Work out thermal efficiency instantly with clear inputs, formula shown and shareable results.
Thermal efficiency is net work divided by heat supplied. 350 kJ of work from 1000 kJ of heat is 35% efficient, rejecting 650 kJ. Power engineers often quote the reciprocal as heat rate: 35% corresponds to 10,286 kJ per kWh, and the theoretical floor is 3600 kJ/kWh at 100% efficiency.
Thermal efficiency
efficiency = W(net) / Q(in)
Heat rate
heat rate = 3600 / efficiency in kJ/kWh
About 35-40% for a coal steam plant, 40% for a large diesel, and up to 62% for a combined cycle gas turbine.
Because fuel is bought by energy content. Heat rate reads directly as fuel consumed per unit of electricity sold.