Unit4 introduction to various renewable energy sources 0916

UNIT 4
POWER PLANT ENGG.
RENEWABLE ENERGY
Introduction to Various
Renewable Energy Sources
S.PALANIVEL ASSOCIATE PROF./MECH. ENGG
KAMARAJ COLLEGE OF ENGG. & TECH VIRUDHUNAGAR (NEAR)

TYPES OF RENEWALE SOURCES
Renewable Sources
Hydro Energy
Wind Energy
Solar Energy
Biomass Energy
Tidal Energy
Geothermal Energy
Wave Energy
Bio-fuel
Bagasse

Wind Energy

Wind Energy- Technology
• Differential heating of the earth’s surface
and atmosphere induces vertical and
horizontal air currents that are affected by
the earth’s rotation and contours of the land
and generates WIND.
• A wind turbine obtains its power input by
converting the force of wind into a torque
acting on the rotor blades.
• The amount of energy which the wind
transfers to the rotor depends on the
density of the air, the rotor area, and the
wind speed.
• PLF(Plant Load Factor) of wind farm is
normally in the range of 20% to 30%
depending upon the site conditions.

Wind Energy- Technology
• Major components of wind turbine

Internal Parts: The “Hub”

• Rotor- The hub and the blades
together are referred to as the
rotor. Wind turns the blades
which turn the drive shaft.
• Shaft- Two different shafts turn
the generator. One is used for
low speeds while another is used
in high speeds.
• Gear Box- Gears connect the
high and low speed shafts and
increase the rotational speeds
from about 10-60 rotations per
minute to about 1200-1800 rpm,
the rotational speed required by
most generators to produce
power.

• 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.
• Controller- Turns the blades on at 8-16 mph and shuts
them down around 65 to prevent any high wind
damage.
• Tower- Tall tubular metal shaft. The taller the tower,
the more power produced.

Turbines: Two Types
• Horizontal Axis Wind Turbines
• Vertical Axis Wind Turbines

Two Types
• Vertical Axis Advantages
• Can place generator on
ground
• You don’t need a yaw
mechanism for wind
angle
• Disadvantages
• Lower wind speeds at
ground level
• Less efficiency
• Requires a “push”
• Horizontal Advantages
• Higher wind speeds
• Great efficiency
• Disadvantages
• Angle of turbine is
relevant
• Difficult access to
generator for repairs

Energy: Kinetic to Electric
• Wind has kinetic energy: Energy of motion
• KE = ½ M * U2
• The Mass (M) of Air per second is
• volume (V) multiplied by its density (D)
• M = VD
• density of air = 1.2929 kilograms/m3
• The mass of air per second (M)
• traveling though a hoop is the area of the hoop (A)
• multiplied by speed of the wind per second (u)
• multiplied the density of air (D)
• M = AuD
• area of the hoop (A) is radius (r) squared
• A = П r2

• Turbines catch the wind's energy with their propeller-like
blades
• Usually, two or three blades are mounted on a shaft to form
a rotor
• The wind turbine blade acts an airplane wing
• When the wind blows a pocket of low-pressure air forms on
the downwind side of the blade
• Air pressure = force exerted on an object by the weight of
particles in air
• measured in:
• Inches of Mercury (“Hg),A
• Amospheres (Atm)
• Millibars (mb)
• 1013.25 mb = 29.92 “Hg = 1.0 atm.[2] At standard or normal
atmospheric pressure, and at 15° C, air usually weighs about
1.225 kilograms per cubic meter
[

• When air pressure is low in one locality, such as the
downwind side of a wind turbine blade, air from another area
will rush in to equal out the air pressure
• The low-pressure air pocket created by the wind turbine blade
then pulls the blade toward it, causing the rotor to turn
• This process is referred to as lift. The force of the lift is
actually much stronger than the wind's force against the front
side of the blade, which is called drag
• The combination of lift and drag causes the rotor to spin like a
propeller
• causes the spinning of the turbine’s shaft.
• When shaft spins KE of movement is converted by
generator into usable electricity

