Field Notes · Common mistakes
One 1,000 kW genset: 590 kW at 45°C
Gas engines and turbines lose output in heat. Why plants in hot climates must be sized on the site-rated curve, not the ISO rating.
The plant you paid for is not always the plant you get in July. The ISO rating is on the front page of the datasheet; the derate table sits further back.
What the datasheets say
- One maker's 1,000 kW natural-gas genset datasheet (Cummins C1000N6C, 2017) lists a derate factor of 0.75 at 40°C and 0.59 at 45°C, at sea level. At 45°C that genset makes about 590 kW.
- Gas turbines are affected too: an aeroderivative turbine's output falls by nearly 26% at 45°C compared with ISO conditions, with efficiency down by more than 11% in relative terms (Wärtsilä, an engine maker).
Why it hurts
Peak heat often brings peak load, especially where cooling drives demand. A plant sized at ISO rating comes up short at exactly the wrong hour, and the operator sheds load, burns diesel, or flares the gas it meant to use.
The fix
Size on the site-rated curve at the design-day maximum temperature, altitude and fuel methane number, then check it against the hottest hour of the load profile. Read the derate table for the specific equipment, not the brochure figure.
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