Wind and water power result from the convective action of the sun, the rotation of the earth, and the evaporation of water. The radiant energy of the sun heats the earth's atmosphere, creating thermal updrafts which, in effect, turn that energy into the mechanical energy of the wind. The wind currents are then directed and magnified by the rotation of the earth. The resulting wind power was traditionally utilized in this country to sail ships, pump water and grind grain, but is now primarliy used to generate electricity.

Water that is evaporated by the sun rises with the thermal updrafts, is carried by the wind currents and then condenses and falls as rain into streams, rivers and lakes. As this water courses through streams and falls form higher to lower elevations, it creates the force, or head, that drives hydro turbines to create hydroelectric power.

For an index of manufacturers of wind and small-scale hydroelectric equipment and systems, see the Renewable Energy Manufacturers Index.