Capacity factor is the ratio of the electricity produced by an electricity generation facility in a certain period to the maximum electricity it could produce if it operated uninterruptedly with full installed power in the same period. It helps understand not only how large the plant is, but also the extent to which it uses its current capacity over time.
How is it calculated?
The simplified formula is:
Capacity factor = Actual electricity production / Maximum theoretical electricity production
The maximum theoretical production is calculated by multiplying the installed power of the power plant by the number of hours in the examined period. For example, a power plant does not operate at full power every hour due to maintenance, refueling, malfunction, low demand or unavailability of energy source.
Are installed capacity and production the same thing?
No. Installed power refers to the instantaneous power capacity that a facility can provide under certain conditions. Electricity production is the amount of energy generated as a result of using this power over time.
Two facilities with the same installed capacity may produce different amounts of electricity at the end of the year. The capacity factor makes part of this difference visible.
What affects the capacity factor?
- Planned maintenance and refueling
- Unplanned downtimes and equipment reliability
- Availability of primary resource such as wind, sun or water
- Electricity demand and market conditions
- Network restrictions
- fuel supply
- The way the power plant follows load or provides reserves
Therefore, a low or high capacity factor alone does not indicate whether the facility is "good" or "bad".
Can different technologies be directly compared?
Comparison can be made, but the result should be interpreted with caution. Solar and wind production depends on weather conditions. Nuclear and some thermal power plants can provide production for long periods of time except for planned maintenance. Hydroelectric production may be affected by water conditions and reservoir management.
The electricity system's need is not just the total annual production. The hours at which production takes place, its predictability, flexibility, transmission need and system cost are also important.
Which question does the capacity factor not answer?
This metric alone does not indicate cost, carbon emissions, safety, environmental impact or network value. Capacity factor when evaluating energy technologies; should be read together with indicators of cost, emissions, reliability and flexibility.
Resources
- IAEA, Power Reactor Information System: https://pris-stats.iaea.org/
- IEA, Nuclear Power: https://www.iea.org/energy-system/renewables-and-low-emissions/nuclear