Distributed dispersed generation_J.B. Essuman

Distributed Generation and Technologies. Tech and Energy Group.
BY: Jones Bismark Essuman
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TABLE OF CONTENTS
1 DISTRIBUTED GENERATION (DG) ...................................................................................... 2
1.1 DG TECHOLOGIES.......................................................................................................... 2
2 RENEWABLE ENERGY TECHNOLOGIES............................................................................ 2
2.1 Solar Photovoltaic Systems ................................................................................................ 2
2.2 Wind Turbines ................................................................................................................... 3
2.3 Biomass ............................................................................................................................. 5
3 NON-RENEWABLE ENERGY TECHNOLOGIES .................................................................. 5
3.1 Micro-turbines ................................................................................................................... 5
3.2 Fuel Cells........................................................................................................................... 6
3.3 Combustion Gas turbines ................................................................................................... 6

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1 DISTRIBUTED GENERATION (DG)
Various bodies have defined distributed or dispersed generation in other forms but the
concept is similar. Generally, distributed generation is defined as electric power generation
that is connected directly to the distribution network at distribution level voltages or
connected to the customer side of the meter. There are quite a number of distributed
generation technologies. A few of these have been presented below.
1.1 DG TECHOLOGIES
DG technologies include both renewable and non-renewable energies.
Renewable energy sources include:
 Solar photovoltaic
 wind turbines
 Biomass, etc.
Non-renewable energy sources:
 Micro-turbines
 combustion gas turbines
 fuel cells, etc.
2 RENEWABLE ENERGY TECHNOLOGIES
2.1 Solar Photovoltaic Systems
Solar energy could be used to describe any phenomenon that is created by solar sources and
harnessed in the form of energy, directly or indirectly – from photosynthesis to photovoltaic.
Solar Photovoltaic (PV) refers that the energy from sunlight which is converted into DC
electricity using solar photovoltaic cells (PV cell). It is estimated that by 2050, PV
(photovoltaic) will provide around 11% of global electricity production and avoid 2.3
gigatonnes (Gt) of CO2 emissions per year
PV systems consist of several PV modules, which in turn consist of an array of several single
PV cells, connected together to achieve a higher output voltage. DC/DC converter is
employed to supply DC load or with DC/AC power inverter for AC load or at interface with
distribution grid. Maximum Power Point Tracking control is implemented to improve
efficiency. A typical grid-connected PV system is shown if figure 1

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Figure 1: Grid-Connected PV System.
PV systems have no moving parts, and thus require less maintenance and generate electricity
without producing CO2. Another advantage lies in its scalability: the efficiency of a system is
independent of the size of the installation. PV systems therefore are well suited both for small
installations on private houses as well as for large industrial installations .A typical West
African country has good solar PV potential. The northern part of Ghana receives fairly good
solar radiation in the range of 3.5-4.5 kWh/m2/day. This resource could supply electricity to
rural areas in the northern region where the solar potential is highest and the electrification
rate is the lowest in the country
2.2 Wind Turbines
Wind power is one of the renewable energy sources which has been widely developed in
recent years. The term wind energy or wind power is referred to the process by which the
wind is captured to generate electricity. About 1–2% of 174,423x109
kWh of energy that the
sun radiates to the earth per hour are converted into wind energy.Because of fairly constant
wind conditions, countries bordering a sea are well suited for wind harvesting.
Usage of wind Power is on the rise due some benefits enjoyed. These include: Wind-power
plants emit absolutely no CO2; The operation of wind turbines leaves behind no dangerous
residues as do other plants such as nuclear plants and Land occupied by wind farms can still
be used simultaneous for other purposes as agriculture.
The wind potential at the Ghana/Togo border (Volta Region) and along the coast of the Gulf
of Guinea is suitable for grid connected large wind farms while the scattered wind potential
can be exploited through stand-alone wind turbines.
The total wind energy potential of Ghana/Togo border is estimated at around 300 MW
capacity or 800 GWh electricity and the total potential along the coast of the Gulf of Guinea
is around 3000 MW capacity or 7,300 GWh.
Wind turbines require no fuel, no emissions, and produce DC power that needs AC/DC
inverters to be connected to the grid. The kinetic energy of wind is converted to mechanical
or electrical energy using wind turbines.

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The amount of energy captured by the rotor depends on the density of the air, the rotor area,
and the wind speed.
Wind turbines built today are either constant speed or variable speed wind turbines. Constant
speed turbines are directly coupled to the grid and run synchronously with the frequency of
the grid. These turbines run at a predefined speed and therefore reach their maximum
efficiency only for one wind speed, predefined by the rotor design.
Variable speed wind turbines became possible and efficient due to developments in power
electronics. Either a direct drive synchronous generator or a gear box and an induction
generator is applied to transform the wind energy into electrical energy.
Constant speed control is an easy and low-cost method, but variable speed brings the
following advantages
 Maximum power tracking for harnessing the highest possible energy from the wind,
 Lower mechanical stress,
 Less variations in electrical power, and
 Reduced acoustical noise at lower wind speeds.
Figure 2: Variable speed wind turbine with permanent magnet synchronous generator
(PMSG) controlled with a full-scale power converter.
WRSG: Wound Rotor Synchronous Generator, PMSG: Permanent Magnet Synchronous
Generator SCIG: Squirrel-Cage Induction Generator

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2.3 Biomass
Biomass energy is the conversion of biomass into useful forms of energy such as heat,
electricity and liquid fuels [Handbook of Renewable Energy Technology]. Biomass can be
vegetation trees, grasses, plants parts such as leaves, stems and twigs, sea weeds, and waste
products from various industries—including agriculture, forest products, transportation, and
construction—that dispose of large quantities of wood and plant products. Although biomass
contributes about 1,067 million tons oil equivalent (Mtoe) of energy worldwide, the
electricity generation from biomass is less than 2%.
3 NON-RENEWABLE ENERGY TECHNOLOGIES
3.1 Micro-turbines
Micro-turbines consist of basically: a compressor, a turbine generator, and a recuperator (or
heat exchanger). The voltage generated from micro-turbines cannot be coupled directly to the
utility; the output voltage must be rectified first using a diode rectifier to DC, then converted
back again to AC to synchronise with the utility grid. Micro-turbines run on natural gas,
landfill gas or on biogas
The main advantages of micro-turbines are: due to its small size their placement as DG
sources is not a problem making it easy to be installed to support electric demand in rural
areas. Micro-turbine generator has high efficiency performance with the low rate of
maintenance and low emissions produced, but on the other hand its disadvantage is the high
level of noise produced and the low efficiency
Figure 3: Micro-turbine

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3.2 Fuel Cells
Fuel cells are electrochemical devices that convert chemical energy from a fuel directly into
electrical energy by combining oxygen, as an oxidant, and hydrogen, as a fuel, without
combustion. Fuel cell plants are noiseless and pollution free. The average voltage of single
cell is 0.7V. Several cells are connected in series into stacks to increase the voltage to provide
the required voltage and power. With power electronic DC/DC converter and DC/AC
inverter, the generated DC voltage is controlled to enable for grid connection. Hydrogen is
the best fuel for these devices, however the security measures and the installation cost
associated with production, storage, transport, opens the door for the use of alternative fuels.
Apart from Hydrogen, it is also possible to use reformed natural gas, gasoline, methanol or
alcohol. However, fuel cells can only be considered as renewable DG if the used fuel were
produced with renewably generated energy.
Figure 4: Typical fuel cell principle
3.3 Combustion Gas turbines

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4 REFERENCES
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Distributed dispersed generation_J.B. Essuman

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