpose of anaerobic digestion is to convert the municipal waste (biomass)
into biogas. So, the two main products are methane and carbon dioxide. Carbon monoxide is
not the main product.
15. Gases emitted from the digester indicates the amount of biomass left to be broken down.
a) True
b) False
View Answer
Answer: a
Explanation: Gases emitted from the digester indicates the amount of biomass left to be
broken down. Production levels are a good indication of production abnormalities and hence
this technique is widely used in industries.

Module- 4
Hybrid System
HYBRID POWER SYSTEMS-
As convention fossil fuel energy sources diminish and the world’s environmental
concern about acid deposition and global warming increases, renewable energy sources
(solar, wind, tidal, biomass and geothermal etc) are attracting more attention as
alternative energy sources. These are all pollution free and one can say eco friendly.
These are available at free of cost. In India, there is severe power shortage and associated
power quality problems, the quality of the grid supply in some places is characterized by
large voltage and frequency fluctuations, scheduled and un scheduled power cuts and
load restrictions. Load shedding in many cities in India due to power shortage and faults
is a major problem for which there is no immediate remedy in the near future since the
gap between the power demand and supply is increasing every year. This led to rapid
usage of stand-by petrol or diesel generator sets and conventional battery inverter sets in
both urban and rural areas. Shopkeepers, house owners and offices commonly use 1-5
kW fuel generators in India when utility exercises load shedding.
*In India wind and solar energy sources are available all over the year at free of
cost whereas tidal and wave are costal area. Geothermal is available at specific location.
To meet the demand and for the sake of continuity of power supply, storing of energy is
necessary.
*Hybrid power system-The term hybrid power system is used to describe any power system
combine two or more energy conversion devices, or two or more fuels for the same device, that
when integrated, overcome limitations inherent in either.
*Usually one of the energy sources is a conventional one (which necessarily does
not depend on renewable energy resource) powered by a diesel engine, while the other(s)
would be renewable viz. solar photovoltaic, wind or hydro.
The design and structure of a hybrid energy system obviously take into account
the types of renewable energy sources available locally, and the consumption the system
supports. For example, the hybrid energy system presented here is a small-scale system
and the consumption of power takes place during nights, so the wind energy component
will make a more significant contribution in the hybrid system than solar energy.
Although the energy produced by wind during night can be used directly without storage,
a battery is needed to store solar and wind energy produced during the day.
In addition to the technical considerations, cost benefit is a factor that has to be
incorporated into the process of optimizing a hybrid energy system. In general, the use of
wind energy is cheaper than that of solar energy. In areas where there is a limited wind
source, a wind system has to be over-dimensioned in order to produce the required
power, and this results in higher plant costs.
It has been demonstrated that hybrid energy systems (renewable coupled with
conventional energy source) can significantly reduce the total life cycle cost of a
standalone power supplies in many off-grid situations, while at the same time providing a
reliable supply of electricity using a combination of energy sources. Numerous hybrid
systems have been installed across the world, and expanding renewable energy industry

has now developed reliable and cost competitive systems using a variety of technologies.
Research in the development of hybrid systems focused on the performance analysis of
demonstration systems and development of efficient power converters, such as bidirectional
inverters, battery management units (storage facilities), and optimization of different sources of
energy Sources, etc.
Hybrid power systems combine two or more energy conversion devices, or two or
more fuels for the same device, that when integrated, overcome limitations inherent in
either.
Hybrid systems can address limitations in terms of fuel flexibility, efficiency, reliability,
emissions and / or economics.
Classifications
According to Wichert (1997), hybrid energy systems with or without renewables, are
classified according to their configuration as series, switched hybrid, or parallel hybrid.
Series hybrid system
In this system either the renewable energy source or the diesel generator is used to
maintain charge in a large battery bank. During periods of low electricity demand the
diesel generator is switched off and the load can be supplied from PV together with
stored energy. Power from the battery bank is converted to AC at mains voltage and
frequency by a converter and is then fed to the load. Battery charging can be controlled
by controlling the excitation of the alternator (Wichert, 1997). The charge controller
prevents overcharging of the battery bank from PV generator when the PV power
exceeds the load demand and the batteries are fully charged. The system can be operated
in manual or automatic mode, with the addition of appropriate battery voltage sensing
and start/stop control of the engine-driven generator.
Advantages of this system include that the engine-driven generator can be sized to
be optimally loaded while supplying the load and charging the battery bank, until the
state of charge (SOC) of 70-80% is reached. No switching of AC power between the
different energy sources is required thus simplifying the electrical output interface. Also
the power supplied to the load is not interrupted when the diesel generator is started and
the inverter can generate a sine-wave, modified square-waves, or square-wave, depending
on the application.
Disadvantages are: low overall efficiency due to the series configuration of system elements;
substantially larger battery capacity than the maximum peak load demand resulting in the system
being more expensive component to the system; and with renewable inputs, there is limited

