Measures the wind speed and transmits wind speed data to the controller. Most turbines have either two or three blades. A disc brake which can be applied mechanically, electrically, or hydraulically to stop the rotor in emergencies. Turbines cannot operate at wind speeds above about 65 mph because their generators could overheat. A cover protects the components inside the nacelle.
Some nacelles are large enough for a technician to stand inside while working.
Blades are turned, or pitched, out of the wind to keep the rotor from turning in winds that are too high or too low to produce electricity. The blades and the hub together are called the rotor. Because wind speed increases with height, taller towers enable turbines to capture more energy and generate more electricity. Measures wind direction and communicates with the yaw drive to orient the turbine properly with respect to the wind. Downwind turbines don't require a yaw drive, the wind blows the rotor downwind.