KE to Usable Energy

Bernoulli’s Principle
• Bernoulli’s Principle
• EnergyKinetic
+ EnergyPressure
= EnergyPressure
+ EnergyKinetic
• Example:
• If Energy Kinetic1
= (5), and Energy Pressure1
= (11)
• and Energy Pressure2
drops to (1)
• then Kinetic Energy2
Increases to (15)

Setup Types
•stand-alone
not connected to a power grid
power created is directly channeled into
powered site
•utility power grid
Stores energy
connection must be available
• Combined w/ a photovoltaic (solar cell) system
has solar cells mounted on it.
Solar cells - thin wafers of silicon which, when
exposed to sunlight, produce…electric current

Wind Plant
• large number of wind turbines are usually built
close together to form what is referred to as a
wind plant
• The world’s largest wind plant located off the
coast of Oregon has 450 wind turbines
• generates 300 MWh of energy
• meets the needs of 70,000 homes
• This practice utilizes an area suited for wind
energy by deploying multiple units

Limitations
• limit to the amount of energy that can be harnessed by an
individual wind turbine
• The more kinetic energy that a wind turbine pulls out of the
wind, the more the wind will be slowed down as it leaves
• If a designer tried to extract all the energy from the wind
• air would move away with the speed zero
• air prevented from entering the rotor of the turbine
• If the designer did the exact opposite and allowed the wind
to pass through the wind turbine without being hindered at
all, again,
• energy will not be cultivated,
• since the rotor blades would not be spun, the
• shaft wouldn’t spin
• kinetic energy would not be converted into electricityS.PALANIVEL ASSOCIATE PROF./MECH. ENGG

Betz Law
• designer of a wind turbine must find an ideal
balance between these two extremes
• Fortunately for wind energy advocates and
enthusiasts there is a simple answer to this
dilemma
• Under Betz Law an ideal wind turbine would slow
down the wind by 2/3 of its original speed (the
capture of 59.6% of the wind’s speed).

Site Limitations
• The direction that wind travels in
• angle of the turbine’s rotors are
• important limitations and considerations
• Wind at a site is being slowed down by each
turbine
• limit to the amount of individual units a site
can support
• NIMBY (somebody who objects to something
unattractive or potentially dangerous being
located near his or her home)
• Birds

Wind Energy
• Wind power technology is dominated by onshore
installations (land based) of turbines.
• Wind power is used for both captive consumption
and Independent Power Producer (IPP) model.

Wind Energy- Present
Scenario
• Wind Power- Fastest growing renewable energy
source.
• Globally, it grew at the average rate of 27% p.a.
over the past 10 years.
• While in India, it grew at the average rate of 33%
p.a. over the past 9 years.
• Presently, India is ranked 5th
in the world in terms
of Wind Energy installed capacity.

Wind Energy- Drivers &
Challenges

Solar Energy

What is a solar cell?
• Solid state device that converts solar energy
directly into electrical energy
• Efficiencies from 10%- 80%%
• No moving parts
• No noise
• Lifetimes of 20-30 years or more

Cross Section of Solar Cell

How Does Solar Cell Work?
• The junction of dissimilar materials (n (+) and p (-)
type silicon) creates a voltage,
• Energy from sunlight knocks out electrons,
creating a electron,
• Connecting both sides to an external circuit
causes current to flow,
• In essence, sunlight on a solar cell creates a small
battery with voltages typically 0.5 volt DC,

Combining Solar Cells
• Solar cells can be electrically connected in series
(voltages add) or in parallel (currents add) to give
any desired voltage and current,
• Power (Watts) output is calculated P = I x V
• Photovoltaic cells are typically sold in modules (or
panels) of 12 volts with power outputs of 50 to
100+ watts.
• These are then combined into arrays to give the
total desired power or watts.

Cells, Modules, Arrays

Photovoltaic Array for Lighting

The PV Market
• As prices dropped, PV began to be used for stand-
alone home power.
• If you didn’t have an existing electrical line close to
your property, it was cheaper to have a PV system
(including batteries and a backup generator) than
to connect to the grid.
• As technology advanced, grid-connected PV with
net metering became possible.