control of diesel alternator because the system is based on level of charge in the battery rather
than the site load.
A series hybrid system is characterized by low overall system efficiency since the diesel cannot
supply power directly to the load; large inverter and due to the cycling profile large battery bank
is required to limit the depth of discharge; and limited optimisation of diesel alternator and
renewable energy sources (SOPAC Miscellaneous Report 406, 2005). The battery bank is cycled
frequently, shortening its lifetime. If the inverter fails there is complete loss of power to the load,
unless the load can be supplied directly from the diesel generator for emergency purposes.
Switched hybrid system
This system allows with either the engine-driven generator or the inverter as the AC source but
no parallel operation of the main generation source is possible (Islam, 1999).Both the diesel
generator and the PV array can charge the battery bank. The diesel alternator meets the load
during the day and evening peak while the battery bank is charged by the renewables and any
excess power from the diesel. Power is supplied to the load by the battery through the inverter
during the low load night period. The typical layout of the system is as shown in figure .
Figure Switched configuration
Parallel hybrid System

The parallel configuration shown in figure allows all energy sources to supply the
load separately at low or medium demand, as well as supplying quick load from combined sources by
synchronizing the inverter with the alternator output wave form the bi-directional inverter can charge the
battery bank when access energy is available from the engine driven generator, as well as act as DC-AC
converter In this case the renewables and the diesel generator supply part of the load demand directly. The
diesel generator and the inverter run in parallel.
Figure : Parallel configuration
Advantages of this configuration over other system configurations are that the system load can be met in
the most optimal way, diesel efficiency can be maximized, diesel generator maintenance can be
minimized and there is a reduction in the capacities of diesel, battery and renewable sources while load
peaks are being met. However, automatic control is essential for the reliable operation of the system and
the system operation is less transparent to the untrained user of the system. Also the inverter has to
be a true sign wave inverter with the ability to synchronize with a secondary AC source.

Multiple Choice Questions and answers
1-Which of the following is (are) renewable resource(s)
(A) wind
(B) tides
(C) geothermal heat
(D) all of the above
2-Which of the following country generate all their electricity using renewable energy?
(A) Iceland
(B) England
(C) USA
(D) China
3-Renwable energy often displaces conventional fuel in which of the following area
(A) space heating
(B) transportation
(C) electricity generation
4-Which of the following is used as fuel for transportation
(A) ethanol
(B) aldehyde
(C) ketone
5-Biodiesel is produced from oils or fats using
(A) fermentation
(B) transesterification
(C) distillation
(D) none of the above
6-Photovoltaic cell converts solar energy into
(A) heat energy
(B) electric energy
(C) mechanical energy
(D) chemical energy
7-In which of the following region winds are stronger and constant
(A) deserts
(B) offshore
(C) low altitudes sites

8-Following country met more than 40% of its electricity demand from wind energy
(A) Denmark
(B) Portugal
(C) Ireland
(D) Spain
9-Concentrated solar power (CSP) systems use to focus a large area of sunlight into a small
beam.
(A) lenses
(B) mirrors
(C) tracking systems
10- The difference, in temperature between the core of the planet and its surface, is known as
(A) geothermal coefficient
(B) geothermal gradient
(C) geothermal constant
(D) none of the above
11- Biomass can be converted to
(A) methane gas
(B) ethanol
(C) biodiesel
12- The International Renewable Energy Agency (IRENA) was formed in
(A) 2008
(B) 2009
(C) 2010
(D) 2011
13-Which of the following was the first solar powered aircraft to complete a circumnavigation of the
world?
(A) Solar impulse
(B) Solar impulse 2
(C) Solar impulse 3
(D) Solar impulse 4
14- Following is true for biomass and biofuels
(A) their contribution in reduction in CO2 emissions is limited
(B) both emit large amount of air pollution when burned
(C) they consume large amounts of water
ANSWERS:
1-(D), 2-(A), 3-(D), 4-(A), 5-(B), 6-(B), 7-(B), 8-(A), 9-(D), 10-(B), 11-(D), 12-(B), 13-(B), 14-(D)

1. Which of the following is a nonrenewable energy resource?
solar
methane
hydroelectric
coal
2. The amount of oil that may become available for use is called oil .
reserves
reservoirs
resources
traps
3. A coal deposit that is not economical to mine today would be considered part of
our .
coal reserves
coal resources
coal reservoirs
none of these
4. What is the leading source of energy used in the United States today?
coal
oil resources
natural gas
nuclear power
5. The first oil well was drilled in the United States in .
1829
1859
1929
1959

