Capacity Factor

Capacity factor is a useful concept in planning and analysing energy production in human power systems. It is computed for a given power production facility as

${\text{capacity factor}}={\frac {\text{average actual power output}}{\text{nameplate output}}}$

The nameplate output is the rated (usually maximum) output of the facility. However, any given facility may produce power at a reduced rate at some times for various reasons, and/or might be shut down during other times for maintenance or other reasons. Hence, the actual power output averaged over a sufficiently long time is nearly always less than the nameplate output.

Reasons for Capacity Factors Less Than One

The facility could be shut down for periods of time due to:

• Planned maintenance
• Unplanned maintenance
• Accidents
• Labour relations/conflicts
• Lack of availability of feedstock (coal, biomass, etc.)
• Planned shutdown due to low power demand
• Shutdown because of cheaper power being available from another source
• Natural disasters

The facility could produce power at a rate less than its nameplate capacity for many periods of time. This could be due to:

• Deliberately running at less than full capacity due to low demand for power
• Reduced availability of the primary energy source, especially for solar and wind power
• Technical failures such as overheating, minor equipment malfunctions, etc.
• Insufficient labour

Typical Capacity Factors

Nuclear power plants have among the highest capacity factors. They are usually only shut down for maintenance and refueling. In fact some nuclear reactors operate at above their nameplate capacity for long periods of time which can lead to capacity factors greater than 1. Currently the highest capacity factor for a nuclear plant in the world is the Balakovo 2 reactor in Russia with a capacity factor of 1.066.

For calculating wind power capacity factors one needs wind speed probability distributions. One possible place to find them is the Global Wind Atlas maintained by the Technical University of Denmark.

According to a case study that took place in the SouthWest United States, It was noted that concentrated power plants have a high capacity value of 79% to 92% when the storage of thermal energy is involved. without the thermal energy storage plan, the working capacity value would decrease to between 60% to 86% which would be considered a decent capacity factor..

Questions for students to answer if they want: What is a more typical capacity factor for nuclear plants? (e.g. find a world average, or the U.S. average, and give a citation). What are typical capacity factors for wind farms? (...citation) What are typical capacity factors for Solar PV and/or for CSP facilities? (...citation). What are typical capacity factors for hydro power plant? (...citation)