Capacity Factor Explained

Capacity factor is the fraction of nameplate power a source actually delivers over time; it separates firm sources from variable ones.

Capacity factor is the ratio of the energy a plant actually produces over a period to the energy it would produce running at full nameplate power the whole time. A 100 MW plant that averages 90 MW has a 90% capacity factor. It is one of the clearest single numbers for comparing how much real energy a source delivers per unit of installed capacity.

What drives it

Variable sources have capacity factors set largely by nature: solar by daylight and weather, wind by the wind resource. Firm thermal sources have capacity factors set by design and maintenance: how often they run and how much downtime they take. High capacity factor is one component of firmness, but not the whole story — timing matters too, since energy delivered at the wrong hour has limited value.

Capacity factor and fusion — honestly

Fusion is designed for high capacity factor as a firm source, but this is a target, not a measured result: the machines are design-and-simulation studies. For the burner, availability is an open engineering gate (analyzed at roughly 0.86 to 0.995 in simulation), which is short of hyperscale Tier III standards — an honest limit, not an economic claim. Capacity factor should be read as a design objective for fusion, not an achievement.

• Capacity factor = actual energy / theoretical maximum at full power.
• Variable sources: set by nature; firm sources: set by design and uptime.
• High capacity factor supports firmness but timing also matters.
• For fusion it is a design goal; availability remains an open gate.

Design-and-simulation framing. The Kronos machines are today design and simulation studies: the breeder (Hyperion) and the burner (Aegis / MetroVolt). No hardware net-gain has been demonstrated. Breeder construction is planned to begin Q2 2027, with first-of-a-kind (FOAK) first tritium targeted around 2030. Comparisons on this page are qualitative and use only public, defensible figures; nothing here is a performance guarantee.

When comparing sources, capacity factor explains why a small amount of firm capacity can be worth a large amount of variable capacity for reliability.