A histogram showing percentages of various types of energy used in the United
States in 1997 is given above.
6. Area W represents
coal
solar
nuclear
oil
7. Area X represents
coal
solar
nuclear
oil
8. Area Y represents
coal
solar
nuclear
oil

9. Area Z represents
coal
solar
nuclear
oil
10.Oil, coal and natural gas supply approximately % of the energy used
in the United States
10
25
40
90
11.Of all of the energy produced in the United States, what % is lost in distribution
and inefficient use?
10
25
40
50
12.Chemical reactions triggered by transform organic material into
hydrocarbons.
solar energy
hydroelectric
elevated temperatures
decomposition
13.Energy resources derived from natural organic materials are called .
geothermal energy sources
fossil fuels

biomass
all of these
14.A permeable rock that contains hydrocarbon fluids and gasses is called a(n)
oil trap
source bed
oil reservoir
none of these
15.All oil traps contain .
an impermeable layer
an anticline
a fault
all of these
16.Which of the following is least likely to contain an oil trap?
an anticline
fault
natural stratigraphy
syncline
Cross section of an oil trap. X, Y, and Z represent three distinct fluid layers
within the permeable reservoir rock.
17.The oil trap shown here is a(n)

an anticline
fault trap
stratigraphic trap
salt dome trap
18.Layer X is most likely to be reservoir rock containing in the pore
space.
syncrude
water
natural gas
oil
19.Layer Y is most likely to be reservoir rock containing in the pore
space.
syncrude
water
natural gas
oil
20.Layer Z is most likely to be reservoir rock containing in the pore
space.
syncrude
water
natural gas
oil
21.Which of the following rock types would most likely be the best oil reservoir?.
granite
shale
sandstone
salt

22.In an oil trap formed by an anticline, accumlulates on top, in
the middle, and at the bottom.
natural gas .... oil..... groundwater
ground water .... oil..... natural gas
oil .... groundwater..... natural gas
oil .... natural gas......ground water
23.Two-thirds of the world's known oil reserves are located in .
Siberia
Gulf of Mexico and Caribbean
the middle East
Indonesia
24.The world has the least amount of which of the following fuel types..
oil
coal
uranium
there are roughly equal amounts of each of these fuels
25.At the current rate of world use, the remaining oil will be depleted in
approximately years.
25
100
400
2000
26.Which of the following statements is true?
in the US oil production is greater than oil consumption
in the US oil production equals oil consumption
in the US oil production is less than oil consumption

27.Most of the natural gas used in the United States is consumed by .
industry
residential use
electrical utilities
transportation
28.Burning of which of the following fuels produces the least amount of carbon
dioxide per unit of energy?
coal
oil
natural gas
all of these produce the same amount of carbon dioxide.
29.Layer X is .
anthracite
bituminous
lignite
tar
30.Layer Y is .
anthracite
bituminous

lignite
tar
31.Layer Z is .
anthracite
bituminous
lignite
tar
32.In addition to increasing temperature and pressure, the arrow to the left of the
diagram represents increasing
metamorphism
heat value
carbon content
all of the above
33.Which country contains about 50% of the world's coal resources?
United States
China
Canada
the former Soviet Union
34.In the United States, coal resources should last approximately years at
the current rate of use.
25
100
400
2000
35.Which of the following problems is associated with the burning of coal?

acid rain
carbon dioxide emissions
ash with toxic metal impurities
all of these
36.Oil derived from coal, oil shales or tar sands is called .
natural gas
biomass
syncrude
none of these
37.Nuclear energy is derived by .
combustion of atoms of U 235
fission of atoms of U 235
fusion of atoms of U 235
the breaking of U 235 bonds
38.Which of the following energy sources does not produce carbon dioxide?
oil
Uranium
coal
natural gas
39.About how many nuclear power plants are there in the US?
10
100
250
500
40.Which of the following statements regarding the nuclear accident at Chernobyl
in the Ukraine in 1986 is false?

radioactive debris was blown into Scandinavia and western Europe
hundreds of square miles of land surrounding Chernobyl was contaminated
and made uninhabitable
food supplies in many countries had to be purified in order to be consumed
excess deaths from cancer may be in the thousands over the next 40 years
41.Most of the uranium ore in the United States is located in the
Applachian Mountains
Basin and Range
Colorado Plateau
Great Lakes
42.The primary barrier to using solar energy in the United States is that
solar power is not technically feasible
solar power causes major pollution problems
solar power is not economically competitive with other energy sources
all of these
43.Hydroelectric energy provides about of the energy consumed annually
in the United States.
4%
12%
30%
65%
44.Solar energy stored in material such as wood, grain, sugar, and municipal waste
is called .
fossil fuels
biomass
geothermal energy
natural gas

