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.

Last updated: September 2026

Average Wind Speed (m/s)

Cut-in Wind Speed (m/s)

Rated Wind Speed (m/s)

Cut-out Wind Speed (m/s)

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Formula below · 2 sources (energy.gov, Wikipedia) · Updated Sep 2026

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About this calculator

A wind turbine's capacity factor (CF) is its average output as a share of rated power. Because power depends on the cube of wind speed and the wind is rarely at its average, CF cannot be read off the power curve at the mean speed. This calculator assumes a Rayleigh distribution of wind speeds (Weibull shape k = 2, scale c = 2 × mean / √π), the standard default for sites without measured data, and an idealized power curve: zero below cut-in, (v³ − cut-in³) / (rated³ − cut-in³) between cut-in and rated speed, full rated power between rated and cut-out, and zero above cut-out. CF = Σ powerFraction(v) × probability(v) over 0.05 m/s steps. Annual energy yield is then CF × ratedPower × 8,760 hours. Real power curves, turbulence, availability and wake losses typically reduce the result by a further 10–20%. Typical onshore capacity factors range from 25–40%, while offshore sites can exceed 50%.

How to use

Suppose a turbine has a cut-in speed of 3 m/s, a rated speed of 12 m/s, a cut-out speed of 25 m/s, and the site average wind speed is 8 m/s. The Rayleigh scale is c = 2 × 8 / √π ≈ 9.03 m/s. Weighting the power curve by the probability of each speed gives a capacity factor of about 37.8%. Reading the curve at the mean speed instead — (8³ − 3³) / (12³ − 3³) = 0.285, or the linear (8 − 3) / (12 − 3) = 0.556 — would misstate it badly. For context, a 2 MW turbine at 37.8% would generate about 0.378 × 2,000 kW × 8,760 h ≈ 6.6 GWh per year before availability and wake losses.

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.