Cut-in and cut-out wind speed

Cut-in is the wind speed at which a turbine begins producing usable power, typically around three to four meters per second. Below it the available energy does not cover the losses of turning the drivetrain, so the machine idles. Cut-out is the upper limit, commonly around twenty-five meters per second, above which the turbine shuts down or moves into a reduced-output storm mode to keep loads within design limits.

Both are control settings rather than physical constants, and both have drifted over the last decade. Storm control strategies that ramp output down gradually instead of tripping offline have replaced hard cut-out on many modern machines, because a hard stop in a storm surrenders the windiest hours of the year and imposes a large load cycle on the way down.

For analysis, the edges of the window are where records get noisy. Data close to cut-in has a poor signal-to-noise ratio because the power curve is steep and the wind is marginal, and data above cut-out is a shutdown rather than a performance measurement. A model that does not treat those regions separately will read normal control behavior as underperformance.

Cut-out behavior is also a common source of an apparent fleet anomaly that is not one. If two turbines on a site carry different storm control configurations, they will diverge sharply in high winds for entirely legitimate reasons, and only a comparison that knows the configuration will avoid raising a fault code investigation over a settings difference.