ABSTRACT
Before the industrial revolution, wind was a major source of power for pumping water, grinding grain, and long-distance transportation. During the 1930s, small wind systems with battery storage were installed in rural areas; however, these units were displaced with power from the electric grid through rural electric cooperatives. There were a number of attempts to build wind turbines for the utility grid; however, most operated only a short time due to technical and economic problems. Wind turbines are classified according to the interaction of the blades with the wind, orientation of the rotor axis with respect to the ground and to the tower and innovative or unusual types of machines. The power coefficient is the power out or power produced by the wind turbine divided by the power in the wind. From conservation of energy and momentum, the maximum theoretical efficiency of a rotor is 59%.