Other System Components
While a major component and cost of a PV system is
the array, several other components are typically
needed. These include:
• The inverter – DC to AC electricity
• DC and AC safety switches
• Batteries (optional depending on design)
• Monitor – (optional but a good idea)
• Ordinary electrical meters work as net meters

PV On Homes
• PV can be added to existing roofs.
• While south tilted exposure is best, flat roofs do
very well.
• Even east or west facing roofs that do not have
steep slopes can work fairly well if you are doing
net metering since the summer sun is so much
higher and more intense than the winter sun.
• The exact performance of any PV system in any
orientation is easily predictable.

Photovoltaic Array on Roof
and as an Overhang

Other Mounting Systems?
• If it is impossible or you don’t want to put a PV
system on your existing roof, it is possible to pole
mount the arrays somewhere near the house as
long as the solar exposure is good.
• Pole mounted solar arrays also have the potential
to rotate to follow the sun over the day by
installing a sun tracking system,
• Sun tracking systems can provides a 30% or more
boost to the PV system performance.

Pole Mounted PV

Roof Integrated PV
• If you are doing new construction or a reroofing
job, it is possible to make the roof itself a solar PV
collector.
• This saves the cost of the roof itself, and offers a
more aesthetic design.
• The new roof can be shingled or look like metal
roofing. A few examples follow.

Solar Energy- Technology
• Solar power is by far the Earth’s most available energy source, easily
capable of providing many times the total current energy demand.
• Solar power is the conversion of sunlight into electricity.
• Two main commercial ways of conversion of sunlight into electricity:
• Concentrating Solar Thermal Plant (CSP)
• Photovoltaic plants (PV)
• CSP and PV both have their markets, PV is very successful in decentralized
applications, where as CSP offers advantages for central and large-scale
applications.
• CSP power plants are the most cost-efficient way to generate and to store
dispatch able CO-free electricity. However, there is no competition
between both. Rather, they have to be seen as complementary
technologies.
• CUF of CSP- in the range of 20% to 30%
• CUF of PV- in the range of 15% to 20%

PV technology basics
Solar cells are semiconductor devices
that produce electricity from sunlight via the photovoltaic effect.
Sunlight strikes the cell, photons with energy above the
semiconductor bandgap impart enough energy to create
electron-hole pairs.
A junction between dissimilarly doped semiconductor layers sets
up a potential barrier in the cell, which separates the light-
generated charge carriers.
This separation induces a fixed electric current and voltage in the
device. The electricity is collected and transported by metallic
contacts on the top and bottom surfaces of
the cell.
Diagram of photovoltaic cell.
A typical silicon PV cell is composed of a
thin wafer consisting of an ultra-thin layer of
phosphorus-doped (N-type) silicon on top of
a thicker layer of boron-doped (P-type)
silicon.
An electrical field is created near the top
surface of the cell where these two materials
are in contact, called the
P-N junction.
When sunlight strikes the surface of a PV cell,
this electrical field provides momentum and
direction to light-stimulated electrons, resulting
in a flow of current when the solar cell is
connected to an electrical load
How PV Cells Work

PV systems are like any other electrical power generating systems, just the equipment used is different than that used
for conventional electromechanical generating systems.
Depending on the functional and operational requirements of the system,
the specific components required, and may include major components
DC-AC power inverter,
battery bank,
system and battery controller,
auxiliary energy sources
and sometimes the specified electrical load (appliances).
In addition, an assortment of balance of system (BOS) hardware,
Including wiring, overcurrent, surge protection and disconnect
devices, and other power processing equipment.
How a PV System Works

Batteries are often used in PV systems for the purpose of storing energy
produced by the PV array during the day, and to supply it to electrical loads
as needed (during the night and periods of cloudy weather).
Other reasons batteries are used in PV systems are to operate the PV array
near its maximum power point, to power electrical loads at stable voltages,
and to supply surge currents to electrical loads and inverters.
In most cases, a battery charge controller is used in these systems to
protect the battery from overcharge and overdischarge.
In many stand-alone PV
systems, batteries are used
for energy storage. Figure
shows a diagram of a typical
stand-alone PV system
powering DC and AC loads
Diagram of stand-alone PV system
with battery storage powering DC and AC loads.
Why Are Batteries Used in Some PV Systems?

