What this data measures

The capacity factor of electricity generators by fuel source and state — the ratio of actual generation to the maximum possible generation if the plant ran at full nameplate capacity the entire year. Higher capacity factors indicate more intensive utilization.

How this data is constructed

Capacity factors are computed from EIA data: actual net generation by source and state comes from Form EIA-923; nameplate generating capacity by source and state comes from Form EIA-860. The capacity factor for each source is computed as actual generation divided by (nameplate capacity × the number of hours in that year — 8,784 in a leap year, 8,760 otherwise). Because nameplate capacity is measured at year end while generation covers the whole year, a source can exceed 100% in a state where a plant ran for most of the year and then retired, or was uprated mid-year: the electricity it produced is divided by a capacity smaller than the one that produced it. These values are shown as reported. Note also that using nameplate rather than net summer capacity puts these figures several points below the capacity factors EIA publishes.