Distributed generation

Distributed generation

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Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 from many small energy sources.

Currently, industrial countries generate most of their electricity in large centralized facilities, such as fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, gas powered
Combined cycle
In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

), nuclear
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

, large solar power plants or hydropower
Hydropower, hydraulic power, hydrokinetic power or water power is power that is derived from the force or energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as...

 plants. These plants have excellent economies of scale, but usually transmit electricity long distances and negatively affect the environment.

Economies of scale

Most plants are built this way due to a number of economic
An economy consists of the economic system of a country or other area; the labor, capital and land resources; and the manufacturing, trade, distribution, and consumption of goods and services of that area...

, health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...

 & safety
Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...

, logistical
Logistics is the management of the flow of goods between the point of origin and the point of destination in order to meet the requirements of customers or corporations. Logistics involves the integration of information, transportation, inventory, warehousing, material handling, and packaging, and...

, environmental, geographical
Geography is the science that studies the lands, features, inhabitants, and phenomena of Earth. A literal translation would be "to describe or write about the Earth". The first person to use the word "geography" was Eratosthenes...

 and geological
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

For example, coal power plants are built away from cities to prevent their heavy air pollution from affecting the populace. In addition, such plants are often built near collieries to minimize the cost of transporting coal. Hydroelectric
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 plants are by their nature limited to operating at sites with sufficient water flow. Most power plants are often considered to be too far away for their waste heat to be used for heating buildings.

Low pollution is a crucial advantage of combined cycle plants that burn natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

. The low pollution permits the plants to be near enough to a city to be used for district heating
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...

 and cooling.

Localised generation

Distributed generation is another approach. It reduces the amount of energy lost in transmitting electricity because the electricity is generated very near where it is used, perhaps even in the same building. This also reduces the size and number of power lines that must be constructed.

Typical distributed power sources in a Feed-in Tariff
Feed-in Tariff
A feed-in tariff is a policy mechanism designed to accelerate investment in renewable energy technologies. It achieves this by offering long-term contracts to renewable energy producers, typically based on the cost of generation of each technology...

 (FIT) scheme have low maintenance, low pollution and high efficiencies. In the past, these traits required dedicated operating engineers and large complex plants to reduce pollution. However, modern embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...

s can provide these traits with automated operation and renewables
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

, such as sunlight, wind and geothermal
Geothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...

. This reduces the size of power plant that can show a profit.

Distributed energy resources

Distributed energy resource (DER) systems are small-scale power generation technologies (typically in the range of 3 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 are their high costs.

One popular source is solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s on the roofs of buildings. The production cost is $0.99 to 2.00/W (2007) plus installation and supporting equipment unless the installation is Do it yourself
Do it yourself
Do it yourself is a term used to describe building, modifying, or repairing of something without the aid of experts or professionals...

 (DIY) bringing the cost to $5.25 to 7.50 (2010). This is comparable to coal power plant costs of $0.582 to 0.906/W (1979), adjusting for inflation. Nuclear power is higher at $2.2 to $6.00/W (2007). Some solar cells ("thin-film" type) also have waste disposal issues, since "thin-film" type solar cells often contain heavy-metal electronic wastes, such as Cadmium telluride
Cadmium telluride
Cadmium telluride is a crystalline compound formed from cadmium and tellurium. It is used as an infrared optical window and a solar cell material. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell...

 (CdTe) and Copper indium gallium selenide
Copper indium gallium selenide
Copper indium gallium selenide is a I-III-VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide and copper gallium selenide...

 (CuInGaSe), and need to be recycled. As opposed to silicon semi-conductor type solar cells which is made from quartz. The plus side is that unlike coal and nuclear, there are no fuel costs, pollution, mining safety or operating safety issues. Solar also has a low duty cycle
Duty cycle
In engineering, the duty cycle of a machine or system is the time that it spends in an active state as a fraction of the total time under consideration....

, producing peak power at local noon each day. Average duty cycle is typically 20%.

Another source is small wind turbines
Wind generator
A wind generator is a device that generates electrical power from wind energy.Wind generators have traditionally been wind turbines, i.e. a propeller attached to an electric generator attached to appropriate electronics to attach it to the electrical grid or to charge batteries.Recently, however, a...

. These have low maintenance, and low pollution. Construction costs are higher ($0.80/W, 2007) per watt 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. In some areas of the US there may also be Property Tax costs involved with wind turbines that are not offset by incentives or accelerated depreciation
Accelerated depreciation
Accelerated depreciation refers to any one of several methods by which a company, for 'financial accounting' or tax purposes, depreciates a fixed asset in such a way that the amount of depreciation taken each year is higher during the earlier years of an asset’s life...

