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[[File:Cogeneration.png|thumb|350px]]
{{Sustainable energy}}
'''Cogeneration''' or '''combined heat and power''' ('''CHP''') is the use of a [[heat engine]]<ref>[http://www.clarke-energy.com/chp-cogeneration/ Cogeneration and Cogeneration Schematic] {{webarchive|url=https://web.archive.org/web/20131209230320/http://www.clarke-energy.com/chp-cogeneration/ |date=2013-12-09 }}, www.clarke-energy.com, retrieved 26.11.11</ref> or [[power station]] to [[electricity generation|generate electricity]] and [[Heat|useful heat]] at the same time. '''Trigeneration''' or '''combined cooling, heat and power''' ('''CCHP''') refers to the simultaneous generation of electricity and useful heating and cooling from the combustion of a fuel or a solar heat collector. The terms ''cogeneration'' and ''trigeneration'' can be also applied to the power systems generating simultaneously electricity, heat, and industrial chemicals – e.g., [[syngas]] or pure [[hydrogen]] (article: [[combined cycle]]s, chapter: [[Combined cycle#Natural gas integrated power & syngas (hydrogen) generation cycle|natural gas integrated power & syngas (hydrogen) generation cycle]]).

Cogeneration is a more efficient use of fuel because otherwise-wasted heat from electricity generation is put to some productive use. Combined heat and power (CHP) plants recover otherwise wasted [[thermal energy]] for [[HVAC#heating|heating]]. This is also called combined heat and power district heating. Small CHP plants are an example of [[Distributed generation|decentralized energy]].<ref>{{cite web|url=http://www.dekb.co.uk/home/index.php?option=com_content&view=category&id=82&Itemid=93|title=What is Decentralised Energy?|publisher=The Decentralised Energy Knowledge Base|url-status=live|archiveurl=https://web.archive.org/web/20081210123230/http://www.dekb.co.uk/home/index.php?option=com_content&view=category&id=82&Itemid=93|archivedate=2008-12-10}}</ref> By-product heat at moderate temperatures (100–180&nbsp;°C, 212–356&nbsp;°F) can also be used in [[absorption refrigerator]]s for cooling.

The supply of high-temperature heat first drives a [[gas turbine|gas]] or [[steam turbine]]-powered generator. The resulting low-temperature waste heat is then used for water or space heating. At smaller scales (typically below 1 MW) a [[gas engine]] or [[diesel engine]] may be used. Trigeneration differs from cogeneration in that the [[waste heat]] is used for both heating and cooling, typically in an absorption refrigerator. Combined cooling, heat and power systems can attain higher overall efficiencies than cogeneration or traditional power plants. In the United States, the application of trigeneration in buildings is called building cooling, heating and power. Heating and cooling output may operate concurrently or alternately depending on need and system construction.

Cogeneration was practiced in some of the earliest installations of electrical generation. Before central stations distributed power, industries generating their own power used exhaust steam for process heating. Large office and apartment buildings, hotels and stores commonly generated their own power and used waste steam for building heat. Due to the high cost of early purchased power, these CHP operations continued for many years after utility electricity became available.<ref>{{cite book
|title=A History of Industrial Power in the United States, 1730-1930, Vol. 3: The Transmission of Power
|last =Hunter
|first=Louis C.
|authorlink=
|author2=Bryant, Lynwood
|year =1991
|publisher =MIT Press
|location =Cambridge, Massachusetts, London
|isbn =978-0-262-08198-6
|page =}}</ref>

==Overview==
[[File:Masnedø power station.jpg|300px|thumb|right|[[Masnedø]] CHP power station in [[Denmark]]. This station burns straw as fuel. The adjacent greenhouses are heated by [[district heating]] from the plant.]]

Many process industries, such as chemical plants, oil refineries and pulp and paper mills, require large amounts of process heat for such operations as chemical reactors, distillation columns, steam driers and other uses. This heat, which is usually used in the form of steam, can be generated at the typically low pressures used in heating, or can be generated at much higher pressure and passed through a turbine first to generate electricity. In the turbine the steam pressure and temperature is lowered as the internal energy of the steam is converted to work. The lower pressure steam leaving the turbine can then be used for process heat.<!--[[Thermal power plants]] (those that are based on a [[thermodynamic cycle]] to convert heat produced from [[Concentrated solar power|solar mirrors]], [[uranium|fissile elements]], burning [[coal]], [[petroleum]], or [[natural gas]]), and [[heat engine]]s in general, do not convert all of their thermal energy into electricity. In most heat engines, more than half is lost as excess [[heat]] (see: [[Second law of thermodynamics]] and [[Carnot's theorem (thermodynamics)|Carnot's theorem]]). By capturing the excess heat, CHP uses heat that would be wasted in a conventional [[power plant]], potentially reaching an [[thermal efficiency|efficiency]] of up to 80%.<ref>{{cite web|url=http://www1.eere.energy.gov/industry/distributedenergy/pdfs/chp_report_12-08.pdf|title=Combined Heat and Power – Effective Energy Solutions for a Sustainable Future|publisher=Oak Ridge National Laboratory |accessdate=9 September 2011 |date=1 December 2008}}</ref> This means that less fuel needs to be consumed to produce the same amount of useful energy.-->

Steam turbines at [[thermal power station]]s are normally designed to be fed high pressure steam, which exits the turbine at a condenser operating a few degrees above ambient temperature and at a few millimeters of mercury absolute pressure. (This is called a ''condensing'' turbine.) For all practical purposes this steam has negligible useful energy before it is condensed. Steam turbines for cogeneration are designed either for ''extraction'' of some steam at lower pressures after it has passed through a number of turbine stages, with the un-extracted steam going on through the turbine to a condenser. In this case, the extracted steam causes a mechanical [[power loss factor|power loss]] in the downstream stages of the turbine. Or they are designed, with or without extraction, for final exhaust at ''back pressure'' (non-condensing).<ref>{{cite web|url=https://www.nrel.gov/docs/fy04osti/36924.pdf|title=Consider Installing High-Pressure Boilers With Back Pressure Turbine-Generators|website=nrel.gov|accessdate=28 April 2018|url-status=live|archiveurl=https://web.archive.org/web/20161221120102/http://www.nrel.gov/docs/fy04osti/36924.pdf|archivedate=21 December 2016}}</ref><ref name="Steam-its generation and use">{{cite book
|title=Steam-its generation and use |url=https://archive.org/details/steamitsgenerat00compgoog |last= |first= |authorlink= |year= |publisher =Babcock & Wilcox |location= |isbn= |pages=}}</ref> The extracted or exhaust steam is used for process heating. Steam at ordinary process heating conditions still has a considerable amount of [[enthalpy]] that could be used for power generation, so cogeneration has an opportunity cost.

