A Proposed Definition of CHP Efficiency

08 June 2010

Many alternative approaches for determining a useful definition of combined heat and power fossil power plant efficiency have been proposed, although most fail to produce a universal definition. This article shows how an exergy analysis supplies the elusive solution.


Combined heat and power (CHP), also known as cogeneration, describes fossil-fired power plants that generate multiple product streams, usually thermal energy and electricity. In most cases, the thermal energy product comprises one or more streams of steam at different pressures and temperatures that are used by an end-use customer for district heating and/or cooling, manufacturing process needs, or similar industrial and/or residential uses.

The key benefit of CHP is the attractive economics produced by generating electricity and useful thermal energy from a single fuel source. A quick and easy assessment of the benefits of CHP can be found in “CHP: Helping to Promote Sustainable Energy” (POWER, June 2009).

Although there is no question about the benefit of CHP’s effectiveness in fuel utilization and reduced emissions, what has been missing so far is a standardized and consistent definition of CHP efficiency that would enable industry participants to measure and rank a wide variety of cogeneration plants on a thermodynamically consistent basis. 

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A Proposed Definition of CHP Efficiency

POWER Magazine
June 2010