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3. TYPES OF DISTRIBUTED ENERGY RESOURCES

Distributed energy resource (DER) systems are small-scale power generation technologies

(typically in the range of 1 kW to 10,000 kW) used to provide an alternative to or an

enhancement of the traditional electric power system. The usual problem with distributed

generators is their high initial capital costs.

3.1 COGENERATION:

Distributed cogeneration sources use steam turbines, natural gas-fired fuel cells, Micro-

turbines or reciprocating engines to turn generators. The hot exhaust is then used for space or

water heating, or to drive an absorptive chiller for cooling such as air-conditioning. In

addition to natural gas-based schemes, distributed energy projects can also include other

renewable or low carbon fuels including bio fuels, biogas, landfill gas, sewage gas, coal bed

methane, syngas and associated petroleum gas.

In addition, molten carbonate fuel cell and solid oxide fuel cells using natural gas, such as the

ones from Fuel cell Energy and the Bloom energy server, or waste-to-energy are used as a

distributed energy resource.

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3.2 SOLAR PANEL:

A primary issue with solar power is that it is intermittent. Popular sources of power for

distributed generation are solar heat collection panels and solar panels on the roofs of

buildings or free-standing. Solar heating panels are used mostly for heating water and when

the water is heated into steam it can effectively and economically used in steam turbines to

produce electricity.

Some "thin-film" solar cells have waste-disposal issues when they are made with heavy

metals such as Cadmium telluride and Copper indium gallium selenide and must be recycled,

as opposed to silicon solar cells, which are mostly non-metallic. Unlike coal and nuclear,

there are no fuel costs, operating pollution, mining-safety or operating-safety issues. Solar

power has a low capacity factor, producing peak power at local noon each day. Average

capacity factor is typically 20%.

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3.3 WIND TURBINE:

Another source is small wind turbines. These have low maintenance, and low pollution,

however as with solar, wind energy is intermittent. Construction costs are higher than large

power plants, except in very windy areas. Wind towers and generators have substantial

insurable liabilities caused by high winds, but good operating safety. Wind also tends to

complement solar. Days without sun there tend to be windy, and vice versa. Many distributed

generation sites combine wind power and solar can be monitored online.

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3.4 WASTE-TO-ENERGY:

Municipal solid waste (MSW) and natural waste, such as sewage sludge, food waste and

animal manure will decompose and discharge methane-containing gas that can be collected as

used as fuel in gas turbines or micro turbines to produce electricity as a distributed energy

resource. Additionally, a California-based company has developed a process that transforms

natural waste materials, such as sewage sludge, into biofuel that can be combusted to power a

steam turbine that produces power. This power can be used in lieu of grid-power at the waste

source (such as a treatment plant, farm or dairy).

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3.5. FUEL CELLS:

There are many types of fuel cells currently under development in the 5-1000+ kW size

range, including phosphoric acid, proton exchange membrane, molten carbonate, solid oxide,

alkaline, and direct methanol.

Although the numerous types of fuel cells differ in their electrolytic material, they all use the

same basic principle. A fuel cell consists of two electrodes separated by an electrolyte.

Hydrogen fuel is fed into the anode of the fuel cell. Oxygen (or air) enters the fuel cell

through the cathode. With the aid of a catalyst, the hydrogen atom splits into a proton (H+)

and an electron. The proton passes through the electrolyte to the cathode and the electrons

travel in an external circuit. As the electrons flow through an external circuit connected as a

load they create a DC current. At the cathode, protons combine with hydrogen and oxygen,

producing water and heat. Fuel cells have very low levels of NOx and CO emissions because

the power conversion is an electrochemical process. The part of a fuel cell that contains the

electrodes and electrolytic material is called the "stack," and is a major contributor to the total

cost of the total system. Stack replacement is very costly but becomes necessary when

efficiency degrades as stack operating hours accumulate.

Fuel cells require hydrogen for operation. However, it is generally impractical to use

hydrogen directly as a fuel source; instead, it must be extracted from hydrogen-rich sources

such as gasoline, propane, or natural gas. Cost effective, efficient fuel reformers that can

convert various fuels to hydrogen are necessary to allow fuel cells increased flexibility and

commercial feasibility.

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3.6 RECIPROCATING DIESEL OR NATURAL GAS ENGINES:

Reciprocating engines, developed more than 100 years ago, were the first among DG

technologies. They are used on many scales, with applications ranging from fractional

horsepower units that power small tools to enormous 60 MW base load electric power plants.

Smaller engines are primarily designed for transportation and can usually be converted to power

generation with little modification. Larger engines are most frequently designed for power

generation, mechanical drive, or marine propulsion.

Reciprocating engines can be fueled by diesel or natural gas, with varying emission outputs.

