Large Wind Turbine

Power curve of a wind turbine

At very low wind speeds, the rotor of a wind turbine will stay still. At the cut-in wind speed (typically 3 to 4 m/s), the rotor starts to rotate and the wind turbine will start generating power. As the wind gets stronger and stronger, the power output will increase and when the rated wind speed (or "nominal wind speed") is reached, the wind turbine will deliver its rated output power (or "nominal output"). After that, the output power will more or less flat off and at the cut-out speed, the wind turbine will brake and deliver no output at all so as to protect itself from possible damage.

The performance of a wind turbine is expressed by its power curve which shows the relationship between the power output of the turbine at different wind speeds, from cut-in to cut-off.

Above: Power curves at different sound levels of V52-850 kW wind turbine (the sound level is adjusted by means of varying the rotation speed of the wind turbine)
(Source: Vestas)

In order to select a suitable wind turbine for a specific site, a general approach is to make use of the power curves of individual wind turbines and the wind data for the site to conduct energy yield prediction. (More information on this aspect is given in the Large Wind Turbine - Resource Potential section.)