What is capacity factor?
Why a 1 GW nuclear plant makes far more power than a 1 GW solar farm.
Capacity is what a plant could produce at full tilt; capacity factor is how much it actually produces over a year, as a percentage of that maximum. A nuclear plant might run at 90%+, so it's almost always on. A solar farm, limited by night and weather, might average 15–25%. Onshore wind lands around 35%. So nameplate capacity alone is misleading: a gigawatt of nuclear generates several times the annual energy of a gigawatt of solar.
This is why comparing grids and fuels by capacity tells only part of the story, and why nrgmap is careful to label capacity as capacity, not generation. It's also why the energy transition needs more nameplate gigawatts of wind and solar than the fossil capacity they replace. To deliver the same energy, you build more of a lower-capacity-factor resource and pair it with storage.
Frequently asked questions
What is capacity factor?
The ratio of a plant's actual annual output to what it would produce running flat-out all year. Nuclear is ~90%, wind ~35%, solar ~15–25%.
Why does capacity factor matter?
Because two plants with the same capacity can produce very different amounts of energy. It's why a gigawatt of solar and a gigawatt of nuclear are not equivalent.