An undersized generator becomes overloaded and its engine life drops sharply; an oversized generator running at low load operates at very poor efficiency with high fuel consumption — a phenomenon known as "light-load operation" or wet stacking.

Altitude Correction

Per ISO 3046, for every 100 m of elevation above 1000 m, diesel engine power drops by roughly 1%. Turbocharged engines largely compensate for this loss.

Efficiency at Partial Loads

Diesel engines reach peak efficiency at 70–80% of rated load. Below 30% load, fuel consumption per kWh rises sharply and carbon (wet stacking) builds up; in that case either choose a smaller generator or run two units in parallel.