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PowerPedia:Distributed Generation

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migrogrid-flow.gif
Co-locating distributed energy resources with loads within the microgrid is
essential for realizing the full energy efficiency potential of distributed energy
resources through recovery of waste heat from electricity generation to building
end-uses. (Image from http://certs.lbl.gov/)

Distributed generation, also called On-site Generation, is a new trend in the generation of heat and electrical power. Distributed energy, or distributed generation, is a system in which electricity is produced at a large number of small to medium-sized power plants, rather than at one or more large capacity plants. This model decreases transmission distances, lowers the voltage needed for efficient transmission, and increases the resilience of a power grid. Its disadvantages include a loss of the economies of scale that large power plants may enjoy. Common technologies for distributed generation include small-scale wind or hydroelectric plants, or natural gas cycle plants. Renewable energy sources (or RES) capture their energy from existing flows of energy, from on-going natural processes, such as sunshine, wind, wave power, flowing water (hydropower), biological processes such as anaerobic digestion, and geothermal heat flow. These usually are essential in most distributed generations schemes.

Contents

Description

The Distributed Energy Resources (DER) concept permits "consumers" who are generating heat or electricity for their own needs to send surplus electrical power back into the power grid also know as net metering or share excess heat via a distributed heating grid. The electric power transmission grid usually transmits electricity to consumers. The term refers to the bulk transfer of electrical power from place to place. DER are autonomous generating, storage, and load control technologies that are typically located at customer premises and operated for the customer's benefit. They include microturbines, fuel cells, photovoltaic systems, and traditional internal combustion engines. CERTS is evaluating how these resources, when deployed in large numbers, affect and could be modified to enhance electricity grid reliability.

Distributed energy offers solutions to many of the nation's most pressing energy and electric power problems, including blackouts and brownouts, energy security concerns, power quality issues, tighter emissions standards, transmission bottlenecks, and the desire for greater control over energy costs. Distributed generation allow more reciprical relationship between the power companies and individuals. Typically, power transmission is between the power plant and a substation. Distributed generation systems with Combined Heat and Power (CHP) systems can be very efficient, using up to 90% of the fuel they consume. CHP can also save a lot of money and fuel. Estimates are that CHP has the potential to reduce the energy usage of the USA by up to 40%. Cogeneration (also combined heat and power or CHP) is the use of a power station to simultaneously generate both heat and electricity. Conventional power plants emit the heat created as a byproduct of electricity generation into the environment through cooling towers, as flue gas, or by other means. CHP captures the excess heat for domestic or industrial heating purposes, either very close to the plant, or - especially in eastern Europe - distributed through steam pipes to heat local housing ("district heating"). This steam can also be used for large air-conditioner units through turning a steam turbine connected to a compressor chilling water sent to the air handler units in a different building. Thermal power plants (including those that use fissile elements or burn coal, petroleum, or natural gas) do not convert all of their available energy into electricity, with the excess being wasted as excess heat. By capturing the excess heat, CHP allows a more total use of energy than conventional generation, potentially reaching an efficiency of 70-90%, compared with approximately 50% for the best conventional plants. This means that less fuel needs to be consumed to produce the same amount of useful energy.

CHP is most efficient when the heat can be used on site or very close to it. Overall efficiency is reduced when the heat must be transported over longer distances. This requires heavily insulated pipes, which are expensive and inefficient; whereas electricity can be transmitted along a comparatively simple wire, and over much longer distances for the same energy loss. Cogeneration plants are commonly found in district heating systems of big towns, universities, hospitals, hotels, prisons, oil refineries, paper mills, wastewater treatment plants, thermal enhanced oil recovery wells and industrial plants with large heating needs. Large or small, most cogeneration projects only produce, more or less, the amount of energy the facility requires. However, thermally enhanced oil recovery (TEOR) plants often produce a substantial amount of excess electricity. After generating electricity, these plants pump leftover steam into heavy oil wells so that the oil will flow more easily, increasing production. TEOR cogeneration plants in Kern County, California produce so much electricity that it cannot all be used locally and is transmitted to Los Angeles.

Large-scale market adoption of DER raises important issues about DER's impact on the grid's reliability. Specific areas that must be addressed include: control and dispatch strategies for DER; strategies to ensure the safety and protection of the grid; and the role of power electronic interfaces in connecting DER to the grid. Assessing grid reliability impacts requires a systems approach. A central concept in this research area is the microgrid, an interconnected network of DER that can function connected to or separate from the electricity grid. CERTS is investigating optimal microgrid designs, including the power electronics necessary to connect microgrids effectively to the power grid; conducting field tests of microgrid operation; and assessing the system reliability services that microgrids might provide.

der_1.jpg
Types of distributed energy resources and technologies
(Image from Distributed Energy Resources (DER), Barney L. Capehart)

Distributed energy programs boost cost-effective research and development aimed at lowering costs, reducing emissions, and improving reliability and performance to expand opportunities for the installation of distributed energy equipment today and in the future. Many factories, offices and especially hospitals require extremely reliable sources of electricity and heating for air conditioning and hot water. To safeguard their supply and reduce costs, some have installed co-generation or total energy plants, often using waste material, such as wood waste, or surplus heat from an industrial process to generate electricity. In some cases electricity is generated from a locally supplied fuel such as natural gas or diesel oil and the waste heat from the generator's thermal energy source is then used to provide hot water and industrial heating as well. It is often economic to have a co-generation plant when an industrial process requires a large amount of heat generated from non-electric sources such as fossil fuels or biomass.