45.What type of energy is derived from heated groundwater?
solar energy
geothermal energy
hydroelectric energy
nuclear energy
46.The largest geothermal power plant in the United States is located near which
city?
Chicago
Los Angeles
New York
San Francisco
47.The Geysers produce enough electricity to meet what portion of the needs of
San Francisco?
10%
25%
50%
75%
48.The world faces an energy crisis because .
world demand for energy will increase
world oil production will peak and begin to decline
shortages and the resulting escalation of prices can shock the economic and
political order
all of the above
Multiple Choice Questions and Answers
1. What does Heating and cooling of the atmosphere generates?
a)Thermo line circulation
b) Radiation currents

c) Convection currents
d) Conduction currents
Answer: c
Explanation: Wind energy can be economically used for the generation of electrical energy.
Heating and cooling of the atmosphere generates convection currents. Heating is caused by
the absorption of solar energy on the earth surface.
2. How much is the energy available in the winds over the earth surface is estimated to be?
a) 2.9 X 120 MW
b) 1.6 X 107 MW
c) 1 MW
d) 5MW
Answer: b
Explanation: The energy available in the winds over the earth surface is estimated to be 1.6 X
107 MW which is almost the same as the present day energy consumption. Wind energy can
be utilized to run wind mill which in turn, is used to drive the generators.
3. How much wind power does India hold?
a) 20,000 MW
b) 12,000 MW
c) 140,000 MW
d) 5000 MW
Answer: a
Explanation: India has a potential of 20,000 MW of wind power. Wind power accounts
nearly 9.87% of India’s total installed power generation capacity. Generation of wind power
in India mainly account from southern state of India.
4. What is the main source for the formation of wind?
a) Uneven land
b) Sun
c) Vegetation
d) Seasons
Answer: b
Explanation: Wind is free and renewable form of energy, which throughout history has been
used to grind grain, power ships, and pump water. Wind is created when the sun unevenly
heat the earth surface.
5. Which country created wind mills?
a) Egypt
b) Mongolia
c) Iran
d) Japan
Answer: c
Explanation: The earliest known wind mills were in Persia (Iran). These early wind mills
looked like large paddle wheels. Centuries later, the people of Holland improved the basic
design of wind mill. Holland is famous for its wind mills.
6. “During the day, the air above the land heats up more quickly than the air over water”.
a) True
b) False
Answer: a
Explanation: During the day, the air above the land heats up more quickly than the air over water.
The warm air over the land expands and raises, and the heavier, cooler air rushes in to take its
place, creating winds.

7. What happens when the land near the earth’s equator is heated?
a) All the oceans gets heated up
b) Small wind currents are formed
c) Rise in tides
d) Large atmospheric winds are created
Answer: d
Explanation: The large atmospheric winds that circle the earth are created because the land
near the earth’s equator is heated more by the sun than the land near the north and south
poles. Wind energy is mainly used to generate electricity.
8. What type of energy is wind energy?
a) Renewable energy
b) Non-renewable energy
c) Conventional energy
d) Commercial energy
Answer: a
Explanation: Wind is called a renewable energy source because the wind will blow as long as
the shines. Wind power, as an alternative to burning fossil fuels, is plentiful, renewable,
widely distributed, clean, produces no greenhouse gas emissions during operation, consumes
no water, and uses little land.
9. What are used to turn wind energy into electrical energy?
a) Turbine
b) Generators
c) Yaw motor
d) Blades
Answer: a
Explanation: Wind turbine blades capture wind energy, a form of mechanical energy, and put it
to work turning a drive shaft, gearbox, and generator to produce electrical energy. Many factors
affects wind turbine efficiency including turbine blade aerodynamics.
10. What is the diameter of wind turbine blades?
a) 320 feet
b) 220 feet
c) 80 feet
d) 500 feet
Answer: b
Explanation: Large utility-scale wind turbines can now generate more than a MW of
electrical power each and deliver electricity directly in to the electric grid, these turbines are
placed at 200 feet height at the rotor hub and have blades which are 220 feet or more in
diameter.
11. At what range of speed is the electricity from the wind turbine is generated?
a) 100 – 125 mph
b) 450 – 650 mph
c) 250 – 450 mph
d) 30-35 mph
Answer: d
Explanation: Wind turbines are designed with cut-in wind speeds and cut-out speeds i.e. the
wind speeds when the turbines start turning or shut off to prevent drive train damage.
Typically, maximum electric generations occurs at speeds of 30-35mph.

