Capacity Factor Drivers

U.S. nuclear plants run at 93% capacity factor. Wind farms average 35%. Solar sits around 25%. These gaps are not random. Four distinct forces determine how much of a generator's theoretical maximum output it actually delivers.

Capacity factor is driven by four things. First, resource availability: the sun sets, the wind dies, and rivers dry up. Solar and wind capacity factors are capped by nature. Second, dispatch economics: even if a gas plant could run 24/7, grid operators may not call on it because cheaper generators are available. Gas peakers run at 10-15% capacity factor not because they break, but because they're expensive to operate. Third, maintenance: planned outages for refueling, inspections, and overhauls take plants offline for weeks. Nuclear refueling outages last 20-30 days every 18-24 months. Fourth, forced outages: equipment failures, fuel supply disruptions, or extreme weather force unplanned shutdowns.

Decompose a nuclear plant's 93%. Available 365 days minus ~25 days of refueling = 340 operating days. Forced outage rate of ~2%. Effective capacity factor: roughly (340/365) x 0.98 = 91%. The remaining 2% comes from power uprates and favorable conditions.

Decompose a wind farm's 35%. Wind blows at usable speeds roughly 70-80% of hours, but at varying intensity. Average output is about 35% of rated capacity.

Why would a gas peaker's capacity factor drop from 15% to 5% as more solar is built on the same grid?

Dispatch economics shift. Midday solar displaces gas generation during peak hours, reducing the number of hours the peaker is called to run. The turbine is not broken; it is simply not needed as often.

Understanding what drives capacity factor separates equipment capability from economic and physical reality.

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