Rated power

Rated power is the nameplate figure: 3.6 MW, 6 MW, 15 MW. It is the output the machine is designed to sustain once the wind reaches rated speed, typically somewhere between twelve and fifteen meters per second, and it is held constant above that point by pitching the blades to shed the surplus.

Above rated wind speed a turbine is deliberately throwing energy away, because the drivetrain and the generator cannot take more. This is why the flat top of a power curve is the least informative part of it for performance work: two machines in very different condition will both sit at rated output in a strong wind, and the difference between them only appears in the sloped section below.

Rated power is also the denominator of capacity factor, which is why capacity factor falls when a manufacturer fits a larger rotor to the same generator. The machine produces more energy and reports a lower percentage, and the two facts are not in conflict - one is a measurement of output and the other is a ratio against a nameplate.

For an operator, the practically important number is not the rating but the hours spent below it. Nearly all recoverable loss lives in the partial-load region, which is where a control error, yaw misalignment, or a degrading blade changes what the machine produces.