A typical power generation turbine in a [[paper mill]] may have extraction pressures of 160 psig (1.103 MPa) and 60 psig (0.41 MPa). A typical back pressure may be 60 psig (0.41 MPa). In practice these pressures are custom designed for each facility. Conversely, simply generating process steam for industrial purposes instead of high enough pressure to generate power at the top end also has an opportunity cost (See: [[Steam turbine#Steam supply and exhaust conditions|Steam supply and exhaust conditions]]). The capital and operating cost of high pressure boilers, turbines and generators are substantial. This equipment is normally operated [[Continuous production|continuously]], which usually limits self-generated power to large-scale operations.

[[File:Metz biomass power station.jpg|thumb|left|A cogeneration plant in [[Metz]], [[France]]. The 45MW boiler uses waste wood [[biomass]] as energy source, and provides electricity and heat for 30,000 [[dwelling]]s.]]

A [[combined cycle]] (in which several thermodynamic cycles produce electricity), may also be used to extract heat using a heating system as [[Condenser (heat transfer)|condenser]] of the power plant's [[bottoming cycle]]. For example, the RU-25 [[MHD generator]] in [[Moscow]] heated a boiler for a conventional steam powerplant, whose condensate was then used for space heat. A more modern system might use a [[gas turbine]] powered by [[natural gas]], whose exhaust powers a steam plant, whose condensate provides heat. Cogeneration plants based on a combined cycle power unit can have thermal efficiencies above 80%.

The viability of CHP (sometimes termed utilisation factor), especially in smaller CHP installations, depends on a good baseload of operation, both in terms of an on-site (or near site) electrical demand and heat demand. In practice, an exact match between the heat and electricity needs rarely exists. A CHP plant can either meet the need for heat (''heat driven operation'') or be run as a [[power plant]] with some use of its waste heat, the latter being less advantageous in terms of its utilisation factor and thus its overall efficiency. The viability can be greatly increased where opportunities for trigeneration exist. In such cases, the heat from the CHP plant is also used as a primary energy source to deliver cooling by means of an [[absorption chiller]].

CHP is most efficient when 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.

A car engine becomes a CHP plant in winter when the reject heat is useful for warming the interior of the vehicle. The example illustrates the point that deployment of CHP depends on heat uses in the vicinity of the heat engine.

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]]{{Citation needed|date=February 2007}}.

CHP is one of the most cost-efficient methods of reducing carbon emissions from heating systems in cold climates <ref>{{cite web|url=http://www.claverton-energy.com/carbon-footprints-of-various-sources-of-heat-chpdh-comes-out-lowest.html|title=Carbon footprints of various sources of heat – biomass combustion and CHPDH comes out lowest|publisher=Claverton Energy Research Group|url-status=dead|archiveurl=https://web.archive.org/web/20111005102349/http://www.claverton-energy.com/carbon-footprints-of-various-sources-of-heat-chpdh-comes-out-lowest.html|archivedate=2011-10-05}}</ref> and is recognized to be the most energy efficient method of transforming energy from fossil fuels or biomass into electric power.<ref>{{cite web|url=http://www.viessmann.co.uk/en/industry/combined-heat-and-power-generation/chp-units.html|title=Cogeneration recognized to be the most energy efficient method of transforming energy|publisher=Viessmann|url-status=live|archiveurl=https://web.archive.org/web/20160808225555/http://www.viessmann.co.uk/en/industry/combined-heat-and-power-generation/chp-units.html|archivedate=2016-08-08}}</ref> 
Cogeneration plants are commonly found in [[district heating]] systems of cities, [[central heating]] systems of larger buildings (e.g. hospitals, hotels, prisons) and are commonly used in the industry in thermal production processes for process water, cooling, steam production or [[Carbon dioxide|CO<sub>2</sub>]] fertilization.

==Types of plants==
Topping cycle plants primarily produce electricity from a steam turbine. Partly expanded steam is then condensed in a heating condensor at a temperature level that is suitable e.g. [[district heating]] or [[water desalination]].

[[Bottoming cycle]] plants produce high temperature heat for industrial processes, then a [[waste heat recovery unit|waste heat recovery]] boiler feeds an electrical plant. Bottoming cycle plants are only used in industrial processes that require very high temperatures such as furnaces for glass and metal manufacturing, so they are less common.

Large cogeneration systems provide heating water and power for an industrial site or an entire town. Common CHP plant types are:
* [[Gas turbine]] CHP plants using the waste heat in the flue gas of gas turbines. The fuel used is typically [[natural gas]].
* [[Gas engine]] CHP plants use a reciprocating gas engine which is generally more competitive than a gas turbine up to about 5 MW. The gaseous fuel used is normally [[natural gas]]. These plants are generally manufactured as fully packaged units that can be installed within a plantroom or external plant compound with simple connections to the site's gas supply, electrical distribution network and heating systems. Typical outputs and efficiences see <ref>{{cite web|url=http://www.claverton-energy.com/finning-caterpillar-gas-engine-chp-ratings-and-thermal-outputs.html|title=Finning Caterpillar Gas Engine CHP Ratings|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20150518094951/http://www.claverton-energy.com/finning-caterpillar-gas-engine-chp-ratings-and-thermal-outputs.html|archivedate=18 May 2015}}</ref> Typical large example see <ref>{{cite web|url=http://www.claverton-energy.com/first-energy-offer-excellent-condition-complete-gas-engined-chp-system-for-sale-and-installation.html|title=Complete 7 MWe Deutz ( 2 x 3.5MWe) gas engine CHP power plant for sale|publisher=Claverton Energy Research Group|url-status=live|archiveurl=https://web.archive.org/web/20130930042456/http://www.claverton-energy.com/first-energy-offer-excellent-condition-complete-gas-engined-chp-system-for-sale-and-installation.html|archivedate=2013-09-30}}</ref>
* [[Biofuel|Biofuel engine]] CHP plants use an adapted reciprocating gas engine or [[diesel engine]], depending upon which biofuel is being used, and are otherwise very similar in design to a Gas engine CHP plant. The advantage of using a biofuel is one of reduced [[hydrocarbon fuel]] consumption and thus reduced carbon emissions. These plants are generally manufactured as fully packaged units that can be installed within a plantroom or external plant compound with simple connections to the site's electrical distribution and heating systems. Another variant is the [[wood gasifier]] CHP plant whereby a wood pellet or wood chip biofuel is [[gasified]] in a zero oxygen high temperature environment; the resulting gas is then used to power the gas engine. Typical smaller size biogas plant see <ref name="claverton-energy.com">{{cite web|url=http://www.claverton-energy.com/38-hhv-caterpillar-bio-gas-engine-fitted-to-long-reach-sewage-works.html|title=38% HHV Caterpillar Bio-gas Engine Fitted to Sewage Works - Claverton Group|accessdate=15 May 2015|url-status=dead|archiveurl=https://archive.is/20130102053132/http://www.claverton-energy.com/38-hhv-caterpillar-bio-gas-engine-fitted-to-long-reach-sewage-works.html|archivedate=2 January 2013}}</ref>
* [[Combined cycle]] power plants adapted for CHP
* [[Molten-carbonate fuel cell]]s and [[solid oxide fuel cell]]s have a hot exhaust, very suitable for heating.
* [[Steam turbine]] CHP plants that use the heating system as the [[steam]] condenser for the steam turbine.
* [[Nuclear power]] [[Nuclear power plant|plants]], similar to other steam turbine power plants, can be fitted with extractions in the turbines to bleed partially expanded steam to a heating system. With a heating system temperature of 95&nbsp;°C it is possible to extract about 10 MW heat for every MW electricity lost. With a temperature of 130&nbsp;°C the gain is slightly smaller, about 7 MW for every MWe lost.<ref>http://www.elforsk.se/nyhet/seminarie/Elforskdagen%20_10/webb_varme/d_welander.pdf{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }} [swedish]</ref> A review of cogeneration options is in <ref>{{Cite journal|last=Locatelli|first=Giorgio|last2=Fiordaliso|first2=Andrea|last3=Boarin|first3=Sara|last4=Ricotti|first4=Marco E.|date=2017-05-01|title=Cogeneration: An option to facilitate load following in Small Modular Reactors|journal=Progress in Nuclear Energy|volume=97|pages=153–161|doi=10.1016/j.pnucene.2016.12.012|url=http://eprints.whiterose.ac.uk/110233/1/Load%20Following%20by%20Cogeneration%20V27%20to%20deposit.pdf}}</ref>