How Are Photovoltaic Systems Classified?
Photovoltaic power systems are generally
classified according to:
• functional and operational
requirements,
• component configurations,
• how the equipment is
connected to other power
sources and electrical
loads.
The two principle classifications are
grid-connected or utility-
interactive systems
stand-alone systems.
Photovoltaic systems can be designed to
provide DC and/or AC power service, can
operate interconnected with or
independent of the utility grid, and can be
connected with other energy sources and
energy storage systems.1.7.1 Grid-
Connected (Utility-Interactive) PV Systems.
Diagram of grid-connected photovoltaic system
Types of PV Systems

Stand-alone PV systems are
designed to operate independent of
the electric utility grid, and are
generally designed and sized to
supply certain DC and/or AC electrical
loads.
These types of systems may be
powered by a PV array only, or may
use wind, an engine-generator or
utility power as an auxiliary power
source in what is called a PV-hybrid
system.
photovoltaic hybrid system.

The simplest type of stand-alone PV system is a direct-coupled system, where the DC
output of a PV module or array is directly connected to a DC load
Since there is no electrical energy storage (batteries) in direct-coupled systems, the load
only operates during sunlight hours, making these designs suitable for common applications
such as ventilation fans, water pumps, and small circulation pumps for solar thermal water
heating systems.
Matching the impedance of the electrical load to the maximum power output of the PV array
is a critical part of designing well-performing direct-coupled system.
For certain loads such as positive-displacement water pumps, a type of electronic DC-DC
converter, called a maximum power point tracker (MPPT) is used between the array and
load to help better utilize the available array maximum power output.
Direct-coupled PV system.

• Concentrating Solar
Thermal Plant (CSP)
It contains:
• Collector Field
• Turbine
• Generator
• Cooling Tower
• transformer

• Photovoltaic plants (PV)
It contains:
• Solar Arrays
• Inverter
• Transformer

• In both CSP and PV technologies, solar resources plays major
role.
• Maps are available to calculate solar resource of a particular
region. However, for both CSP and PV technologies different
solar radiations are taken into account.
• Basically two types of solar radiations are there:
• Global Horizontal Irradiations (GHI)
• Direct Normal Irradiation (DNI)
• For PV technologies GHI is considered. GHI consists of diffuse
radiations and direct horizontal radiations (beam).
Minimum GHI- 1000 kwh/m2
pa

• For CSP, DNI is considered.
DNI is the amount of
radiation received by a
surface which is
permanently aligned
perpendicular to the
incoming beam.
Minimum DNI- 1900 kwh/m2
pa

Sizing a PV System
Solar Panels
• Solar modules/panels are typically sold by the peak watt.
• That means that when the sun is at its peak intensity (clear day
around midday) of 1000 watts per m2,
• a solar module/panel rating at say 100 Wp (peak watts)
would put out 100 watts of power.
• The climate data at a given site summarizes the solar
intensity data in terms of peak sun hours,
• the effective number of hours that the sun is at that peak intensity
on an average day.
• If the average peak sun hours is 4.1, it also means that a kw
of PV panels will provide 4.1 kw-hr a day.

Sizing and Calculating
• To determine the number and size of the batteries
we will need, there are some thing we need to
determine,
• Load (number of kw being used),
• Battery capacity,
• Location of the panels,
• Type of mounting system,

Battery Sizing I
• If your load is 10 kw-hr per day, and you want to battery to
provide 2.5 days of storage, then it needs to store 25 kw-hr
of extractable electrical energy,
• Since deep cycle batteries can be discharged up to 80% of
capacity without harm, you need a battery with a storage of
25/0.8 = 31.25 kw-hr.
• A typical battery at 12 volts and 200 amp-hour capacity
stores 2.4 kw-hr of electrical energy.
• So how many batteries would you need?

