Yaw misalignment

A turbine yaws to face the wind, using a nacelle anemometer and wind vane sitting behind the rotor. When that sensor is miscalibrated or its correction drifts, the machine settles at a consistent angle away from the true wind direction. Because the error is systematic rather than random, it costs energy every hour the turbine runs.

The loss scales roughly with the cosine of the misalignment angle raised to a power near three, so a handful of degrees is not trivial. A persistent offset of eight to ten degrees can cost a low single-digit percentage of annual energy on that machine; across a fleet, that is a meaningful amount of production lost to a calibration constant. Misalignment also loads the rotor asymmetrically, which shortens component life independently of the energy it costs.

What makes this the most attractive class of finding is that nothing is broken. No alarm fires, availability looks perfect, and the fix is a settings change rather than a crane. It is invisible precisely because the turbine believes it is behaving correctly, which is why it only surfaces when output is compared against a learned power curve rather than against the turbine's own view of itself.

Static misalignment - a fixed offset present across all conditions - is the version worth hunting first, because it is both the easiest to detect in a long operating record and the cheapest to correct. Dynamic error, where the yaw controller chases a shifting wind and never settles, is a different problem that usually points at control tuning or at high turbulence intensity.