Capacity factor

Capacity factor is the ratio of a power plant's actual energy output over a period to the maximum energy it could have produced if it ran at full rated capacity for that entire period. It is calculated as actual energy output / (rated capacity × time period), usually expressed as a percentage over a month or year.

Capacity factor varies enormously by generation type and is one of the clearest ways to compare how reliably different technologies deliver power. Dispatchable sources like nuclear or combined-cycle gas plants can run near continuously and post high capacity factors, while intermittent renewables such as solar and wind are inherently limited by weather and daylight, giving them structurally lower capacity factors even when the underlying technology performs exactly as designed. This is why comparing capacity factor across technologies without adjusting for that structural difference is a common misreading — a lower capacity factor doesn't necessarily mean worse performance.

The metric matters for planning generation mix, evaluating a plant's economics, and estimating how much installed capacity is needed to reliably meet forecast demand from load forecasting. Grid operators use it alongside grid analytics to plan for the variability that low-capacity-factor renewable sources introduce, and utilities increasingly draw on granular advanced metering infrastructure data to better understand how demand aligns with when variable generation is actually available.