Almost all engines used for power generation are four-stroke and operate in four cycles (intake,

compression, combustion, and exhaust). The process begins with fuel and air being mixed. In

turbocharged applications, the air is compressed before mixing with fuel. The fuel/air mixture is

introduced into the combustion cylinder and ignited with a spark. For diesel units, the air and fuel

are introduced separately with fuel being injected after the air is compressed. Reciprocating

engines are currently available from many manufacturers in all size ranges. They are typically

used for either continuous power or backup emergency power. Cogeneration configurations are

available with heat recovery from the gaseous exhaust.

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3.7MICROTURBINES:

Micro turbines are an emerging class of small-scale distributed power generation in the 30-400

kW size range. The basic technology used in micro turbines is derived from aircraft auxiliary

power systems, diesel engine turbochargers, and automotive designs. A number of companies are

currently field-testing demonstration units, and several commercial units are available for

purchase.

Micro turbines consist of a compressor, combustor, turbine, and generator. The compressors and

turbines are typically radial-flow designs, and resemble automotive engine turbochargers. Most

designs are single-shaft and use a high-speed permanent magnet generator producing variable

voltage, variable frequency alternating current (AC) power. Most micro turbine units are

designed for continuous-duty operation and are recuperated to obtain higher electric efficiencies.

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3.8 COMBUSTION GAS TURBINES:

Combustion turbines range in size from simple cycle units starting at about 1 MW to several

hundred MW when configured as a combined cycle power plant. Units from 1-15 MW are

generally referred to as industrial turbines (or sometimes as miniturbines), which differentiates

them both from larger utility grade turbines and smaller micro turbines.. Historically, they were

developed as aero derivatives, spawned from engines used for jet propulsion. Some, however, are

designed specifically for stationary power generation or compression applications in the oil and

gas industries. Multiple stages are typical and along with axial blading differentiate these turbines

from the smaller micro turbines described above.

Combustion turbines have relatively low installation costs, low emissions, and infrequent

maintenance requirements. Cogeneration DG installations are particularly advantageous when a

continuous supply of steam or hot water is desired.

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4. INTEGRATION WITH THE GRID

For reasons of reliability, distributed generation resources would be interconnected to the

same transmission grid as central stations. Various technical and economic issues occur in the

integration of these resources into a grid. Technical problems arise in the areas of power

quality, voltage stability, harmonics, reliability, protection, and control. Behavior of

protective devices on the grid must be examined for all combinations of distributed and

central station generation. A large scale deployment of distributed generation may affect grid-

wide functions such as frequency control and allocation of reserves. As a result smart grid

functions, virtual power plants and grid energy storage such as power to gas stations are

added to the grid.

5. BENEFITS OF DISTRIBUTED GENERATION

As mentioned above, basic tangible benefits that may be derived out of such sort of

distributed or dispersed or decentralized generation are the following.

• Easy and quicker installation on account of prefabricated standardized components

• Lowering of cost by avoiding long distance high voltage transmission

• Environment friendly where renewable sources are used

• Running cost more or less constant over the period of time with the use of renewable

sources

• Possibility of user-operator participation due to lesser complexity

• More dependability with simple construction, and consequent easy operation and

maintenance

Of course the issue of intermittent supply may be a big issue, particularly when backup

supply from grid does not exist. Initial cost too may be high depending upon location in a

number of cases.

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6. CONCLUSION

Distributed generation (DG) has much potential to improve distribution system performance.

The use of DG strongly contributes to a clean, reliable and cost effective energy for future.

The range of DG technologies and the variability in their size, performance, and suitable

applications suggest that DG could provide power supply solutions in many different

industrial, commercial, and residential settings. In this way, DG is contributing to improving

the security of electricity supply. However, distribution system designs and operating

practices are normally based on radial power flow and this creates a significant challenge for

the successful integration of DG system. As the issues are new and are the key for sustainable

future power supply, a lot of research is required to study their impact and exploit them to the

full extent.

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7. FUTURE SCOPE

Possible future methods include risk-based planning and advanced monitoring

schemes combined with curtailment of production and consumption.

Future generations of electric vehicles may have the ability to deliver power from the

battery in a vehicle-to-grid into the grid when needed. An electric vehicle network

could also be an important distributed generation resource.

The developed dynamic model of SOFC based DG system can be used along with

micro-turbine based DG system for combined operation to increase the efficiency of

the complete system.

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8. REFERENCES

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http://en.wikipedia.org/wiki/Distributed_generation

Distributed Generation - Basic Policy, Perspective Planning, and Achievement so far

in

India- Subrata Mukhopadhyay, Senior Member, IEEE, and Bhim Singh, Senior

member, IEEE.

Integration of Distributed Generation in the Power SystemBy Math H. Bollen,

Fainan Hassan

http://shodhganga.inflibnet.ac.in/bitstream/10603/2342/16/16_chapter%206.pdf