Hydroelectric Power

Like the sun and the wind, water has been serving the industry of humankind for at least as long as we’ve been recording history. In Himalayan villages in the twelfth century, small hydro systems powering waterwheels to grind grain would have been a common feature of the landscape. The first hydroelectric power plant was built in Appleton, Wisconsin, in 1882. It generated just 12.5 kilowatts of power, enough to provide lights for two small paper mills and one house. Today hydroelectric power is a form of renewable energy so mainstream that often it’s not even included in state or national tallies of renewable power capacity.

One of the reasons why hydroelectric power has such a comfortable niche in our contemporary energy mix is the lockstep progress of hydro technology and the electrification of developed countries. It’s been around for a long time: FDR, the father of American electrification, who called for hydroelectric power to be expanded in the 1930s as a source of cheap, clean electricity.

Nowadays hydroelectric giants, such as the 7,600-megawatt Grand Coulee power station on the Columbia River in the state of Washington and the 13,000-megawatt Itaipu Dam on the Paraná River in Brazil, combine to provide 24 percent of the world’s electricity. The global capacity from all hydroelectric facilities is 675,000 megawatts producing 2.9 trillion kilowatt-hours of power annually and—not incidentally—saving the world the equivalent of 1.7 billion barrels of oil each and every year.

Hydroelectric power works by converting the energy in flowing water to electric 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, and the strength of the natural pressure of the surging water is 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.

Though the typical arrangement of all hydroelectric stations is similar, there are several variations in how the design can be implemented. First of all, the amount of electricity any hydro system can produce is determined by its “head”—the difference in height between the surface of the water in the high reservoir and how far it must fall to reach the turbines in the power station below. The greater the height, the more power that is achievable. The height of a system’s head is determined as much by engineering feats as it is by the natural geological features of the chosen site.

Second, the water’s flow can be utilized in a variety of ways. Conventional hydroelectric power plants use a one-way flow of water. These sometimes are called run-of-the-river plants, meaning that they rely solely on the native flow of the body of water. Consequently, they are significantly affected by the weather and by seasonal changes in rainfall and water levels that can cause fluctuations in the amount of electricity they produce. Conventional hydroelectric systems, with one-way water flow, can also be designed as “storage” plants, which reserve enough water in their dams to offset seasonal impact on their water flow. Large dams can, in fact, store several years’ worth of water.

Other hydroelectric systems are designed as pumped storage plants. This means that after the naturally flowing water has produced an initial quantity of electricity, it’s 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. This characteristic of water—that it can be stored in dams or redirected for reuse—has probably also given hydroelectric power a historic advantage over the intermittent wind and sun and has likely contributed to its rapid acceptance and use as a mainstream power source.

Source: Green: Your Place in the Renewable Energy Revolution”, Palgrave-MacMillan, 2008


  • Hydropower is the most important and widely-used renewable source of energy.
  • Hydropower represents 19% of total electricity production worldwide.
  • Canada is the largest producer of hydroelectricity, followed by the United States and Brazil.
  • Approximately two-thirds of the economically feasible potential remains to be developed.
  • Untapped hydro resources are still abundant in Latin America, Central Africa, India and China.

Source: USGS.gov