What is Cogeneration?
'''Cogeneration''' (also '''combined heat and power''', '''CHP''') is the use of a [[heat engine]] or a [[power station]] to make both [[electricity]] and useful [[heat]] at the same time. Conventional power plants [[Emission|emit]] the heat created as a byproduct of [[electricity generation]] into the environment through [[cooling tower]]s, as [[flue gas]], or by other means. Combined heat and power captures the [[waste heat]] for domestic or industrial [[heating]] purposes, either very close to the plant, or - especially in [[Scandinavia]] and eastern [[Europe]] - for distribution through pipes to [[district heating|heat local housing]]. Cogeneration is a [[thermodynamics|thermodynamically]] [[Energy efficiency|efficient]] use of [[fuel]]. Byproduct heat at moderate temperatures (100 to 180[[°C]]) can also be used in [[Gas-absorption refrigerator|absorption chillers]] for cooling. A plant producing electricity, heat and cold is sometimes called '''[[regeneration]]''' or more generally: '''polygene ration''' plant. [[File:Masnedø power station.jpg|300px|thumb|right|[[Masnedø]] ''CHP'' power station in [[Denmark]]. This station burns straw as fuel. The plant heats adjacent greenhouses.]] Thermal power plants (including those that use [[uranium|fissile elements]] or burn [[coal]], [[petroleum]], or [[natural gas]]), and [[heat engine]]s in general, do not convert all of their available energy into electricity. In most heat engines, a bit more than half is wasted as excess heat (see: [[Second law of thermodynamics]]). By capturing the excess heat, CHP uses heat that would be wasted in a conventional [[power plant]], potentially reaching an [[Energy efficiency|efficiency]] of up to 70%, compared with at most 40% for the conventional plants. Less fuel needs to be consumed to produce the same amount of useful energy. Less pollution is produced for a given economic benefit. An exact match between the heat and electricity needs rarely exists. A CHP plant can either meet the need for heat (''heat driven operation