concepts
Capacity factor
Definition. The share of the year a power plant actually produces electricity at its full nameplate output. A 1 GW plant running at 50% capacity factor over a year delivers 0.5 GW × 8,760 hours = 4,380 GWh.
Typical values
| Generation type | Capacity factor | Why |
|---|---|---|
| Nuclear | 90-95% | Designed for baseload; only goes offline for refueling outages (~30 days every 18-24 months) and planned maintenance. CEG's fleet averages 94-95%. |
| Geothermal | 75-95% | Heat source is always available; limited by reservoir management and plant maintenance. |
| Combined-cycle gas baseload | 50-65% | Economic dispatch — runs when spark spread is positive. |
| Combined-cycle gas peaker | 5-20% | Designed to run only during high-demand hours. |
| Hydro | 30-50% | Limited by seasonal water availability and reservoir management. |
| Wind (offshore) | 40-55% | Steadier wind. |
| Wind (onshore) | 30-40% | Variable wind. |
| Solar | 20-28% | Daylight only, plus weather. |
| Battery storage | n/a (different metric) | Sized by duration (4hr, 8hr) and cycles. |
Why it matters for the AI thesis
AI data centers run 24/7. A 1 GW data center load is power demand for 8,760 GWh/year, constantly. To match that with solar (25% CF) requires 4 GW of nameplate solar plus enough storage to bridge nights and cloudy days — economically uncompetitive with firm dispatchable sources. The hyperscalers buying nuclear PPAs (Microsoft–CEG, Meta–CEG, Amazon–TLN) are buying capacity factor as much as they're buying clean attributes.
This is the structural reason behind the ai power bottleneck thesis. The set of zero-carbon, dispatchable, high-capacity-factor assets in the US is fixed: existing nuclear and existing hydro. Geothermal is small. Everything else either has low CF (wind/solar) or carbon (gas).
Where you encounter this in filings
Utility 10-K Item 1 (Business) generally discloses fleet-wide capacity factor. Look for "fleet-wide net capacity factor" in MD&A or operations sections. CEG's 10-K reports 94-95% on the nuclear fleet (FY2025).
Common misconceptions
- "Nameplate capacity" (the 1 GW number) is the peak, not the average. People conflate them and overstate solar/wind delivered output.
- High capacity factor ≠ low cost. Nuclear has high CF and high capex; gas peakers have low CF and low capex per delivered MWh in their use case. Different roles.
- A higher CF can sometimes be a sign of stress, not efficiency — if every plant in a region is running at >90% CF, the system has no reserve margin.
Related
- power purchase agreement — how CF interacts with PPA pricing
- pjm capacity market — payment for capacity availability, separate from energy
- utilities power — sector overview