Every CHP application involves the recovery of heat that would otherwise be wasted. In this way, CHP increases fuel-use efficiency.
Two measures are commonly used to quantify the efficiency of a CHP system:
total system efficiency and effective electric efficiency.
- Total system efficiency is the measure used to compare the efficiency of a CHP system to that of conventional supplies (the combination of grid-supplied electricity and useful thermal energy produced in a conventional on-site boiler). If the objective is to compare CHP system energy efficiency to the efficiency of a site's conventional supplies, then the total system efficiency measure is likely the right choice.
- Effective electric efficiency is the measure used to compare CHP-generated electricity to electricity generated by power plants. If CHP electrical efficiency is needed to compare CHP to conventional electricity production (i.e., grid-supplied electricity), then the effective electric efficiency metric is likely the right choice.
Certain assumptions are implicit in each methodology that are not appropriate in all cases. Consequently, the measure employed should be selected carefully and the results interpreted with caution.
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