. Wind also tends to be complementary to solar; on days there is no sun there tends to be wind and vice versa. Many distributed generation sites combine wind power and solar power such as Slippery Rock University, which can be monitored online.

In addition, solid oxide fuel cells using natural gas, such as the Bloom Energy Server
Bloom Energy Server
The Bloom Energy Server is a solid oxide fuel cell made by Bloom Energy, of Sunnyvale, California, that can use a wide variety of inputs to generate electricity on the site where it will be used.It is highly efficient, low cost and has lower polluting emissions...

, have recently become a distributed energy resource.

Distributed cogeneration
Cogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat....

 sources use natural gas-fired microturbines or reciprocating engine
Reciprocating engine
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

s to turn generators. The hot exhaust is then used for space or water heating, or to drive an absorptive chiller  for air-conditioning. The clean fuel has only low pollution. Designs currently have uneven reliability, with some makes having excellent maintenance costs, and others being unacceptable.

Cost factors

Cogenerators are also more expensive per watt than central generators. They find favor because most buildings already burn fuels, and the cogeneration can extract more value from the fuel.

Some larger installations utilize combined cycle generation. Usually this consists of a gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 whose exhaust boils water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 for a steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

 in a Rankine cycle
Rankine cycle
The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is...

. The condenser of the steam cycle provides the heat for space heating or an absorptive chiller. Combined cycle plants with cogeneration have the highest known thermal efficiencies, often exceeding 85%.

In countries with high pressure gas distribution, small turbines can be used to bring the gas pressure to domestic levels whilst extracting useful energy. If the UK were to implement this countrywide an additional 2-4 GWe would become available. (Note that the energy is already being generated elsewhere to provide the high initial gas pressure - this method simply distributes the energy via a different route.)

Future generations of electric vehicles will have the ability to deliver power from the battery into the grid when needed. An electric vehicle network
Electric vehicle network
An electric vehicle network is a proposed infrastructure system of publicly accessible charging stations and possibly battery swap stations to recharge electric vehicles....

 could also be an important distributed generation resource.


A microgrid is a localized grouping of electricity generation, energy storage, and loads that normally operates connected to a traditional centralized grid (macrogrid). This single point of common coupling with the macrogrid can be disconnected. The microgrid can then function autonomously. Generation and loads in a microgrid are usually interconnected at low voltage. From the point of view of the grid operator, a connected microgrid can be controlled as if it was one entity. Microgrid generation resources can include fuel cells, wind, solar, or other energy sources. The multiple dispersed generation sources and ability to isolate the microgrid from a larger network would provide highly reliable electric power. Byproduct heat from generation sources such as microturbines could be used for local process heating or space heating, allowing flexible trade off between the needs for heat and electric power.

Modes of power generation

DER systems may include the following devices/technologies:
  • Combined heat power (CHP)
  • Fuel cells
  • Micro combined heat and power
    Micro combined heat and power or micro-CHP is an extension of the now well established idea of cogeneration to the single/multi family home or small office building.- Overview :...

  • Microturbines
  • Photovoltaic Systems
  • Reciprocating engines
  • Small Wind power
    Wind power
    Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

  • Stirling engines

Communication in DER systems

  • IEC 61850-7-420 is under development as a part of IEC 61850 standards which deals with the complete object models as required for DER systems. It uses communication services mapped to MMS
    Manufacturing Message Specification
    Manufacturing Message Specification is an international standard dealing with messaging system for transferring real time process data and supervisory control information between networked devices and/or computer applications. The standard is developed and maintained by the ISO Technical...

     as per IEC 61850-8-1 standard.

  • OPC
    OLE for process control
    OLE for Process Control , which stands for Object Linking and Embedding for Process Control, is the original name for a standards specification developed in 1996 by an industrial automation industry task force...

     is also used for the communication between different entities of DER system.

Legal requirements for distributed generation

In 2010 Colorado enacted a law requiring that by 2020 that 3% of the power generated in Colorado utilize distributed generation of some sort.

See also

  • Autonomous building
    Autonomous building
    An autonomous building is a building designed to be operated independently from infrastructural support services such as the electric power grid, gas grid, municipal water systems, sewage treatment systems, storm drains, communication services, and in some cases, public roads.Advocates of...

