Waterfalls like this one contain a great deal of energy, making hydropower the most widely-used renewable energy source. Credit: Jim Miller; Courtesy DOE/NREL

Hydroelectric systems make use of the energy in running water to create electricity. In coal and natural gas systems, a fossil fuel is burned to heat water. The steam pressure from the boiling water turns "propellors" called turbines. These turbines spin coils of wire between magnets to produce electricity. Hydropowered systems also make use of turbines to generate electrical power; however, they do so by using the energy in moving water to spin the turbines.

Water has kinetic energy when it flows from higher elevations to lower elevations. The energy spins turbines like those pictured below.

An interior view of the turbines at "Nine Mile Plant" at the Spokane River

A Hydroelectric Turbine courtesy of DOE

In larger scale hydroelectric plants, large volumes of water are contained by dams near the generator and turbines. The "forebay" is a storage area for water that must be deep enough that the penstock is completely submerged. The water is allowed to flow into the electricity-generating system through a passage called the "penstock". The controlled high-pressure water spins the turbines, allowing the generator to produce an electric current. The "powerhouse" contains and protects the equipment for generating electricity. The high-pressure water exits the system through a "draft tube." The "fish ladder" (see "problems") attempts to minimize the environmental impact of hydroelectric systems by providing a path for migrating fish to take.