The nacelle sits on top of the tower and contains main technical parts of the wind turbine. Usually made of fiberglass, the nacelle contains the low- and high-speed shafts, the gearbox, the brake and the generator. It also contains the blade pitch control, a hydraulic system that controls the angle of the blades, and the yaw drive, which controls the position of the turbine relative to the wind.
As the nacelle holds hardware which is responsible for transforming dynamic energy of the wind into electricity the typical weight of the nacelle structure can exceed 500 tons. Due to the sheer size of the housing panels sandwich structures are typically used for the nacelle walls using wet resin technologies and foam core materials. Hexcel has developed an optimized range of PUR foam core materials for nacelle construction.