What Is a Capacity Factor?

Capacity factor is the honest yardstick of a power plant's output. A 100 MW solar farm running at a 25% capacity factor produces the same annual energy as a 25 MW plant running flat out. The gap between nameplate capacity and capacity factor explains why comparing technologies by installed megawatts alone misleads: a gigawatt of nuclear (90%+ capacity factor) generates far more electricity than a gigawatt of solar.

For solar, capacity factor depends chiefly on the local resource and hardware: the sunniest Southwest sites with single-axis trackers reach around 30%, while the Northeast runs closer to 17-20%. Wind varies with siting even more. Capacity factors also decline modestly with equipment age and curtailment — when grid congestion forces plants to reduce output below what the resource would support.