Most machines that make electricity need some form of mechanical energy to get things started. Mechanical energy spins the generator to make the electricity. In the case of hydroelectricity, the mechanical energy comes from large volumes of falling water. For more than 100 years, the simplest way to produce the volumes of falling water needed to make electricity has been to build a dam. A dam stops the natural fl ow of a river, building up a deep reservoir behind it. However, large dams and reservoirs are not always appropriate, especially in the more ecologically sensitive areas of the planet.
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