Why lightning likes wind turbines

Ars Technica : Wind turbines appear to be struck by lightning more frequently than buildings and other towers of similar height. To understand why, an international team of researchers built a radio sensor array around a series of wind farms in Spain and made a three-dimensional map of the radio emissions from lightning. One of the phenomena they recorded was regular low-energy discharges above the turbines as each blade passed through its highest point. They also saw an unusual, ground-to-cloud-to-ground strike in which a negative charge reached up from a turbine to a cloud. Normal strikes pass from cloud to ground and involve fingers of positive charge emitted by a ground-based object. The researchers tied the various events to the fact that the turbines are made of electrical insulators, which build up static charges as the blades pass through the air at high speeds. The rotation may also cause the blades to outrun the ionized air that would otherwise serve as a buffer preventing the discharge of static electricity. Understanding why lightning tends to strike wind turbines will help wind-farm operators better protect the turbines during poor weather.