Cut-out wind speed

At very high wind speeds the structural loads on blades, hub, tower and foundation grow faster than the extra energy is worth. The cut-out speed is the threshold where the controller pitches the blades to feather, applies the brake and yaws the rotor into a safe idling position.

The classic value for IEC Class I–III turbines is 25 m/s as a 10-minute average, with faster triggers on short gusts (for example a 3-second mean above 30–35 m/s). Some offshore and typhoon-class designs extend this to 28–34 m/s.

Hard cut-out causes a sudden drop from full power to zero. When storms pass across a region this can remove gigawatts within minutes, a recognised challenge for grid operators in Denmark and northern Germany. Most manufacturers now offer soft cut-out or storm ride-through: power is reduced gradually from about 22–25 m/s down to zero at 30–34 m/s using pitch control, which flattens the ramp and recovers some energy.

In energy terms cut-out rarely matters. Winds above 25 m/s occur well under 0.5% of the time at most sites under a typical Weibull distribution, so annual losses are usually below 1%. Restart occurs only after wind falls back below a lower hysteresis threshold, often 20–22 m/s.