12. When did the development of wind power in India began?
a) 1965
b) 1954
c) 1990
d) 1985
Answer: c
Explanation: The development of wind power in India began in 1990s. Presently India is the
world’s fourth largest wind power generator. The Indian energy sector has an installed
capacity of 32.72 GW. Today India is a major player in the global wind energy market.
“Components of Wind Energy Conversion System”.
1. How much power does the small scale wind machine generate?
a) 18 KW
b) 2 KW
c) 12 KW
d) 30 KW
View Answer
Answer: b
Explanation: These might be used on farms remote applications and other places requiring
relatively low power. The generating capacity is up to 2kW. Small scale wind machines lower
your electricity bills by 50% – 90%.
2. Which type of wind machines are used at several residence or local use?
a) Large size machines
b) Remote machines
c) Small size machines
d) Medium size machines
View Answer
Answer: d
Explanation: These wind turbines may be used to supply less than 100 kW rated capacity, to
several residences or local use. These do not require much space they can be installed on roof tops
or on some high elevated areas.
3. Which type of wind turbines produce 100 kW or greater?
a) Large machines
b) Small machines
c) Medium machines
d) Remote Machines
View Answer
Answer: a
Explanation: Large wind turbines are those of 100 kW rated capacity or greater. They are used to
generate power for distribution in central power grids. They can have single generator at a single
site or multiple generators sited at several places over an area.
4. Which part of the wind mill acts as a housing for the turbine?
a) Wind Vane
b) Shaft
c) Wind mill head
d) Turbine
View Answer

Answer: c
Explanation: The wind mill head supports the rotor, housing, and rotor bearings. It also has control
mechanism like changing the pitch of the blades for safety devices, tail vane to orient the rotor to
face the wind. Its body is the size of the mini bus.
5. A rotor installed in a fixed orientation with the swept area perpendicular to the pre dominate wind
direction is called
a) Nacelle
b) Yaw fixed machines
c) Blades
d) Anemometer
View Answer
Answer: b
Explanation: In the locations with the prevailing wind in one direction, the design of a turbine can
be greatly simplified. The rotor can be installed in a fixed orientation with the swept area
perpendicular to the pre dominate wind direction. This machine is called yaw fixed.
6. How is the action of yaw controlled in small turbines?
a) Tail vane
b) Blades
c) Shaft
d) Yaw motor
View Answer
Answer: a
Explanation: In small turbines, yaw action is controlled by a tail vane while is larger machines a
servomechanism operated by a wind-direction sensor controls the yaw motor keeping the turbine
properly oriented.
7. Which part of the wind turbines senses wind speed, wind direction, shaft speed and torque?
a) Turbine blade
b) Shaft
c) Rotor
d) Controller
View Answer
Answer: d
Explanation: The controller senses wind speed, wind direction, shafts speeds and torques, output
power and generator temperature, Control signals are generated with the electrical output
corresponding to the wind energy input.
8. Which type of wind turbine has low RPM?
a) Small wind turbine
b) Large wind turbine
c) Medium wind turbine
d) Remote wind turbine
View Answer
Answer: b
Explanation: The rate of rotation of large wind turbine generators operating at rated capacity or
below is controlled by varying the pitch of the rotor blades. It has low rpm, about 40 to 50. It is
necessary to increase greatly the low rotor rate of turning using transmission mechanism.
9. Why recommendation of fixed ratio gears done for top mounted equipment?
a) Because they are easy install
b) Requires less space
c) Due to its low cost

d) Because of their high efficiency
View Answer
Answer: d
Explanation: Fixed ratio gears are recommended for top mounted equipment because of their high
efficiency, and minimum system risk. For bottom mounted equipment requiring a right angle drive
transmission costs can be reduced on the hub by increasing rotor speed to generator.
10. Which type of generator are made use in wind turbines?
a) Recreational generators
b) Synchronous generator
c) Asynchronous generator
d) Alternator
View Answer
Answer: b
Explanation: Generators may be either constant or variable speed type. Variable speed units are
expensive and/or unproved. Constant speed generator in use are synchronous induction and
permanent magnet types. Synchronous unit is used for large aero generator systems. It is very
versatile and has an extensive data base.
11. In which part do we find sensors and actuators?
a) Fixed gears
b) Turbines
c) Control systems
d) Blades
View Answer
Answer: c
Explanation: Control systems involves sensors and actuators. The modern large wind turbine
generator requires a versatile and reliable control system. A control system is used for i) changing
the orientation of the rotor into the wind. ii) Start up and cut-in of the equipment. iii) Power
control of the rotor by varying the pitch of the blades.
12. How many types of supporting tower for wind mill are generally used?
a) 2
b) 4
c) 3
d) 5
View Answer
Answer: b
Explanation: Four types of generating tower are used generally:
i) The reinforced concrete tower
ii) The pole tower
iii) The built up shell tube tower
iv) The truss tower.
13. On what does the selection of supporting structure depends?
a) Length of blades
b) Rotating capacity
c) Capacity of generator
d) Transmission systems
View Answer
Answer: d
Explanation: The type of the supporting structure and its height is related to cost and the