Smaller cogeneration units may use a [[reciprocating engine]] or [[Stirling engine]]. The heat is removed from the exhaust and radiator. The systems are popular in small sizes because small gas and diesel engines are less expensive than small gas- or oil-fired steam-electric plants.

Some cogeneration plants are fired by [[biomass]],<ref>{{cite web|url=http://www.opet-chp.net/download/wp3/iisalmifinland.pdf|title=High cogeneration performance by innovative steam turbine for biomass-fired CHP plant in Iislami, Finland|publisher=OPET|accessdate=13 March 2011|url-status=live|archiveurl=https://web.archive.org/web/20110715113827/http://www.opet-chp.net/download/wp3/iisalmifinland.pdf|archivedate=15 July 2011}}</ref> or industrial and [[municipal solid waste]] (see [[incineration]]). Some CHP plants utilize waste gas as the fuel for electricity and heat generation. Waste gases can be gas from [[animal waste]], [[landfill gas]], [[Firedamp|gas from coal mines]], [[sewage gas]], and combustible industrial waste gas.<ref>{{cite journal|title=Transforming Greenhouse Gas Emissions into Energy|journal=WIPO Green Case Studies, 2014|date=2014|url=http://www.wipo.int/edocs/pubdocs/en/wipo_pub_951_3.pdf|accessdate=6 April 2015|publisher=World Intellectual Property Organization|url-status=live|archiveurl=https://web.archive.org/web/20150413090614/http://www.wipo.int/edocs/pubdocs/en/wipo_pub_951_3.pdf|archivedate=13 April 2015}}</ref>

Some cogeneration plants combine gas and solar [[photovoltaic]] generation to further improve technical and environmental performance.<ref>{{cite journal | last1 = Oliveira | first1 = A.C. | last2 = Afonso | first2 = C. | last3 = Matos | first3 = J. | last4 = Riffat | first4 = S. | last5 = Nguyen | first5 = M. | last6 = Doherty | first6 = P. | year = 2002 | title = A Combined Heat and Power System for Buildings driven by Solar Energy and Gas | doi = 10.1016/S1359-4311(01)00110-7 | journal = Applied Thermal Engineering | volume = 22 | issue = 6| pages = 587–593 }}</ref> Such hybrid systems can be scaled down to the building level<ref>{{cite journal | last1 = Yagoub | first1 = W. | last2 = Doherty | first2 = P. | last3 = Riffat | first3 = S. B. | year = 2006 | title = Solar energy-gas driven micro-CHP system for an office building | url = | journal = Applied Thermal Engineering | volume = 26 | issue = 14| pages = 1604–1610 | doi=10.1016/j.applthermaleng.2005.11.021}}</ref> and even individual homes.<ref name="Energy">{{cite journal | last1 = Pearce | first1 = J. M. | year = 2009 | title = Expanding Photovoltaic Penetration with Residential Distributed Generation from Hybrid Solar Photovoltaic + Combined Heat and Power Systems | url = | journal = Energy | volume = 34 | issue = 11| pages = 1947–1954 | doi = 10.1016/j.energy.2009.08.012 | citeseerx = 10.1.1.593.8182 }}</ref>

===MicroCHP===
[[Micro combined heat and power]] or 'Micro cogeneration" is a so-called [[Distributed Energy Resource|distributed energy resource]] (DER). The installation is usually less than 5 [[Watt#Electrical and thermal watts|kW<sub>e</sub>]] in a house or small business. Instead of burning fuel to merely heat space or water, some of the energy is converted to electricity in addition to heat. This electricity can be used within the home or business or, if permitted by the grid management, sold back into the electric power grid.

Delta-ee consultants stated in 2013 that with 64% of global sales the fuel cell micro-combined heat and power passed the conventional systems in sales in 2012.<ref>[http://www.fuelcelltoday.com/media/1889744/fct_review_2013.pdf The fuel cell industry review 2013] {{webarchive|url=https://web.archive.org/web/20160414152813/http://www.fuelcelltoday.com/media/1889744/fct_review_2013.pdf |date=2016-04-14 }}</ref> 20.000 units were sold in [[Japan]] in 2012 overall within the Ene Farm project. With a [[Service life|Lifetime]] of around 60,000 hours. For [[PEM fuel cell]] units, which shut down at night, this equates to an estimated lifetime of between ten and fifteen years.<ref name="fuelcelltoday.com">{{cite web|url=http://www.fuelcelltoday.com/analysis/analyst-views/2013/13-02-27-latest-developments-in-the-ene-farm-scheme|title=Latest Developments in the Ene-Farm Scheme|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20160414152815/http://www.fuelcelltoday.com/analysis/analyst-views/2013/13-02-27-latest-developments-in-the-ene-farm-scheme|archivedate=14 April 2016}}</ref> For a price of $22,600 before installation.<ref>{{cite web|url=http://panasonic.co.jp/corp/news/official.data/data.dir/2013/01/en130117-5/en130117-5.html|title=Launch of New 'Ene-Farm' Home Fuel Cell Product More Affordable and Easier to Install - Headquarters News - Panasonic Newsroom Global|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20140710072943/http://panasonic.co.jp/corp/news/official.data/data.dir/2013/01/en130117-5/en130117-5.html|archivedate=10 July 2014}}</ref> For 2013 a state subsidy for 50,000 units is in place.<ref name="fuelcelltoday.com"/>

