Capacity Factor Across Sources
A side-by-side of typical, public capacity factors shows why firm clean sources anchor a reliable low-carbon grid.
Comparing typical capacity factors across sources makes the firm-versus-variable divide concrete. The numbers below are public, widely reported typical ranges; real values vary by site, vintage, and region. They are not performance claims for any specific plant, and the fusion entry is a design objective rather than a measured value.
The comparison
Firm thermal sources cluster high because they run continuously by design. Variable renewables cluster lower because their fuel — sun and wind — is intermittent. This does not make renewables inferior; it means their value is in energy volume and abundant output, while firm sources provide the reliability backbone. A clean grid uses both.
Reading the chart
A high capacity factor means more energy per unit of installed capacity and, usually, greater firmness. But two firm sources with the same capacity factor can differ in emissions: gas is firm yet emits CO₂, while fission and fusion are firm and low-carbon. The goal of the clean transition is to fill the high-capacity-factor rows with low-carbon options.
- Firm sources (geothermal, fission, gas) sit high; variable renewables sit lower.
- Capacity factor is about quantity and firmness, not carbon.
- Gas is firm but emits; fission and fusion aim to be firm and clean.
- Fusion's entry is a design goal; treat it as such.
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.
The honest takeaway: decarbonization means moving firm capacity from the carbon-emitting rows to the clean ones — the role fusion is being designed for.