The joint production of useful heat and electricity.
For example, furnaces may be replaced with gas turbogenerators that produce electricity while the host exhaust still serves as a heat source.
An important avenue of conservation, it effectively avoids the waste of heat that normally occurs at centralized power plants.
Combined heat and power: The recovery of heat (a waste product of electrical generation) which is then put back to use for heating, cooling, or more electrical generation (e.g. the waste heat from a gas turbine used to create steam, which can power another turbine). Useful for increased efficiency of onsite power generation.
In the Middle Ages, excess heat from cooking fires was captured to turn roasting spits, and Edison's Pearl Street station piped steam to Drexel Morgan to warm the offices of his potential investors....While a conventional gas turbine squanders two thirds of its energy input into the atmosphere, cogeneration can result in a total energy efficiency of 70 percent or higher, and cuts CO2 emissions in half.
--Steve Silberman, "The Energy Web," Wired, 9.07, p. 119

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