MicroCHP installations use five different technologies: [[microturbines]], [[internal combustion]] engines, [[stirling engine]]s, closed cycle [[steam engine]]s and [[fuel cell]]s. One author indicated in 2008 that MicroCHP based on Stirling engines is the most cost effective of the so-called microgeneration technologies in abating carbon emissions;<ref>{{cite web|url=http://www.claverton-energy.com/what-is-microgeneration.html|title=What is Microgeneration? And what is the most cost effective in terms of CO2 reduction|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20150711112424/http://www.claverton-energy.com/what-is-microgeneration.html|archivedate=11 July 2015}}</ref> A 2013 UK report from Ecuity Consulting stated that MCHP is the most cost-effective method of utilising gas to generate energy at the domestic level.<ref>[http://www.ecuity.com/wp-content/uploads/2013/03/The-role-of-micro-CHP-in-a-smart-energy-world.pdf The role of micro CHP in a smart energy world] {{webarchive|url=https://web.archive.org/web/20160304072549/http://www.ecuity.com/wp-content/uploads/2013/03/The-role-of-micro-CHP-in-a-smart-energy-world.pdf |date=2016-03-04 }}</ref><ref>{{cite web|url=http://www.renewableenergyfocus.com/view/31489/micro-chp-report-powers-heated-discussion-about-uk-energy-future/|title=Micro CHP report powers heated discussion about UK energy future|author=Elsevier Ltd, The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20160320101136/http://www.renewableenergyfocus.com/view/31489/micro-chp-report-powers-heated-discussion-about-uk-energy-future/|archivedate=20 March 2016}}</ref> however, advances in reciprocation engine technology are adding efficiency to CHP plant, particularly in the biogas field.<ref>{{cite web|url=http://www.alfagy.com/|title=Best Value CHP, Combined Heat & Power and Cogeneration - Alfagy - Profitable Greener Energy via CHP, Cogen and Biomass Boiler using Wood, Biogas, Natural Gas, Biodiesel, Vegetable Oil, Syngas and Straw|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20150423020535/http://alfagy.com/|archivedate=23 April 2015}}</ref> As both MiniCHP and CHP have been shown to reduce emissions <ref>{{cite journal | last1 = Pehnt | first1 = M | year = 2008 | title = Environmental impacts of distributed energy systems—The case of micro cogeneration | url = | journal = Environmental Science & Policy | volume = 11 | issue = 1| pages = 25–37 | doi=10.1016/j.envsci.2007.07.001}}</ref> they could play a large role in the field of CO<sub>2</sub> reduction from buildings, where more than 14% of emissions can be saved using CHP in buildings.<ref>{{cite web |url=http://alfagy.com/what-is-chp/133-kaarsberg-t-rfiskum-jromm-a-rosenfeld-j-koomey-and-wpteagan-1998-qcombined-heat-and-power-chp-or-cogeneration-for-saving-energy-and-carbon-in-commercial-buildingsq.html |title=Buying CHP and Cogeneration - the Process - Alfagy CHP & Cogeneration |accessdate=2012-11-03 |url-status=live |archiveurl=http://archive.wikiwix.com/cache/20121103154812/http://alfagy.com/what-is-chp/133-kaarsberg-t-rfiskum-jromm-a-rosenfeld-j-koomey-and-wpteagan-1998-qcombined-heat-and-power-chp-or-cogeneration-for-saving-energy-and-carbon-in-commercial-buildingsq.html |archivedate=2012-11-03 }} "Combined Heat and Power (CHP or Cogeneration) for Saving Energy and Carbon in Commercial Buildings."</ref> The University of Cambridge reported a cost effective steam engine MicroCHP prototype in 2017 which has the potential to be commercially competitive in the following decades.<ref>{{cite journal | last1 = Du | first1 = Ruoyang | last2 = Robertson | first2 = Paul | year = 2017 | title = Cost Effective Grid-Connected Inverter for a Micro Combined Heat and Power System | journal = IEEE Transactions on Industrial Electronics | volume =  64| issue =  7| pages =  5360–5367| doi = 10.1109/TIE.2017.2677340 | url = https://www.repository.cam.ac.uk/handle/1810/263361 }}</ref> Quite recently, in some private homes, [[Micro combined heat and power#Fuel cells|fuel cell micro-CHP plants]] can now be found, which can operate on hydrogen, or other fuels as natural gas or LPG.<ref>[http://www.pace-energy.eu/micro-cogeneration/ Fuel Cell micro CHP]</ref><ref>[https://www.cogeneurope.eu/events/past-events/cogen-event/fuel-cell-micro-cogeneration-generating-sustainable-heat-and-power-for-your-home Fuel cell micro Cogeneration]</ref> When running on natural gas, it relies on [[Methane reformer|steam reforming]] of natural gas to convert the natural gas to hydrogen prior to use in the fuel cell. This hence still emits CO2 (see reaction) but (temporarily) running on this can be a good solution until the point where the hydrogen is starting to be become distributed through the (natural gas) piping system.

===Trigeneration===
[[File:Trigeneration Cycle.jpg|300px|thumb|right|Trigeneration cycle]]
A plant producing electricity, heat and cold is called a trigeneration<ref>{{cite web|url=http://www.clarke-energy.com/gas-engines/trigeneration/%7ctitle=Trigeneration|title=Clarke Energy - Fuel-Efficient Distributed Generation|work=Clarke Energy|accessdate=15 May 2015}}{{dead link|date=April 2018 |bot=SheriffIsInTown |fix-attempted=yes }}</ref> or polygeneration plant. Cogeneration systems linked to [[absorption chiller]]s or adsorption chillers use waste heat for [[refrigeration]].<ref>[http://www.fchea.org/core/import/PDFs/CHP%20Fact%20Sheet.pdf Fuel Cells and CHP] {{webarchive |url=https://web.archive.org/web/20120518094954/http://www.fchea.org/core/import/PDFs/CHP%20Fact%20Sheet.pdf |date=May 18, 2012 }}</ref>

===Combined heat and power district heating===
{{See also|District heating}}

In the [[United States]], [[Consolidated Edison]] distributes 66 billion kilograms of 350&nbsp;°F (180&nbsp;°C) steam each year through its seven cogeneration plants to 100,000 buildings in [[Manhattan]]—the biggest steam district in the United States. The peak delivery is 10 million pounds per hour (or approximately 2.5 GW).<ref>{{cite web| title =Newsroom: Steam| publisher =ConEdison| url =http://www.coned.com/newsroom/energysystems_steam.asp| accessdate =2007-07-20| url-status =live| archiveurl =https://web.archive.org/web/20070821132012/http://www.coned.com/newsroom/energysystems_steam.asp| archivedate =2007-08-21}}</ref><ref>{{cite web| last =Bevelhymer| first =Carl| title =Steam| publisher =Gotham Gazette| date =2003-11-10| url =http://www.gothamgazette.com/article/issueoftheweek/20031110/200/674| accessdate =2007-07-20| url-status =live| archiveurl =https://web.archive.org/web/20070813013416/http://www.gothamgazette.com/article/issueoftheweek/20031110/200/674| archivedate =2007-08-13}}</ref>

===Industrial CHP===
Cogeneration is still common in [[pulp and paper mill]]s, refineries and chemical plants. In this "industrial cogeneration/CHP", the heat is typically recovered at higher temperatures (above 100 deg C) and used for process steam or drying duties. This is more valuable and flexible than low-grade waste heat, but there is a slight loss of power generation. The increased focus on [[sustainability]] has made industrial CHP more attractive, as it substantially reduces [[carbon footprint]] compared to generating steam or burning fuel on-site and importing electric power from the grid.

