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Hydroelectric power, commonly called 'hydropower,' creates electricity by the kinetic energy of water flowing downstream. Typically the water is directed through a turbine, which converts the water's energy to rotary energy, which is used to turn generators. There are dozens of different turbine designs to accommodate a variety of applications. 

Hydropower is clean and renewable, and in many ways an ideal way to generate electricity. Operators can vary the flow of water to meet changes in demand. The world's first hydroelectric plant opened in Appleton, Wisconsin in 1882. In the 1940's, it supplied about 40% of demand in the U.S.; today it is closer to 10%, supplying about 80,000 megawatts (MW) of conventional capacity.

There are three principal methods for generating hydropower. With impoundment, a river is dammed, creating a reservoir; a continuous flow of water is released through turbines, recreating the river downstream from the dam. Important side benefits of impoundment include recreation, water supply and flood control. Glenn Lake in Goffstown is an example of impoundment.

Diversion channels part of the river through a hydropower plant, letting the rest of the river run free. Amoskeag Falls in Manchester is an example. Pumped storage pumps water to a reservoir at a higher elevation during off-peak hours, and then releases it through turbines during periods of peak demand. The utility pays less for the off-peak electricity than it earns for the peak-demand electricity.

All the major hydropower sites in the USA have been developed. The U.S. Department of Energy has identified 5,677 small-scale sites in 49 states with an undeveloped capacity of about 30,000 MW. On the horizon are marine and hydrokinetic technologies -- wave, tidal, current and ocean thermal energy. You can learn more at