Battery Sizing II
To calculate how many batteries:
• We use the relationship between battery energy (E) in kw-hr and
battery capacity (amp-hr),
• E(kw-hr) =capacity(amp-hr) x voltage/1000
• E = 200 amp-hr x 12 volts/1000= 2.4 kw-hr
• So for 31.25 kw-hr (2 ½ days) of storage we need
31.25 kw-hr/2.4 kw-hr/battery = 13 batteries
• How many batteries would you need for only one day of storage? 13/2.5 =
• 5.2 batteries
• If we are happy with one half day,
• we need only 2 or 3 batteries,

Example
• Typically, Landscape lights are rated at 20w,
• If we wanted to design a PV system to run these
lights for 30 days per charge how many batteries
would we need?
• 12 volt battery =
• E = 200 amp-hr x 12 volts/1000= 2.4 kw-hr
• Load = 20w x 30 days = 600w/1000 = .6 kw-hr
• .6 kw-hr/2.4 kw-hr = .25 batteries
• So how many batteries do we need?

Stand-alone inverters are connected to the battery bank
and supply AC power to a distribution panel that is
independent of the utility grid.

Interactive inverters are connected to the PV array and
supply AC power that is synchronized with the utility grid.

Solar Energy- Present
Scenario

Bio-fuel Energy

Bio-Fuel- Industry Overview
(India)
• Development of bio-fuels is yet at a nascent stage in India but
is being actively pursued to reduce India’s dependence on oil
imports.
• With 70% of crude oil requirement being met through imports, the
government is promoting use of bio-fuels.
• Bio-fuels primarily comprise of:
• Ethanol (made from sugarcane - molasses)
• Bio-diesel (made from Jatropha seeds)
• Bio-fuels has significant growth potential in India due to
government initiatives, mechanisms to expand production
capacity and minimize price fluctuations of key raw materials.

Production distribution of bio-
fuels

Bio-Fuel- Drivers & Challenges

Tidal energy

Tidal Energy - Introduction
• A form of hydropower that converts the energy of
tides into electricity or other useful forms of power.
• The first large-scale tidal power plant (the Rance
Tidal Power Station) started operation in 1966.
• Historically, tide mills have been used, both in
Europe and on the Atlantic coast of North America.

Tidal Energy – Technology
• There are basically two methodologies for creating
tidal power:
• by building semi-permeable barrages across estuaries
with a high tidal range to dam the water - barrages
allow tidal waters to fill an estuary via sluices and to
empty through turbines.
• by harnessing offshore tidal streams - tidal streams can
be harnessed using offshore underwater devices similar
to wind turbines.

Tidal Energy - India
• Since India is surrounded by sea on three sides, its potential to harness
tidal energy has been recognised by the Government of India.
• Potential sites for tidal power development have already been located. The
most attractive locations are the Gulf of Cambay and the Gulf of Kachchh
on the west coast where the maximum tidal range is 11 m and 8 m with
average tidal range of 6.77m and 5.23 m respectively.
• The Ganges Delta in the Sunderbans in West Bengal also has good locations
for small scale tidal power development. The maximum tidal range in
Sunderbans is approximately 5 m with an average tidal range of 2.97 m.
• The identified economic tidal power potential in India is of the order of
8000-9000 MW with about 7000 MW in the Gulf of Cambay about 1200
MW in the Gulf of Kachchh and less than 100 MW in Sundarbans.
• The Kachchh Tidal Power Project with an installed capacity of about 900
MW is estimated to cost about Rs.1460/- crore generating electricity at
about 90 paise per unit. The techno-economic feasibility report is now
being examined

• Tidal schedule vary from day to day since the orbit
moon does not occur on a regular 24 hours daily
schedule.
• Instead moon rotates around the earth every 24
hours 50 min. During this time tide raises and falls
twice, resulting in tidal cycle, which lasts for 12
hours 25 min.
• Tidal range = water elevation at high tide(A) –
water elevation at low tide (B).
• Rise and fall of water level follows a sinusoidal
curve. The average of time for water level to fall
from A to B approximately equal to 6 hours 12.5
min.