====Utility pressures versus self generated industrial====
Industrial cogeneration plants normally operate at much lower boiler pressures than utilities. Among the reasons are: 1) Cogeneration plants face possible contamination of returned condensate. Because boiler feed water from cogeneration plants has much lower return rates than 100% condensing power plants, industries usually have to treat proportionately more boiler make up water. Boiler feed water must be completely oxygen free and de-mineralized, and the higher the pressure the more critical the level of purity of the feed water.<ref name="Steam-its generation and use"/> 2) Utilities are typically larger scale power than industry, which helps offset the higher capital costs of high pressure. 3) Utilities are less likely to have sharp load swings than industrial operations, which deal with shutting down or starting up units that may represent a significant percent of either steam or power demand.

===Heat recovery steam generators===
A [[heat recovery steam generator]] (HRSG) is a steam boiler that uses hot [[exhaust gas]]es from the [[gas turbine]]s or [[reciprocating engine]]s in a CHP plant to heat up water and generate [[steam]]. The steam, in turn, drives a [[steam turbine]] or is used in industrial processes that require heat.

HRSGs used in the CHP industry are distinguished from conventional steam generators by the following main features:
* The HRSG is designed based upon the specific features of the gas turbine or reciprocating engine that it will be coupled to.
* Since the exhaust gas temperature is relatively low, heat transmission is accomplished mainly through [[convection]].
* The exhaust gas velocity is limited by the need to keep head losses down. Thus, the transmission coefficient is low, which calls for a large heating surface area.
* Since the temperature difference between the hot gases and the fluid to be heated (steam or water) is low, and with the heat transmission coefficient being low as well, the evaporator and economizer are designed with plate fin heat exchangers.

==Cogeneration using biomass==

[[Biomass]] is emerging as one of the most important sources of [[renewable energy]]. Biomass refers to any plant or animal matter in which it is possible to be reused as a source of heat or electricity, such as [[sugarcane]], vegetable oils, wood, organic waste and residues from the food or agricultural industries. Brazil is now considered a world reference in terms of energy generation from biomass.<ref>{{cite thesis |type=Dissertação |degree=Mestrado em Ciência e Engenharia de Materiais |last=Soares Teixeira |first=Ronaldo |title=. Utilização de resíduos sucro-alcooleiros na fabricação de fibrocimento pelo processo de extrusão |publisher= Universidade de São Paulo |year=2010 |language=pt}}</ref>

A growing sector in the use of biomass for power generation is the sugar and alcohol sector, which mainly uses sugarcane bagasse as fuel for [[thermal]] and [[electric power]] generation  <ref>{{cite web |url= http://www.epe.gov.br/pt/publicacoes-dados-abertos/publicacoes/balanco-energetico-nacional-2018 |title= Balanço energético nacional 2018 |publisher=Empresa de Pesquisa Energética |accessdate=11 March 2019}}.</ref>

===Power cogeneration in the sugar and alcohol sector===

In the sugarcane industry, cogeneration is fuelled by the [[bagasse]] residue of sugar refining, which is burned to produce steam. Some steam can be sent through a [[turbine]] that turns a generator, producing electric power.<ref>{{cite thesis |type=Dissertação |degree=Mestrado |last=Dantas Filho|first=Paulo Lucas |title=. Análise da Viabilidade Econômica Financeira de Projetos de Cogeração de Energia Através do Bagaço de Cana-de-Açúcar em Quatro Usinas em São Paulo |publisher= Universidade de São Paulo |year=2009 |language=pt}}</ref>

Energy cogeneration in sugarcane industries located in Brazil is a practice that has been growing in last years. With the adoption of energy cogeneration in the sugar and alcohol sector, the sugarcane industries are able to supply the electric energy demand needed to operate, and generate a surplus that can be commercialized.<ref>{{cite thesis |type=Dissertação |degree=Graduação |last=Barbeli | first=Marcelo Carlos |title=. A cogeração de energia e sua importância do ponto de vista técnico, econômico e ambiental |publisher= Faculdade de Tecnologia, Ciências e Educação - FATECE |year=2015 |language=pt}}</ref><ref>{{cite journal|author = Tomaz W. L, Gordono F. S, Da Silva F. P, De Castro M. D. C, Esperidião M. |title= Cogeração de energia a partir do bagaço da cana-de-açúcar: estudo de caso múltiplo no setor sucroalcoleiro | date= 2015}}</ref>

===Advantages of the cogeneration using sugarcane bagasse===

In comparison with the electric power generation by means of fossil fuel-based [[thermoelectric]] plants, such as [[natural gas]], the energy generation using sugarcane bagasse has environmental advantages due to the reduction of [[CO2]] emissions.<ref name="RefA">{{cite thesis |type=Dissertação |degree=Mestrado |last=Ribeiro |first=Silvio |title= Gestão ambiental em usinas do setor sucroalcooleiro: fatores de influência e práticas adotadas |publisher= Universidade Estadual Paulista (UNESP) de Bauru  |year=2010 |language=pt}}</ref>

In addition to the environmental advantages, cogeneration using sugarcane bagasse presents advantages in terms of efficiency comparing to thermoelectric generation, through the final destination of the energy produced. While in thermoelectric generation, part of the heat produced is lost, in cogeneration this heat has the possibility of being used in the production processes, increasing the overall efficiency of the process.<ref name="RefA"/>

===Disadvantages of the cogeneration using sugarcane bagasse===

In sugarcane cultivation, is usually used potassium source's containing high concentration of [[chlorine]], such as [[potassium chloride]] (KCl). Considering that KCl is applied in huge quantities, sugarcane ends up absorbing high concentrations of chlorine.<ref name="RefB">{{cite journal|author = Yive, N. S . C. K., Tiroumalechetty, M. |title= Dioxin levels in fly ash coming from the combustion of bagasse |journal= Journal of Hazardous Materials  | volume = 155 |issue= 1–2 |pages= 179–182 |date= 2008|doi= 10.1016/j.jhazmat.2007.11.045 }}</ref>

Due to this absorption, when the sugarcane bagasse is burned in the power cogeneration, dioxins <ref name="RefB"/> and methyl chloride <ref name="RefC">{{cite journal |url=http://www.indiapost.gov.in/Pdf/Customs/List_of_Psychotropic_Substances.pdf |title= Global chlorine emissions from biomass burning: Reactive Chlorine Emissions Inventory |journal= Journal of Geophysical Research: Atmospheres |volume= 104 |pages= 8373–8389 |last= Lobert |first1= Jurgen |last2= Keene |first2=Willian |last3= Yevich |first3=Jennifer |publisher= http://onlinelibrary.wiley.com/doi/10.1029/1998JD100077/pdf |accessdate=11 March 2019|doi= 10.1029/1998JD100077 |year= 1999 }}</ref> ends up being emitted. In the case of dioxins, these substances are considered very toxic and cancerous.<ref>{{cite journal|author = Agency for Toxic Substances and Disease Registry (ATSDR) |title= Public health statement chlorinated dibenzo-p-dioxins (CDDs)|date= 1998}}</ref><ref>{{cite journal|author = XU, J., YE, Y., HUANG, F., CHEN, H., WU, HAN., HUANG, J., HU, J., XIA, D., WU, Y |title= Association between dioxin and cancer incidence and mortality: a meta analysis |journal= Scientific Reports  | volume = 6 |date= 2016 |doi=10.1038/srep38012}}</ref><ref>{{cite web |url=http://www.ejnet.org/dioxin/|title= Dioxins & Furans: The Most Toxic Chemicals Known to Science|editor= Environmental Justice Activists |accessdate=5 March 2019}}</ref>

