Contrasting CHP with Separate Heat and Power:
An Efficiency and Emissions Comparison
CHP improves energy efficiency by capturing heat that is normally discarded by centralized electric power plants. Reduced transmission losses further boost the efficiency of onsite CHP installations.
Roughly two-thirds of the energy contained in fuel is lost as heat in typical electric generating plants. Even state-of-the-art gas turbine generators capture less that half of the energy content of fuel as electricity.
CHP results in more useful energy per pound, Btu, or dollar of fuel and less pollution per unit of energy used. This can benefit facilities' balance sheets and air quality simultaneously.
The figures below illustrate how a facility's decision to apply CHP can enhance efficiency and reduce net air pollution compared to the conventional scenario of operating an onsite boiler for heat while buying electricity from the grid. The CHP scenario achieves 75% energy efficiency compared to 49% with the conventional separate heat and power approach (top figure). By displacing centrally generated electricity, the CHP-using facility meets its energy needs with only 38% of smog-forming nitrogen oxides (NOx) emissions than would be conventionally released (17 tons versus 45 tons per year--bottom figure).
Note that the figures are for illustration. CHP performance relative to separate heat and power depends on numerous site- and project-specific factors. (Figures provided courtesy of Joel Bluestein, Energy and Environmental Analysis, Inc., Arlington, VA.)
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