What is capacity factor and how does it affect the electricity supply from a wind farm?

• A. Capacity factor = actual energy output / maximum possible energy output; wind variability lowers the factor and influences reliability and planning
• B. Capacity factor equals the installed capacity of the wind farm
• C. Capacity factor is the wind speed averaged over the year
• D. Capacity factor is the amount of energy stored in batteries

Answer: (A)

Capacity factor is the ratio of the actual energy a wind farm produces over a period to the energy it would have produced if it ran at its full rated capacity for that same period. Because wind speeds vary and turbines undergo maintenance, the actual output is often well below the maximum, so the capacity factor is less than one. This matters for the electricity supply: a higher capacity factor means the farm delivers more of its potential output on average, improving reliability, forecasting, and how much backup or storage the grid needs. It also lowers the cost per kilowatt-hour since fixed costs are spread over more energy. A lower capacity factor implies less energy from the same installation and greater need for backup capacity to meet demand. The other interpretations—installed capacity, annual wind speed, or energy stored in batteries—don’t describe what capacity factor measures.