In the case of methyl chloride, when this substance is emitted and reaches the [[stratosphere]], it ends up being very harmful for the [[ozone]] layer, since chlorine when combined with the ozone molecule generates a catalytic reaction leading to the breakdown of ozone links.<ref name="RefC"/>

After each reaction, chlorine starts a destructive cycle with another ozone molecule. In this way, a single chlorine atom can destroy thousands of ozone molecules. As these molecules are being broken, they are unable to absorb the [[ultraviolet rays]]. As a result, the [[UV radiation]] is more intense on Earth and there is a worsening of [[global warming]].<ref name="RefC"/>

==Comparison with a heat pump==
A [[heat pump]] may be compared with a CHP unit as follows. If, to supply thermal energy, the exhaust steam from the turbo-generator must be taken at a higher temperature than the system would produce most electricity at, the lost electrical generation is ''as if'' a heat pump were used to provide the same heat by taking electrical power from the generator running at lower output temperature and higher efficiency.<ref>{{cite web|url=http://www.orchardpartners.co.uk/Docs/IAEEVilniusPaperWhyHeatFromCHPisRenewableMarginalExergyAnalysis2011-09-14.pdf|title=Why Heat From CHP is Renewable - based on paper presented at IAEE Vilnius (2010)|date=2011-09-14|accessdate=2017-12-25|page=4 paragraph 4|url-status=live|archiveurl=https://web.archive.org/web/20170921204903/http://www.orchardpartners.co.uk/Docs/IAEEVilniusPaperWhyHeatFromCHPisRenewableMarginalExergyAnalysis2011-09-14.pdf|archivedate=2017-09-21}}</ref> Typically for every unit of electrical power lost, then about 6 units of heat are made available at about 90&nbsp;°C. Thus CHP has an effective [[Coefficient of performance|Coefficient of Performance (COP)]] compared to a heat pump of 6.<ref>{{Cite journal | doi = 10.1016/j.enpol.2011.05.007| title = Combined heat and power considered as a virtual steam cycle heat pump| year = 2011| last1 = Lowe | first1 = R. | journal = Energy Policy| volume = 39| issue = 9| pages = 5528–5534}}</ref> However, for a remotely operated heat pump, losses in the electrical distribution network would need to be considered, of the order of 6%. Because the losses are proportional to the square of the current, during peak periods losses are much higher than this and it is likely that widespread (i.e. citywide application of heat pumps) would cause overloading of the distribution and transmission grids unless they were substantially reinforced.

It is also possible to run a heat driven operation combined with a heat pump, where the excess electricity (as heat demand is the defining factor on utilization) is used to drive a heat pump. As heat demand increases, more electricity is generated to drive the heat pump, with the waste heat also heating the heating fluid.

==Distributed generation==
Most industrial countries generate the majority of their electrical power needs in large centralized facilities with capacity for large electrical power output. These plants benefit from economy of scale, but may need to transmit electricity across long distances causing transmission losses. Cogeneration or trigeneration production is subject to limitations in the local demand, and thus may sometimes need to reduce e.g. heat or cooling production to match the demand. An example of cogeneration with trigeneration applications in a major city is the [[New York City steam system]].

==Thermal efficiency==
Every heat engine is subject to the theoretical efficiency limits of the [[Carnot cycle]] or subset [[Rankine cycle]] in the case of steam turbine power plants or [[Brayton cycle]] in gas turbine with steam turbine plants. Most of the efficiency loss with steam power generation is associated with the [[Enthalpy of vaporization|latent heat of vaporization]] of steam that is not recovered when a turbine exhausts its low temperature and pressure steam to a condenser. (Typical steam to condenser would be at a few millimeters absolute pressure and on the order of 5&nbsp;°C/11&nbsp;°F hotter than the cooling water temperature, depending on the condenser capacity.) In cogeneration this steam exits the turbine at a higher temperature where it may be used for process heat, building heat or cooling with an [[absorption chiller]]. The majority of this heat is from the [[Enthalpy of vaporization|latent heat of vaporization]] when the steam condenses.

[[Thermal efficiency]] in a cogeneration system is defined as:

:<math>\eta_{th} \equiv \frac{W_{out}}{Q_{in}} \equiv \frac{\text{Electrical power output + Heat output}}{\text{Total heat input}}</math>

Where:
:<math>\eta_{th}</math> = Thermal efficiency
:<math>W_{out}</math> = Total work output by all systems
:<math>Q_{in}</math> = Total heat input into the system

Heat output may be used also for cooling (for example in Summer), thanks to an absorption chiller.
If cooling is achieved in the same time, [[Thermal efficiency]] in a trigeneration system is defined as:

:<math>\eta_{th} \equiv \frac{W_{out}}{Q_{in}} \equiv \frac{\text{Electrical power output + Heat output + Cooling output}}{\text{Total heat input}}</math>

Where:
:<math>\eta_{th}</math> = Thermal efficiency
:<math>W_{out}</math> = Total work output by all systems
:<math>Q_{in}</math> = Total heat input into the system

Typical cogeneration models have losses as in any system. The energy distribution below is represented as a percent of total input energy:<ref>{{cite web|title=Trigeneration Systems with Fuel Cells|url=http://www.icrepq.com/icrepq-08/245-san-martin.pdf|work=Research Paper|accessdate=18 April 2011|url-status=live|archiveurl=https://web.archive.org/web/20111006064857/http://www.icrepq.com/icrepq-08/245-san-martin.pdf|archivedate=6 October 2011}}</ref>
:Electricity = 45%
:Heat + Cooling = 40%
:Heat losses = 13%
:Electrical line losses = 2%

Conventional central coal- or nuclear-powered power stations convert about 33-45% of their input heat to electricity.<ref name="energy.gov">{{cite web|url=http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |title=DOE – Fossil Energy: How Turbine Power Plants Work |publisher=Fossil.energy.gov |accessdate=2011-09-25 |url-status=dead |archiveurl=https://web.archive.org/web/20100527095840/http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |archivedate=May 27, 2010 }}</ref><ref name="Steam-its generation and use"/>  [[Brayton cycle]] power plants operate at up to 60% efficiency. In the case of conventional power plants approximately 10-15% of this heat is lost up the stack of the boiler, most of the remaining heat emerges from the turbines as low-grade waste heat with no significant local uses so it is usually rejected to the environment, typically to cooling water passing through a condenser.<ref name="Steam-its generation and use"/> Because turbine exhaust is normally just above ambient temperature, some potential power generation is sacrificed in rejecting higher temperature steam from the turbine for cogeneration purposes.<ref>See Mechanical or Chemical Engineering texts on Thermodynamics.</ref>

For cogeneration to be practical power generation and end use of heat must be in relatively close proximity (<2&nbsp;km typically).
Even though the efficiency of a small distributed electrical generator may be lower than a large central power plant, the use of its waste heat for local heating and cooling can result in an overall use of the primary fuel supply as great as 80%.<ref name="energy.gov"/> This provides substantial financial and environmental benefits.

