Harnessing Hydroelectric Energy: Dams

One method for harnessing hydroelectric energy is a dam, or impoundment facility.

While water wheels extract some of a stream's power, it was discovered that much more power could be extracted if pressure could be built up. One cannot accumulate pressure in a running stream, but when a dam is built, the water piles up behind the dam so—at the base of the dam—the pressure is increased dramatically. When released, the pressurized water shoots down the penstock and through a system of propellers called a turbine.

The water that is piled up behind the dam has gravitational potential energy, since it can do work as it falls downward. This work is used by spinning the turbine, which gains kinetic energy. As the generator makes electricity, this kinetic energy is converted to electrical potential energy, which is then transported to homes and businesses for use in light bulbs, refrigerators, and the like.