i
i
i
transmission system incorporated. Horizontal axis wind turbines are mounted on towers so as to be
above the level of turbulence and other ground related effects.
14. At what type of location vibrations are more in the wind turbine?
a) Downwind location
b) Up wind location
c) Windward
d) Leeward
View Answer
Answer: b
Explanation: In the upwind location (i.e. the wind encounters the turbine before reaching the
tower), the wake of the passing rotor blades causes repeated changes in the wind forces on the
wind forces on the tower. Due to this the tower may vibrate and may eventually be damaged.
15. At what type of location vibrations are less in the wind turbines?
a) Windward
b) Leeward
c) Downwind location
d) Upwind Location
View Answer
Answer: c
Explanation: If the turbine is downwind from the tower, vibrations are less but the blades are
subjected to severe alternating forces as they pass through the tower wake. Downwind rotors are
generally preferred for large aero generators.
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Velocity
and Power from Wind”.
1. Select the formula for total power pt?
a) Pt = 1/2gc ρAV3
b) Pt = ρAV3
D3
c) Pt = 12gc V3
D3
d) Pt = 2gcVi3
View Answer
Answer: a
Explanation:
2. Why blade velocity of wind turbine varies?
a) Due to varying wind speeds
b) Long length of blades
c) Due to the height of mount

d) Because of hotness of Sun
View Answer
Answer: b
Explanation: Wind turbine experiences change in velocity dependent upon the blade inlet angle
and the blade velocity. Since the blades are long, the blade velocity varies with the radius to a
greater degree than steam or gas-turbine blades and the blades are therefore twisted.
3. When was the Hall a day wind mill introduced?
a) 1920
b) 1923
c) 1854
d) 1864
View Answer
Answer: c
Explanation: Invented by Daniel Halladay in 1854, the Halladay Standard was the first
commercially successful self-governing windmill in 1854 was the firms of Halladay, McCray &
Co., Ellington, Conn. Partners in the company were inventor Daniel Halladay, John Burnham and
Henry McCray.
4. How much ideal efficiency should practical turbine have?
a) 10 – 12%
b) 18 – 25%
c) 80 – 90%
d) 50 – 70%
View Answer
Answer: d
Explanation: As wind turbine wheel cannot be completely closed, and because of spillage and
other effects, practical turbines have 50 to 70% of the ideal efficiency. The real efficiency η is the
product of this and ηmax and is the ratio of an actual to total power.
P = ηPtot.
5. How many types are acting on propeller type wind mill?
a) 2
b) 3
c) 4
d) 5
View Answer
Answer: a
Explanation: There are two types of forces operating on the blades of a propeller type wind
turbine. They are the circumferential forces in the direction of wheel rotation that provide the
torque and the axial forces in the direction of the wind stream that provide an axial thrust that must
be counteracted by proper mechanical design.
6. Calculate the air density, when 10m/s wind is at 1std atmospheric pressure and 15o
C?
a) 1.226 kg/m3
b) 1.033 kg/m3
c) 2.108 kg/m3
d) 0.922 kg/m3
View Answer
Answer: a
Pa
Air density, ρ = P/RT = (1.01325 ×105
)/(287(15+273.15)) = 1.226 kg/m3
.

7. Calculate the air density when 18m/s wind is at 1std atmospheric pressure and 34o
C?
a) 1.149 kg/m3
b) 1.9 kg/m3
c) 2.88 kg/m3
d) 5.89 kg/m3
View Answer
Answer: a
Pa
Air density, ρ = P/RT = (1.01325 × 105
)/(287(34+273.15)) = 1.149 kg/m3
.
a) 0.277 KW
b) 1.224 KW
c) 4.28 KW
d) 0.89 KW
View Answer
Answer: a
P = 0.245 X (πD2
/4)
= 0.245 X (π (120)2
/4)
= 0.277 KW.
a) 0.155KW
b) 0.982 KW
c) 1.452 KW
d) 3.12 KW
View Answer
Answer: a
P = 0.245 X (πD2
/4)
= 0.245 X (π (90)2
/4)
= 0.155KW.
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Wind
Turbine Operation”.
View Answer
Answer: c

Answer: c
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: d
(MCQs) focuses on “Horizontal Axis Wind Mill”.
View Answer
Answer: a
a) True
b) False
View Answer
Answer: a
their fatigue life.
View Answer
Answer: b
directions.

a) 4
b) 2
c) 7
d) 6
View Answer
Answer: d
a) 1
b) 2
c) 3
d) 4
View Answer
Answer: c
View Answer
Answer: b
View Answer
Answer: a
(MCQs) focuses on “Wind Turbine Operation”.