==Costs==
{{See also|Cost of electricity by source}}
Typically, for a gas-fired plant the fully installed cost per kW electrical is around £400/kW (US$577), which is comparable with large central power stations.<ref name="claverton-energy.com"/>

==History==

===Cogeneration in Europe===
[[File:Power plant at sunset.jpg|thumb|220px|A cogeneration thermal power plant in [[Ferrera Erbognone]] ([[Province of Pavia|PV]]), [[Italy]]]]

The [[European Union|EU]] has actively incorporated cogeneration into its energy policy via the [[CHP Directive]]. In September 2008 at a hearing of the European Parliament's Urban Lodgment Intergroup, Energy Commissioner Andris Piebalgs is quoted as saying, “security of supply really starts with energy efficiency.”<ref>{{cite web |url =http://www.cogeneurope.eu/Downloadables/Publications/230908_Energy_Efficiency_Industrial_Forum_Security_of_Supply.pdf |title =Energy Efficiency Industrial Forum Position Paper: energy efficiency – a vital component of energy security }}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Energy efficiency and cogeneration are recognized in the opening paragraphs of the European Union's Cogeneration Directive 2004/08/EC. This directive intends to support cogeneration and establish a method for calculating cogeneration abilities per country. The development of cogeneration has been very uneven over the years and has been dominated throughout the last decades by national circumstances.

The European Union generates 11% of its electricity using cogeneration.<ref>{{cite web|url=http://www.cogeneurope.eu/medialibrary/2011/04/21/2bc24419/240311%20COGEN%20Europe%20press%20release.pdf|title=2011 - Cogen -Experts discuss the central role cogeneration has to play in shaping EU energy policy|website=cogeneurope.eu|accessdate=28 April 2018|url-status=live|archiveurl=https://web.archive.org/web/20170620044706/http://www.cogeneurope.eu/medialibrary/2011/04/21/2bc24419/240311%20COGEN%20Europe%20press%20release.pdf|archivedate=20 June 2017}}</ref> However, there is large difference between Member States with variations of the energy savings between 2% and 60%. Europe has the three countries with the world's most intensive cogeneration economies: Denmark, the Netherlands and Finland.<ref>{{cite web |url=http://www.cogeneurope.eu/Downloadables/Publications/Cogeneration_Europe_Draft_paper_on_Security_of_Supply_in_EU_energy_policy.pdf |title=COGEN Europe: Cogeneration in the European Union's Energy Supply Security }}{{dead link|date=August 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Of the 28.46 TWh of electrical power generated by conventional thermal power plants in Finland in 2012, 81.80% was cogeneration.<ref>{{cite web |url=http://energia.fi/tilastot-ja-julkaisut/sahkotilastot/sahkontuotanto/sahkon-hankinta-energialahteittain |title=Electricity Generation by Energy Source |url-status=dead |archiveurl=https://web.archive.org/web/20140220125742/http://energia.fi/tilastot-ja-julkaisut/sahkotilastot/sahkontuotanto/sahkon-hankinta-energialahteittain |archivedate=2014-02-20 }}</ref>

Other European countries are also making great efforts to increase efficiency. Germany reported that at present, over 50% of the country's total electricity demand could be provided through cogeneration. So far, Germany has set the target to double its electricity cogeneration from 12.5% of the country's electricity to 25% of the country's electricity by 2020 and has passed supporting legislation accordingly.<ref>{{cite web|title=KWKG 2002|url=http://www.gesetze-im-internet.de/kwkg_2002/__1.html|url-status=dead|archiveurl=https://web.archive.org/web/20140202095900/http://www.gesetze-im-internet.de/kwkg_2002/__1.html|archivedate=2014-02-02}}</ref> The UK is also actively supporting combined heat and power. In light of UK's goal to achieve a 60% reduction in carbon dioxide emissions by 2050, the government has set the target to source at least 15% of its government electricity use from CHP by 2010.<ref>{{cite web |url=http://www.defra.gov.uk/environment/climatechange/uk/energy/chp/index.htm |title=DEFRA Action in the UK - Combined Heat and Power |url-status=dead |archiveurl=https://web.archive.org/web/20100612100647/http://www.defra.gov.uk/environment/climatechange/uk/energy/chp/index.htm |archivedate=2010-06-12 }}</ref> Other UK measures to encourage CHP growth are financial incentives, grant support, a greater regulatory framework, and government leadership and partnership.

According to the IEA 2008 modeling of cogeneration expansion for the G8 countries, the expansion of cogeneration in France, Germany, Italy and the UK alone would effectively double the existing primary fuel savings by 2030. This would increase Europe's savings from today's 155.69 Twh to 465 Twh in 2030. It would also result in a 16% to 29% increase in each country's total cogenerated electricity by 2030.

Governments are being assisted in their CHP endeavors by organizations like [[COGEN Europe]] who serve as an information hub for the most recent updates within Europe's energy policy. COGEN is Europe's umbrella organization representing the interests of the cogeneration industry.

The European [[public–private partnership]] [[Fuel Cells and Hydrogen Joint Technology Initiative|Fuel Cells and Hydrogen Joint Undertaking]] [[Framework Programmes for Research and Technological Development|Seventh Framework Programme]] project ene.field deploys in 2017<ref>{{cite web|url=http://www.fch-ju.eu/sites/default/files/documents/sga2012/Presentation%20Fiona%20Riddoch-%20Session%20II.pdf|title=5th stakeholders general assembly of the FCH JU|website=fch-ju.eu|accessdate=28 April 2018|url-status=live|archiveurl=https://web.archive.org/web/20131110030750/http://www.fch-ju.eu/sites/default/files/documents/sga2012/Presentation%20Fiona%20Riddoch-%20Session%20II.pdf|archivedate=10 November 2013}}</ref> up 1,000 residential fuel cell Combined Heat and Power ([[micro-CHP]]) installations in 12 states. Per 2012 the first 2 installations have taken place.<ref>{{cite web|url=http://enefield.eu/|title=ene.field|accessdate=15 May 2015|url-status=live|archiveurl=https://web.archive.org/web/20161002024915/http://enefield.eu/|archivedate=2 October 2016}}</ref><ref>[http://www.h2fc-fair.com/hm13/images/ppt/10we/1420-1.pdf European-wide field trials for residential fuel cell micro-CHP] {{webarchive|url=https://web.archive.org/web/20161109221035/http://www.h2fc-fair.com/hm13/images/ppt/10we/1420-1.pdf |date=2016-11-09 }}</ref><ref>[http://enefield.eu/wp-content/uploads/2013/04/Progress-Report-1-M1-M6-Final.pdf ene.field Grant No 303462] {{webarchive |url=https://web.archive.org/web/20131110070103/http://enefield.eu/wp-content/uploads/2013/04/Progress-Report-1-M1-M6-Final.pdf |date=November 10, 2013 }}</ref>

