Power curve

A power curve maps wind speed to electrical output: nothing below cut-in, a steep rise through the middle of the range, flat at rated power, and zero above cut-out. Manufacturers publish one per turbine model, measured under reference conditions.

The published curve is a specification rather than a description of your machine. Real turbines deviate from it through blade soiling and erosion, control settings, air density, terrain, and wake effects from neighbours - and the deviation grows with age. Judging a ten-year-old turbine against a datasheet curve therefore produces a number that is part equipment condition and part everything else, which is not actionable.

The alternative is a learned curve: build each turbine's expected output from its own operating history under matched conditions, then measure the live machine against itself. Underperformance becomes visible as a gap against a baseline that already accounts for where the turbine stands and what it has been through, rather than against an idealised machine that does not exist on your site. Persistent gaps are what predictive maintenance and yaw misalignment checks then explain.