Field Notes · Common mistakes
Most of your fuel leaves as heat
A gas engine turns roughly 28 to just over 40% of its fuel into electricity. Recovering the heat lifts total efficiency to about 80%.
Gas-engine projects are usually scoped, and paid, in megawatts of electricity. The heat has no owner and no tariff, so it is often treated as waste.
Where the energy goes
- On electricity alone, a reciprocating engine converts roughly 28% to just over 40% of its fuel (HHV basis).
- The rest leaves as heat, and the exhaust is roughly half of the heat that can be recovered (US DOE, CHP Technologies: Reciprocating Engines, 2023).
- With heat recovery, total efficiency reaches about 80%. Separate power and heat systems typically manage about 50% (US EPA).
Skipping heat recovery means paying for heat twice: once in the engine's fuel, where it is thrown away, and again in fuel for a boiler or chiller. That is more fuel and more CO2.
The fix
Before freezing the layout, list every heat sink within reach: process heat, crude heating, absorption chilling for hot climates, desalination pre-heat. If there is no heat buyer yet, leave the space and tie-ins so heat recovery can come in a second phase.
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