View Answer
Answer: c
View Answer
Answer: a
b) Tenancy
c) Flat Rating
d) TRP
View Answer
Answer: c
a) Cut in velocity
b) Windward
c) Cut out velocity
d) Upwind location
View Answer
Answer: a
View Answer
Answer: a

b) Flat rating
c) Cut in velocity
d) Cut out velocity
View Answer
Answer: a
c) flat rating
d) cut out velocity
View Answer
Answer: a
a) 2
b) 3
c) 4
d) 5
View Answer
Answer: a
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: a
tower.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer

Answer: b
appearance.
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: c
a) Post mill
b) Smock mill
c) Tower mill
d) Fan mill
View Answer
Answer: d
This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on
“Horizontal Axis Wind Mill”.
View Answer
Answer: a
a) True
b) False
View Answer
Answer: a
their fatigue life.

View Answer
Answer: b
directions.
View Answer
Answer: d
View Answer
Answer: c
View Answer
Answer: d
View Answer
Answer: d

a) Tip speed ratio
View Answer
Answer: a
a) 4
b) 2
c) 7
d) 6
View Answer
Answer: d
a) 1
b) 2
c) 3
d) 4
View Answer
Answer: c
View Answer
Answer: b
View Answer
Answer: a

This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Vertical
Axis Wind Mill”.
1. In which wind measuring device a tubular piece of thin flexible fabric hanged vertically to
determine direction?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: a
Explanation: Wind sock is a very basic device that measure wind direction and provide a rough
idea of the wind’s intensity. A wind sock is a tubular piece of fabric or thin, flexible fabric
attached to a pole. When there is no wind, the fabric hangs vertically from the attached pole.
2. A device which is used as device for showing direction wind as well used as a decorative purpose?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: b
Explanation: A weather vane works similarly to wind sock. Instead of a tubular sock, the weather
vane is made by placing a horizontal pole at the top of vertical pole. The poles are joined together
so that the horizontal pole has a flattened, vertical end that reacts to wind.
3. Which is the wind direction showing device that spins perpendicularly?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: c
Explanation: A pinwheel is a windmill-style turbine that spins perpendicularly to the wind
affecting it. Like wind socks and weather vanes, a pinwheel can be attached to a rotating base.
This allows the pinwheel to change direction with the wind, and it will spin facing into the
oncoming wind.
4. Which is the device that measures wind direction and its intensity?
a) Wind socks
b) Weather vane
c) Pin wheels
d) Anemometers
View Answer
Answer: d
Explanation: An anemometer is any device that measures wind direction and intensity. It may be
simple, such as the devices described above, or it may be a complex, computer-aided machine that
measures and records wind patterns over time. More advanced anemometer machines are used to
aid in professional weather reporting and air traffic control.

5. What units does the anemometer measure in?
a) Feet per minute
b) Liters per minute
c) Centimeters per minute
d) Meter per seconds
View Answer
Answer: a
Explanation: The anemometer measures in feet per minute, or FPM. The rotation is sensed by a
magnetic or optical sensor that converts the signal to FPM measurement. An arrow on the vane
head identifies the direction the airflow must travel through the vane to obtain proper
measurements.
6. Which of the following type of turbine or the rotor requires relatively low velocity winds for
operation?
a) Cup anemometer
b) Savonius rotor
View Answer
Answer: b
Explanation: Savonius rotor is a simple WEC system which woks like a cup anemometer. This
type was invented by S.J. Savonius in the year 1920. It requires relatively low velocity winds for
operation. It consists of two half cylinders facing opposite directions forming as S-shaped cross
section.
7. Which type of axis does a Savonius Rotor has?
a) Horizontal axis
b) Mediolateral axis
c) Vertical axis
d) Lateral Axis
View Answer
Answer: c
Explanation: A Savonius wind energy conversion system has a vertical axis and hence eliminates
the expensive power transmission system from the rotor to the axis. Since it is a vertical axis
machine it does not matter much about the wind direction.
8. Why is Savonius rotor not suitable for installation?
a) Because of long drive shaft
b) Because of its low capacity motor
c) Because of its typical blade design
d) Due to the light material it is made of
View Answer
Answer: a
Explanation: Savonius rotor is not useful for very high installation because of long drive shaft
problems. Bracing of the topmost bearing above the rotor of a very tall vertical axis machine is
difficult requiring very long guy wires.
9. When was the Darrieus type machine invented?
a) 1925
b) 1932
c) 1929
d) 1948
View Answer