• During full moon, new moon when the sun, moon
and earth are approximately in one line, the
gravitational forces of sun & moon are at enhanced
level making high tides which are called spring
tides.
• Near first and third quarters of moon, the sun and
moon are at right angles to the earth, neap tides of
tidal range of small occur.
• Range varies during 29.5 day lunar month. It is max.
at the time of new and full moons (spring tide) and
the min. at the time of first and third quarter
moons (neap tide)

• A dam or sluice gate is placed across an ocean bay or estuary
(entry of water ways into the sea). An incoming tide fills up the
enclosed basin while passing through a row of hydraulic
turbines.
• After basin is filled with water, the gates are closed and the
turbines are shut down. The the turbine blades are reversed
and gates are opened again to let the water surge out. Thus
turbines would be rotated either way to generate electric
power.
• Tidal power plant involves construction of long barrier across
the bay to create a large basin on the land side. Barrier includes
dykes, gate controlled sluices & power house.
• Tidal power may have following different configurations
• Single basin, single effect tidal power scheme
• Single basin, double effect tidal power scheme
• Linked basin scheme S.PALANIVEL ASSOCIATE PROF./MECH. ENGG

• In the single basin, single effect tidal power scheme, the basin
is filled by keeping the sluices open and letting the water flow
from the sea to basin during high tide. Power is produced by
letting the water flow from the basin to the sea through the
turbines during low tide.
• In the single basin, double effect tidal power scheme, Power is
generated during the high tide with water flowing from the
sea to the basin through turbines also during low tide, with
water flowing from the basin to the sea through turbines. In
this case turbine blades should be reversible with proper blade
angle depending upon the direction of flow.
• In a linked basin (double basin single effect ) power scheme,
there are two basins on the land side with the power house
located in the barrier between two basins. Power is generated
by water flowing from high basin to low basin through turbines
and water flowing from low basin to sea during low tide

Geothermal Energy

• Geothermal energy is primarily from earth’s own interior.
• Natural heat in the earth has manifested itself for 1000 of
years in the form of volcanoes, lava flows, hot springs.
• The interior of earth is thought of consist of a central molten
core surrounded by a region of semi fluid material called
mantle, This is covered by the crust, which has a depth of 30 to
90 KM. Temp in the crust increases with the depth @ of 30
deg.C/KM
• Below the crust the molten mass called magma is in the
process of cooling at the rate of 0.063W/m2.The hot magma
near the surface (A) solidifies into igneous rock (B) or volcanic
rock.
• Ground water that finds its way down to this rock through
fissures in it will be heated by the heat of the rock or by mixing
with hot gases and steam emanating from magma.

• The heated water will then rise upward and into a porous and
permeable reservoir(C) above the igneous rock. This reservoir
is capped by a layer of impermeable solid rock (D) that raps
the hot water in the reservoir.
• The solid rock has fissures (E) that act as vents of the giant
underground boiler. The vents show up at the surface as
geysers, fumaroles (F) or hot springs(G).
• A well (H) tap steam from the fissur for use in a geo thermal
power palnt.
• Geothermal steam is of two kinds : magmatic steam that
originates from magma itself and meteoritic steam with
ground water heated by magma. The latter is the largest
source of geothermal steam.
• Not all geothermal sources produce steam, some are lower in
temp, so there will be only hot water, some receive no ground
water at all and contain only hot rock.

• Geothermal sources are three kinds
• 1. hydrothermal, 2.geopressurziedand 3.petrothermal
• Hydrothermal systems : these are those in which water is heated by contact
with hot rock which can be either vapor dominated or liquid dominated.
• In vapor dominated systems, the water is vaporised into steam that reaches
the surface in a relatively dry condition at about 200 deg.C and rarely above
8 bar. This steam is suitable for use in power plants with least cost. However
corrosive gases and erosive material are discouraging.
• In a liquid dominated systems, the hot water trapped underground is at a
temp. range of 174 to 315 deg.C. When trapped by wells drilled, the water
flows either naturally to the surface or pumped up to it. The drop in press. Is
about 8 bar or less causes it flash to a two phase mixture of low quality.
• It contains large concentrations of dissolved solids ranging from 3000 to
25000 ppm. Power production is adversely affected because these solids
precipitate and cause scaling in pipe and heat transfer areas.

