Wind Energy Capacity Factor Calculator
Estimates a wind turbine's capacity factor — the ratio of actual output to maximum possible output — and annual energy yield. Use it when evaluating a site's wind resource or comparing turbine performance specifications.
About this calculator
A wind turbine's capacity factor (CF) describes how efficiently it converts available wind into electricity over time. The turbine only generates power when wind speed sits between its cut-in speed and cut-out speed. Within that range, output scales linearly from zero at cut-in up to full rated power at rated speed. The formula used here is: CF = clamp((averageWindSpeed − cutInSpeed) / (ratedSpeed − cutInSpeed), 0, 1) × (1 if averageWindSpeed < cutOutSpeed, else 0). Annual energy yield (AEY) is then AEY = CF × ratedPower × 8,760 hours. Typical onshore capacity factors range from 25–40%, while offshore sites can exceed 50%, reflecting stronger and more consistent winds.
How to use
Suppose a turbine has a cut-in speed of 3 m/s, rated speed of 12 m/s, cut-out speed of 25 m/s, rated power of 2,000 kW, and the site average wind speed is 8 m/s. Step 1 — check cut-out: 8 < 25, so the turbine operates. Step 2 — calculate CF: (8 − 3) / (12 − 3) = 5 / 9 ≈ 0.556 (55.6%). Step 3 — annual energy yield: 0.556 × 2,000 kW × 8,760 h ≈ 9,740,160 kWh (≈ 9.74 GWh per year). Enter your own values to size a real installation.
Frequently asked questions
What is a good capacity factor for a wind turbine?
Onshore wind turbines typically achieve capacity factors between 25% and 40%, depending on site wind resources and turbine design. Offshore installations often reach 45–55% because ocean winds are stronger and more consistent. A capacity factor below 20% generally signals a poor wind resource or an oversized turbine for the site. Developers use this metric alongside levelized cost of energy (LCOE) to judge project viability.
How does cut-in speed affect wind turbine energy output?
Cut-in speed is the minimum wind speed at which a turbine starts generating usable electricity, typically 2.5–4 m/s for modern machines. Any wind below this threshold produces no power, so sites with frequent low-wind periods see reduced annual yield. Lowering cut-in speed through turbine design improvements can meaningfully increase energy capture at low-wind sites. However, gains must be weighed against added mechanical complexity and cost.
Why does a wind turbine shut down above cut-out speed?
Above the cut-out speed (usually 20–25 m/s), wind loads on the rotor and nacelle become dangerously high, risking structural damage or catastrophic failure. The turbine feathers its blades and brakes to a stop to protect itself. Some modern turbines use 'storm control' modes that reduce rather than fully halt generation in high winds, extending operational range. Once wind drops back below cut-out speed the turbine automatically restarts.