How is the capacity factor of a power plant defined?

• A. The maximum possible energy output divided by actual energy output
• B. The installed capacity divided by site area
• C. Actual energy output divided by the maximum possible energy output
• D. The average annual energy production

Answer: (C)

Capacity factor measures how much energy a plant actually produces compared with what it could produce if it ran at full power for the entire time period you’re looking at. It’s the ratio of actual energy output to the maximum possible energy output, where the maximum is the plant’s installed capacity multiplied by the time period (in hours). This makes the capacity factor a dimensionless number (often expressed as a percentage) that shows how fully the plant’s potential is being used.

For example, a 500 MW plant over a year could theoretically produce 500 MW × 8760 hours ≈ 4.38 million MWh if it ran at full capacity all year. If it actually produced 2.0 million MWh, its capacity factor would be about 2.0 / 4.38 ≈ 0.46, or 46%. This reflects both downtime and any operating limitations.

The other options don’t fit because they either invert the ratio, relate capacity to land area, or refer to total energy without comparing it to what could have been produced.