• Geo pressurised Systems : These are sources of water or brine that has
been heated in a manner similar to hydrothermal water, except that
this water is trapped in much deeper underground aquifers (2400 m to
9100 m deep) at relatively low temp. (160 deg.C) and very high
pressure (> 1000 bar) with high salinity (H-10%) and is often referred as
brine.
• Also it is a saturated natural gas mostly methane, thought to be the
result of decomposition of organic matter.
• There is an economical feasibility of generating electricity by a
combined cycle, one that involves combustion of methane gas as well
as heat from the thermal energy of hot water.
• In petrothermal systems, magma lying close to earth’s surface heats
overlying rock and when underground water exists , there is simply hot
dry rock(HDR). This energy is called petrothermal energy. Since HDR is
largely impermeable, to make it permeable , fracturing methods are
considered which involves drilling wells into rock and fracturing by
high pressure water or nuclear explosives.

Geothermal Energy -
Introduction
• Sources of Earth’s Internal Energy 70% comes from
the decay of radioactive nuclei with long half lives
that are embedded within the Earth Some energy is
from residual heat left over from Earths formation.
The rest of the energy comes from meteorite
impacts.
• On average, the Earth emits 1/16 W/m 2 .
However, this number can be much higher in areas
such as regions near volcanoes, hot springs and
fumaroles

• Geothermal plants can be online 100%-90% of the
time. Coal plants can only be online 75% of the
time and nuclear plants can only be online 65% of
the time.
• Flash and Dry Steam Power Plants emit 1000x to
2000x less carbon dioxide than fossil fuel plants, no
nitrogen oxides and little SO2 . Binary and Hot Dry
Rock plants have no gaseous emission at all.
Geothermal plants do not require a lot of land,
400m2
can produce a gigawatt of energy over
30years.

• Produces 4 times the energy than they consume.
-initially costs more to install, but its maintenance
cost is 1/3 of the cost for a typical conventional
heating system and it decreases electric bill.
• This means that geothermal space heating will save
the consumer money.
• Electricity generated by geothermal plants saves 83.3
million barrels of fuel each year from being burned
world wide.
• This stops 49.6 tons of CO 2 from being emitted into
the atmosphere.

Bagasse

Introduction
• Bagasse is the fibrous matter that remains after
sugarcane or sorghum stalks are crushed to extract
their juice.
• It is currently used as a biofuel and as a renewable
resource in the manufacture of pulp and paper
products and building materials.

• Gujarat, being one of the leading sugarcane producer and
processor states, has the potential to set up Bagasse
base co-generation power plants for its sugar mills.
• The average cane crushing unit size in India is 2500 TCD
(Tons Cane crushing per Day), relatively much lower than
Brazil (9200 TCD) and Thailand (10300 TCD). However,
there are several units in Gujarat having capacity of more
than 5000 TCD.
• In fact some mills are having surplus Bagasse and
generating power for longer period than their own
requirement and are feeding this power to state power
supply grid and thereby generate additional income for
the unit.

• Bagasse from 1 ton cane crushing can produce 100
KwH of electricity. Normally, 2500 TCD project can
produce 2.5 MW of Electricity, after using Bagasse
as a fuel for steam generation in boiler.

WIND POWERPLANT LAYOUT

FUEL CELL
• Fuel Cell converts chemical energy directly into electrical
energy in a reaction that eliminates combustion.
• Performance of the Fuel cell is not restricted by second
law of thermodynamics.
• Negative ions or electrons flow from the cathode to the
anode within the device, so that the conventional current
flow from cathode to anode in the external circuit.
• The elemental particles referred as charge carriers. The
negative charge carriers may consist of electrons or
atoms or molecules of negative charges or electrons.
• The positive charge carriers may consist of atoms or
molecules that have lost some of their electrons or may
be an electron hole (space left by departure of electron)

• A Fuel cell could be considered as an electric battery in which
both the fuel and the oxidizer are continuously replaced.
• The anode and cathode material do not normally enter into
the chemical reactions although they act as catalysts.
• Two electrodes must also serve the function of preventing
the non-ionized fuel and oxidzer into the electrolyte between
the two.
• Fuel cells might be divided into basic categories according to
whether the product of the overall reaction must be
disposed of in the cathode plenum space or in the anode
plenum space and whether the current flow through the
electrolyte is a transfer of negative ions from the cathode to
anode or a transfer of positive ions in the opposite direction.
• Fuel cells are also classified according to the temp. at which
they operate.