===Cogeneration in the United Kingdom===
In the [[United Kingdom]], the ''Combined Heat and Power Quality Assurance'' scheme regulates the combined production of heat and power. It was introduced in 1996. It defines, through calculation of inputs and outputs, "Good Quality CHP" in terms of the achievement of primary energy savings against conventional separate generation of heat and electricity. Compliance with Combined Heat and Power Quality Assurance is required for cogeneration installations to be eligible for government subsidies and tax incentives.<ref>{{cite web|url=http://chpqa.decc.gov.uk|title=Combined Heat and Power Quality Assurance Programme|website=decc.gov.uk|accessdate=28 April 2018|url-status=live|archiveurl=https://web.archive.org/web/20141030232902/http://chpqa.decc.gov.uk/|archivedate=30 October 2014}}</ref>

===Cogeneration in the United States===
[[File:Mirant Kendall Cogeneration Station.jpg|thumb|right|The 250 [[megawatt|MW]] [[Kendall Cogeneration Station]] plant in [[Cambridge, Massachusetts]]]]

Perhaps the first modern use of [[energy recycling]] was done by [[Thomas Edison]]. His 1882 [[Pearl Street Station]], the world's first commercial power plant, was a combined heat and power plant, producing both electricity and thermal energy while using waste heat to warm neighboring buildings.<ref>{{cite web|url=http://www.cogeneration.net/ThomasEdisonsCogenPlant.htm|title=World's First Commercial Power Plant Was a Cogeneration Plant|url-status=dead|archiveurl=https://web.archive.org/web/20080425015724/http://www.cogeneration.net/ThomasEdisonsCogenPlant.htm|archivedate=2008-04-25|access-date=2008-06-15}}</ref> Recycling allowed Edison's plant to achieve approximately 50 percent efficiency.

By the early 1900s, regulations emerged to promote rural electrification through the construction of centralized plants managed by regional utilities. These regulations not only promoted electrification throughout the countryside, but they also discouraged decentralized power generation, such as cogeneration.

By 1978, Congress recognized that efficiency at central power plants had stagnated and sought to encourage improved efficiency with the [[Public Utility Regulatory Policies Act]] (PURPA), which encouraged utilities to buy power from other energy producers.

Cogeneration plants proliferated, soon producing about 8% of all energy in the United States.<ref name=localpower>{{cite web|url=http://www.localpower.org/documents/report_worldsurvey06.pdf|title=World Survey of Decentralized Energy|date=May 2006}}</ref> However, the bill left implementation and enforcement up to individual states, resulting in little or nothing being done in many parts of the country.{{citation needed|date=December 2012}}

The [[United States Department of Energy]] has an aggressive goal of having CHP constitute
20% of generation capacity by the year 2030. Eight Clean Energy Application Centers<ref>[http://www.gulfcoastcleanenergy.org/WhatisCHP/StateInformation/OtherStates/tabid/1349/Default.aspx Eight Clean Energy Application Centers] {{webarchive|url=https://archive.is/20130415062907/http://www.gulfcoastcleanenergy.org/WhatisCHP/StateInformation/OtherStates/tabid/1349/Default.aspx |date=2013-04-15 }}</ref> have been established across the nation whose mission is to develop the required technology application knowledge and educational infrastructure necessary to lead "clean energy" (combined heat and power, waste heat recovery and district energy) technologies as viable energy options and reduce any perceived risks associated with their implementation. The focus of the Application Centers is to provide an outreach and technology deployment program for end users, policy makers, utilities, and industry stakeholders.

High electric rates in New England and the Middle Atlantic make these areas of the United States the most beneficial for cogeneration.<ref name=electricitydata>{{cite web|url=http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a|title=Electricity Data|url-status=live|archiveurl=https://web.archive.org/web/20150531215733/http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a|archivedate=2015-05-31}}</ref><ref name=energysaving>{{cite web|url=http://newenglandcondo.com/articles/773/1/Energy-Saving-Incentives/Page1.html|title=New England Energy|url-status=live|archiveurl=https://web.archive.org/web/20150123213042/http://newenglandcondo.com/articles/773/1/Energy-Saving-Incentives/Page1.html|archivedate=2015-01-23}}</ref>

==Applications in power generation systems==

===Non-renewable===
Any of the following conventional power plants may be converted to a combined cooling, heat and power system:<ref>{{cite book|last=Masters|first=Gilbert|title=Renewable and efficient electric power systems|year=2004|publisher=Wiley-IEEE Press|location=New York}}</ref>
*[[Coal]]
*[[Gas turbine#Microturbines|Microturbine]]
*[[Natural gas]]
*[[Nuclear power]]
*[[Oil]]
*[[Gas turbine|Small gas turbine]]

===Renewable===
*[[Solar thermal energy|Solar thermal]]
*[[Biomass heating system#Combined heat and power|Biomass]]
*[[Hydrogen]] [[fuel cell]]
*Any type of [[Gas compressor|compressor]] or [[turboexpander]], such as in [[compressed air energy storage]]
*[[Geothermal]]

==See also==
{{Portal|Energy|Renewable energy}}
{{Div col}}
*[[Air separation]]
*[[Carnot cycle]]
*[[Carnot method]]
*[[CHP Directive]]
*[[Cost of electricity by source]]
*[[Distributed generation]] (more general term encompassing CHP)
*[[District heating]]
*[[Electricity generation]]
*[[Electrification]]
*[[Energy policy of the European Union]]
*[[Environmental impact of electricity generation]]
*[[European Biomass Association]]
*[[Industrial gas]]
*[[Micro combined heat and power]]
*[[New York City steam system]]
*[[Rankine cycle]]
*[[Absorption refrigerator]]
*[[Boiler]]
{{Div col end}}

==Further reading==
* {{cite book |title=Steam, Its Generation and Use |url=https://books.google.com/books?id=nqMMAAAAYAAJ |edition=35 |year=1913 |publisher=Babcock & Wilson Company}} <!-- An engineering handbook widely used by those involved with various types of boilers. Contains numerous illustrations, graphs and useful formulas. (Not specific to cogeneration). ''The link leads to an entire free e-Book of an early edition. For current practice a more modern edition is recommended.'' -->

==References==
{{Reflist|30em}}

{{Electricity generation}}

[[Category:Cogeneration| ]]
[[Category:Heating, ventilating, and air conditioning]]
[[Category:Energy conversion]]
[[Category:Sustainable technologies]]
[[Category:Renewable energy]]