Hydropower (also called hydroelectric power or hydroelectricity) is electricity generated by Earth's water cycle. Water evaporates from Earth's surface, forms clouds, precipitates back to Earth and flows toward the ocean. The movement of water as it flows downstream creates kinetic energy that can be converted into electricity. A hydroelectric power plant converts this energy into electricity by forcing water, often held at a dam, through a hydraulic turbine that is connected to a generator. The water exits the turbine and is returned to a stream or riverbed below the dam.
Hydropower is mostly dependent upon precipitation and elevation changes; high precipitation levels and large elevation changes are necessary to generate significant quantities of electricity. Because it is generated by Earth's natural water cycle, hydropower is considered a renewable energy resource. (Source: EPA / Photo: Flickr)