Answer: a
Explanation: Darrieus type machine was invented originally and patented in 1925 by G.J.M >
Darrieus, a French engineer. The Darrieus wind mill is a vertical axis machine that has the same
advantage of a modern rapidly rotating propeller type windmill, by use of an efficient airfoil,
effectively intercepts large area of wind with a small blade area.
10. What form of force acts on the blades of Darrieus machine?
a) Pure tension
b) Compression
c) Shear force
d) Air resistance force
View Answer
Answer: a
Explanation: Darrieus wind mill has two or three thin, curved blades with airfoil cross section and
constant chord length. Both ends of blades are attached to a vertical shaft. Thus the force in the
blade due to rotation is pure tension.
11. Which type of vertical wind machine has relatively low solidity and low starting torques?
a) Cup anemometer
b) Savonius rotor
View Answer
Answer: c
Explanation: Darrieus type rotors are lift devices characterized by curved blades with air foil cross
sections. They have relatively low solidity and low starting torques, but high tip to wind speeds
and therefore relatively high power outputs per given rotor weight and cost.
12. Which type of vertical wind machine consists of spinning cylinders?
a) Cup anemometer
b) Savonius rotor
View Answer
Answer: d
Explanation: Magnus effect rotor concept was first demonstrated by Magnus in 1912. It consists of
spinning cylinders. When cylinders spun in wind stream, translational forces are produced
perpendicular to the wind stream by the Magnus effect. Such a device can be used to propel ships
or land vehicles.
13. Aero turbine is the fraction of power in the wind through the swept area which is converted into
useful mechanical shaft power is called
a) Coefficient of performance
b) Coefficient of variation
c) Coefficient of lift
d) Coefficient of spin
View Answer
Answer: a
Explanation: The coefficient of performance of an aero turbine is the fraction of power in the wind
through the swept area which is converted into useful mechanical shaft power. Cp for horizontal
axis wind machine has theoretical maximum value = 0.593.

1-The amount of energy available in the wind at any instant is proportional to of the wind
speed.
(A) Square root power of two
(B) Square root power of three
(C) Square power
(D) Cube power
2-Wind energy is harnessed as energy with the help of windmill or turbine.
(A) Mechanical
(B) Solar
(C) Electrical
(D) Heat
3-Winds having following speed are suitable to operate wind turbines.
(A) 5 – 25m/s
(B) 10 – 35m/s
(C) 20 – 45m/s
(D) 30 – 55m/s
4-The following is (are) the classification of winds
(A) Global wind
(B) Local wind
(C) Both (A) and (B)
5-Global Cold wind move from
(A) Polar to equatorial region
(B) Equatorial to polar region
(C) Equatorial to oceanic region
(D) Oceanic to Equatorial region
6-Global Cold wind generated from Oceans moves to
(A) Mountains
(B) Equator
(C) Plain areas

(D) Poles
7- force is responsible for forcing the global winds towards westernly direction.
(A) Coriolis
(B) Gravitational
(C) Centripetal
(D) Centrifugal
8-Global winds towards westernly direction are known as
(A) Trade winds
(B) Western winds
(C) Eastern winds
9-Uneven heating occurs on land surface and water bodies are due to
(A) Air Currents
(B) Solar radiation
(C) Lunar eclipse
10- The following factor(s) affects the distribution of wind energy
(A) Mountain chains
(B) The hills, trees and buildings
(C) Frictional effect of the surface
11- The wind intensity can be described by
(A) Reynolds number
(B) Mach number
(C) Beaufort number
(D) Froude number
ANSWERS:
1-(D), 2-(A), 3-(A), 4-(C), 5-(A), 6-(C), 7-(A), 8-(A), 9-(B), 10-(D), 11-(C)
12- The wind speed is measured using an instrument called
(A) Pyranometer

(B) Manometer
(C) Anemometer
(D) Wind vane
13- The rate of change of wind speed with height is called
(A) Wind shear
(B) Wind rose
(C) Wind solidity
14- At gradient height the shear force is
(A) Zero
(B) Minimum
(C) Maximum
15-The gradient height is about m from the ground.
(A) 500
(B) 1000
(C) 1500
(D) 2000
16-The atmosphere with uniform wind speed is called the atmosphere
(A) Plain
(B) Surface
(C) Free
(D) Shear
17- Surface layer is the air layer considered from the height of local obstruction to a
height of about
(A) 50m
(B) 100m
(C) 150m

(D) 200m
18- Air layer from 100m that extends up to the gradient height is known as
(A) Surface layer
(B) Ekman layer
(C) Boundary layer
19- Low solidity rotors use which of the following force for rotation
(A) Drag
(B) Lift
(C) Centrifugal
(D) Centripetal
20- The following is the tangential velocity of the blade due to the rotation of blade.
(A) Wind velocity
(B) Incident wind velocity
(C) Blade linear velocity
(D) Relative velocity
21- Turbines blades have type cross section to extract energy from wind.
(A) Aerofoil
(B) Elliptical
(C) Rectangular
22- The Nacelle of windmill houses
(A) Gearbox
(B) Brakes
(C) Generator
ANSWERS:
12-(C), 13-(A), 14-(A), 15-(D), 16-(C), 17-(B), 18-(B), 19-(B), 20-(C), 21-(A), 22-(D)

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