A wind turbine consists of a tall cylindrical tower with a nacelle (generator housing) on top which contains the functional components of the turbine. Attached to the nacelle are three blades which rotate, driven by the force of the wind. Turbine nacelles also rotate through 360 degrees in order to keep the blades facing into the wind. The specifications of turbines vary between manufacturers. Overall height from the sea level to the blade tip can reach over 300 meters (1000 feet). The turbine tower diameter is approximately 7-9 meters. Blade tips can reach speeds of 195 km/h when rotating.