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Hydroelectric power is the world’s largest producer of renewable energy. Through the conversion of the kinetic energy of flowing water into electricity, hydroelectric power provides a steady and reliable source of renewable energy.
The same physics lie behind the design of all hydroelectric systems: A dam is used to capture and store water; pipes, or penstocks, carry the water from a high reservoir, downhill, toward turbines in a power station, with the strength of the natural pressure of the surging water often increased by nozzles affixed to the end of the pipes; the water strikes the turbines, rotating them and driving a generator that produces electricity.

The water’s flow can be utilized in a variety of ways. Conventionalhydroelectric power plants use a one-way flow of water. Systems with one-way water flow can also be designed as “storage” plants, reserving enough water in their dams to offset seasonal impact on their water flow. Alternatively, “run-of-the-river” plants have limited or no reservoir capacity and rely on the natural flow of waterways to produce electricity.

Other hydroelectric systems are designed as “pumped storage” plants. This means that after the water has produced an initial quantity of electricity, it is diverted from the turbines into a lower reservoir below the dam. During off-peak hours, or through dry-weather conditions, the water in this lower reservoir can be pumped back up and reused to supply a steady stream of electricity to the plant’s customers during peak use times.

For more on hydroelectric power, visit the National Hydropower Association.


  • The U.S. has the second largest installed capacity of hydropower globally (including pumped storage), amounting to about 100 GW. (Environmental and Energy Study Institute (EESI))
  • The U.S. accounted for 9.4% the world’s hydropower consumption in 2011, a nearly 25% increase over 2010. (BP)
  • The U.S. hydropower industry could install 23,000 MW to 60,000 MW of new capacity by 2025 depending on policy changes. (National Hydropower Association (NHA))
  • In the U.S. alone, there is over 400 GW of untapped hydropower resource potential (inland and ocean). (NHA)
More in this category: « Ocean Waste »
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