• Fuel cells were originally used for manned space missions
where the hydrogen and oxygen were stored in their pure
form as liquids and the resulting combustion product, namely
water was then used by astronauts for drinking.
• For terrestrial uses, hydrogen containing gases or liquids as
the fuel at the anode and air containing oxygen at the cathode
are used. These type cells are cheaper but they are not as
efficient as using hydrogen and oxygen in pure form.
• Examples of hydro carbons ; methane CH4, ethane C2H6,
acetylene C2H4, propylene C3H6, propane C3H8, methanol,
CH3OH, hexane C6H14,butene C4H8, butane C4H10,pentane
C5H12, benzene C6H6, toluene C7H8,heptane C7H16, octane
C8H18, nonane C9H20, decane C10H22
• Nitrogenous : Ammonia NH3, hydrazine N2H4

• Hydro carbons are cracked with steam giving rise to CO, CO2
and H2. When H2 is blown through a porous metallic
electrode consisting of catalysts such as platinum and noble
metals, hydrogen molecule loses two electrons (2e-) and
becomes a doubly charged ion (2H+
). This is an oxidation
process.
• Because of electrons accumulating on the surface of the
metallic anode and electrolyte acquiring positively charged
ions adjacent to electrode, a charge separation occurs
resulting in a potential difference, positive on the electrolyte
side and negative on anode side.
• H+ ions pass through the electrolyte such as KOH, in which the
bond is ionic with K + and OH – ions being present. At the
cathode, electrons returning from the external circuit combine
with oxygen and react with water in KOH solution of the
electrolyte to form hydroxyl ions
• O2 + 4e–
+ 2H2O > 4OH– S.PALANIVEL ASSOCIATE PROF./MECH. ENGG

• The Oxygen in the above reaction suffers a reduction process
through combining with the electrons. These enter the
electrolyte and maintain the strength of the KOH, transporting
the electrons from cathode to the anode. The H+
and OH–
ions
combining to from H2
O and go into the solution.
• The electrodes must be good electrical conductors and highly
resistant to corrosive environment. They must also be catalytic
to perform charge separation, but not to take part in any
chemical reaction themselves.
• Because fuel cells work best with platinum and other precious
metals, nearly 25% of the cost of the cell is in these electrodes.
• The electrolyte is the carrier of charges and can be either acidic
or alkaline, and be in liquid or solid state.
• Regeneration in which the product materials can be re
converted to fuel and oxidant reduces costs.

Types of Fuel cells
• Phosphoric Acid Fuel cell (PAFC) : The cell operates at 200
deg.C, H2 & O2 cell, high pressure, efficient, 1 MW and above,
13.8 kV, platinum electro catalyst.
• Alkaline Fuel Cell (AFC) : H2 & O2 in pure form, KOH
electrolyte : electrodes porous Ni substrate with Pt support.
• Solid polymer Electrolyte Fuel cell (SPEFC) : It operates at
temp. below 100 deg C, high polymer electrolyte and Pt
electro catalyst.
• Molten carbon Fuel cell (MCFC) : It operates at high pressure
and temp. Electrolyte consists of molten carbonate of sodium
or potassium (NaCO3 or KCO3 Electrodes are made of Ni for
anode and Ag for the cathode
• Applications : 1. Electric power generation
• 2. peaking Power plants with stem plants operating as base
load plant and 3. automobiles and transport vehiclesS.PALANIVEL ASSOCIATE PROF./MECH. ENGG

Unit4 introduction to various renewable energy sources 0916

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