LEARN / GLOSSARY
Capacity factor
Electricity actually produced over a period, divided by the maximum possible at continuous full power. The denominator is usually net summer capacity rather than nameplate, and the difference is rarely stated.
Definition
Capacity factor is the electricity a generator actually produced over a period relative to the maximum it could have produced running continuously at full power. The result is a ratio, usually expressed as a percentage, describing how a specific unit was operated rather than the condition of the system around it.
Measurement noteEIA calculates capacity factor using net generation divided by net summer capacity, not by nameplate capacity. A capacity factor quoted against nameplate and one quoted against net summer capacity are different numbers for the same plant, and published figures rarely state which basis was used.
Why the dictionary version is insufficient
A capacity factor is often read as a measure of quality, with a higher number indicating a better plant. The number describes how a unit was operated and what constrained it. A peaking plant with a low capacity factor is doing the job it was built for, and a plant idled by transmission constraints records the same low number for an entirely different reason.
Why it matters for capacity
Capacity factor is what converts a nameplate figure into expected energy, so it is the term that makes announcements comparable. Without it, two projects with identical nameplate ratings and different operating profiles appear equivalent on paper and deliver very different quantities of electricity.
Related terms
Nameplate capacity · Firm power · Capacity utilization
Appears in
Why Reindustrialization Requires More Electricity
Read next
Why Reindustrialization Requires More Electricity
Sources
- U.S. Energy Information Administration, Electricity generation, capacity, and sales in the United States. eia.gov