Distributed energy technology
Small-scale, modular technologies for on-site, grid-connected or stand-alone energy conversion and delivery.
  • Gas-Fired Reciprocating Engines
  • Industrial Gas Turbines
  • Microturbines
  • Technology-Base Research
  • Thermally Activated Technologies
Integrated energy systems
Systems that combine distributed power generation with equipment that uses thermal energy to improve overall energy efficiency and fuel use.
  • CHP Applications
  • CHP Technologies

Regulatory and technological issues

Until recently, regulatory and technology issues meant that domestic consumer-generated electricity could not be easily or safely coupled with the incoming electric power supply. Electric companies need to have the ability to isolate parts of the power grid; when a line goes down workmen have to be sure the power is off before they work on it. They also spend much effort maintaining the quality of power in their grid. Distributed power installations can make control of these issues more difficult.

With the advent of extremely reliable power electronics it is becoming economic and safe to install even domestic scale co-generation equipment. These installations can produce domestic hot water, home heating and electricity, with surplus energy being sold back to the power company. Advances in electronics have eased the electric companies' safety and quality concerns. Regulators can act to remove barriers to the uptake of increased levels of distributed generation by ensuring centralized and distributed generation are operating on a 'level playing field'.

In the U.S., federal law requires that electric companies buy power from independent producers, subject to regulations and insurance coverage. Distributed generation is not confined to fossil fuel. Some countries and regions already have a significant renewable power source in power grid-tied wind turbines and biomass combustion. Increasing amounts of distributed generation will require changes in the technology required to manage transmission and distribution of electricity. There will be an increasing need for network operators to manage networks 'actively' rather than 'passively' as is currently the case. Increased active management will bring additional benefits for consumers in terms of the introduction of greater choice with regard to energy supply services and greater competition. However, the switch to more active management may be a difficult one. Distribution networks are a natural monopoly and are thus tightly regulated to ensure that they do not draw excess profits at the expense of the consumer. Network investment is a key determinant of the costs that networks can pass on to consumers.

Networks act to maximise their profits within the framework provided by their regulation. Currently such regulation does not lend itself very well to incentivising innovative behaviour by networks. This is likely to prove to be a barrier both to the development of networks and to increases in the levels of distributed generation that is added to networks. However there are indications that regulatory authorities are becoming more aware of the potential barriers and are introducing regulation of connection charges and conditions to enable distributed generators to participate in the electricity market. Ofgem, the gas and electricity regulator in Britain has also introduced incentives for electricity Distribution Network Operators (DNOs) who spend on research and development of innovative network solutions to accommodate distributed generation.

While there is the potential for a major portion of the electrical power supply to come from decentralized power sources, significant issues remain limiting the widespread use of this technology, including billing and energy credits, generation control and system stability. To maintain control and stability of the power system in some networks, the neighbouring consumers need to consume all the electric power that a producing consumer may produce. This ensures there is a net flow of electric power from generators to consumers in the distribution network, even though there may be a local outflow within the local distribution. With the growth of electricity markets and the requirement for open access to networks, the distributed generator may have more options for selling the excess production, either through physical or financial contracts (Hedges).

External articels and references

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Web
Sites on On-site Generation
via Google Search
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Image
Images of Distributed Generation
via Google Image
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groups
Newsgroups with Distributed Generation
via Google Groups
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Web
Sites on On-site Generation
via Google Search
G
Image
Images of On-site Generation
via Google Image
G
groups
Newsgroups with On-site+Generation
via Google Groups
Y
Image
Images of Distributed Generation
via Yahoo! Images
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Image
Images of On-site Generation
via Yahoo! Images
General references
Decentralized power sources
Inverters - 230V/115V grid tied or off grid
Resources
Other

See also

GRID FOOTER

GRID PROBLEMS

GRID SOLUTIONS

Energy conversion methods and theories   Edit
Active solar | Anaerobic digestion | Barra system | Biomass | Blue energy | Deep lake water cooling | Distributed generation | Earth cooling tubes | Electricity generation | Energy Tower | Fuel cell | Fusion power | Geothermal power | Hydroelectricity | Hydrogen production | Mechanical biological treatment | Microgeneration | Ocean thermal energy conversion | Passive solar | Photovoltaics | Seasonal thermal store | Solar cell | Solar panel | Solar pond | Solar power | Solar power tower | Solar thermal energy | Solar tracker | Solar updraft tower | Sustainable community energy system | Tidal power | Trombe wall | Water turbine | Wave power | Wind farm | Wind power | Wind turbine

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