  • Demand response
    Demand response
    In electricity grids, demand response is similar to dynamic demand mechanisms to manage customer consumption of electricity in response to supply conditions, for example, having electricity customers reduce their consumption at critical times or in response to market prices...

  • Energy harvesting
    Energy harvesting
    Energy harvesting is the process by which energy is derived from external sources , captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.Energy harvesters...

  • Electric power transmission
    Electric power transmission
    Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...

  • Electricity generation
    Electricity generation
    Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

  • Electricity market
    Electricity market
    In economic terms, electricity is a commodity capable of being bought, sold and traded. An electricity market is a system for effecting purchases, through bids to buy; sales, through offers to sell; and short-term trades, generally in the form of financial or obligation swaps. Bids and offers use...

  • Electricity retailing
    Electricity retailing
    Electricity retailing is the final process in the delivery of electricity from generation to the consumer. The other main processes are transmission and distribution.- Beginnings :...

  • Energy demand management
    Energy demand management
    Energy demand management, also known as demand side management , is the modification of consumer demand for energy through various methods such as financial incentives and education...

  • Future energy development
  • Green power superhighway
  • Grid-tied electrical system
    Grid-tied electrical system
    A grid-tied electrical system, also called tied to grid or grid tie system, is a semi-autonomous electrical generation or grid energy storage system which links to the mains to feed excess capacity back to the local mains electrical grid...

  • Hydrogen station
    Hydrogen station
    A hydrogen station is a storage or filling station for hydrogen, usually located along a road or hydrogen highway, or at home as part of the distributed generation resources concept. The stations are usually intended to power vehicles, but can also be used to power small devices. Vehicles use...

  • IEEE 1547
    IEEE 1547
    IEEE 1547 is a standard of the Institute of Electrical and Electronics Engineers meant to provide a set of criteria and requirements for the interconnection of distributed generation resources into the power grid in the United States.-Purpose:"This document provides a uniform standard for...

     Standard for Interconnecting Distributed Resources with Electric Power Systems
  • Islanding
    Islanding refers to the condition in which a distributed generation generator continues to power a location even though electrical grid power from the electric utility is no longer present. Islanding can be dangerous to utility workers, who may not realize that a circuit is still powered, and it...

  • Microgeneration
    Microgeneration is the small-scale generation of heat and power by individuals, small businesses and communities to meet their own needs, as alternatives or supplements to traditional centralized grid-connected power...

  • Microgrid
  • Net metering
    Net metering
    Net metering is an electricity policy for consumers who own renewable energy facilities or V2G electric vehicles. "Net", in this context, is used in the sense of meaning "what remains after deductions" — in this case, the deduction of any energy outflows from metered energy inflows...

  • Relative cost of electricity generated by different sources
  • Renewable energy development
  • Smart meter
    Smart meter
    A smart meter is usually an electrical meter that records consumption of electric energy in intervals of an hour or less and communicates that information at least daily back to the utility for monitoring and billing purposes. Smart meters enable two-way communication between the meter and the...

  • Smart power grid
    Smart Power Grid
    A smart grid is a digitally enabled electrical grid that gathers, distributes, and acts on information about the behavior of all participants in order to improve the efficiency, reliability, economics, and sustainability of electricity services.Smart grid policy is organized in Europe as Smart...

  • Solar Guerrilla
  • Stand-alone power system
    Stand-alone power system
    A stand-alone power system , also known as remote area power supply , is an off-the-grid electricity system for locations that are not fitted with an electricity distribution system...

  • Sustainable community energy system
    Sustainable community energy system
    A sustainable community energy system is an integrated approach to supplying a local community with its energy requirements from renewable energy or high-efficiency co-generation energy sources...

  • Trigeneration
    Trigeneration, also called CCHP , refers to the simultaneous generation of electricity, useful heating and useful cooling from the same original heat source such as fuel or solar energy...

  • Vehicle-to-grid
    Vehicle-to-grid describes a system in which plug-in electric vehicles, such as electric cars and plug-in hybrids , communicate with the power grid to sell demand response services by either delivering electricity into the grid or by throttling their charging rate.Vehicle-to-grid can be used with...

  • Virtual power plant
    Virtual power plant
    A virtual power plant is a cluster of distributed generation installations which are collectively run by a central control entity....

  • World Alliance for Decentralized Energy
    World Alliance for Decentralized Energy
    The World Alliance for Decentralized Energy was founded in 1997 with the original name of the International Cogeneration Alliance. It was originally formed in response to the UNFCCC meetings in Kyoto to raise the profile of cogeneration on the agenda...

  • External links