Hydroelectricity

Hydroelectricity is the generation of electrical power from moving water. In 2023, it provided roughly 15% of the world's electricity—about 4,210 terawatt-hours—surpassing the combined output of all other renewable sources as well as nuclear power. Because it can deliver large amounts of low-carbon electricity on demand, hydropower is considered crucial for building clean and reliable power grids.

A hydroelectric station with a dam and reservoir can adjust its output in seconds or minutes to match fluctuating demand. Once built, such a facility produces no direct waste and typically emits far fewer greenhouse gases than fossil-fuel plants. However, when dams are constructed in lowland rainforests, the flooding of forested areas can release substantial greenhouse gases. The environmental costs are significant: loss of farmland, displacement of communities, disruption of river ecosystems, altered siltation and erosion patterns, and damage to habitats. While dams can reduce flood risks, a dam failure can be catastrophic.

By 2025, global installed hydropower capacity reached nearly 1,456 gigawatts—the highest of any renewable technology. Hydropower dominates electricity generation in countries like Brazil, Norway, and China, though its expansion is limited by geography and environmental concerns. Tidal power offers an alternative for coastal regions. In 2022, China added 24 GW of capacity, accounting for nearly three-quarters of global growth, while Europe added 2 GW—its largest annual increase since 1990. That same year, global hydropower generation rose by 70 TWh (2%), keeping it the largest renewable energy source, ahead of all other renewables combined.

**History** People have harnessed water for mechanical energy since at least 202 BC in Han-dynasty China. In the late 1700s, hydraulic power helped drive the Industrial Revolution. French engineer Bernard Forest de Bélidor’s *Architecture Hydraulique* (mid-1700s) described vertical- and horizontal-axis water machines. In 1771, Richard Arkwright combined water power, the water frame, and continuous production, shaping the factory system and modern labor practices. By the 1840s, hydraulic power networks were transmitting hydro energy to users.

The late 1800s saw the coupling of hydraulic power with newly developed electrical generators. The world’s first hydroelectric scheme—powering a single arc lamp in an art gallery—was built in 1878 at Cragside, England, by William Armstrong. The Schoelkopf Power Station No. 1 near Niagara Falls began generating electricity in 1881. On September 5, 1882, generators at St. Anthony Falls on the Mississippi River lit arc lamps along Washington Avenue in Minneapolis. The first Edison hydroelectric plant, the Vulcan Street Plant, started operating on September 30, 1882, in Appleton, Wisconsin, producing about 12.5 kilowatts. By 1886, there were 45 hydroelectric stations in the U.S. and Canada; by 1889, 200 in the U.S. alone.

In the early 1900s, commercial companies built many small hydro stations in mountains near cities. Grenoble, France, hosted the International Exhibition of Hydropower and Tourism in 1925, drawing over a million visitors. By 1920, hydroelectricity supplied 40% of U.S. power, prompting the Federal Power Act, which created the Federal Power Commission to regulate stations on federal land and water. As dams grew larger, they took on additional roles—flood control, irrigation, navigation—requiring federal funding. Agencies like the Tennessee Valley Authority (1933) and Bonneville Power Administration (1937) were formed, while the Bureau of Reclamation, already building irrigation projects, constructed large hydro projects such as Hoover Dam (1928). The U.S. Army Corps of Engineers completed Bonneville Dam in 1937 and was designated the lead federal flood control agency by the Flood Control Act of 1936.

Hydro stations kept growing throughout the 1900s, with hydropower often called “white coal.” Hoover Dam’s initial 1,345 MW plant was the world’s largest in 1936, surpassed by Grand Coulee Dam’s 6,809 MW in 1942. The Itaipu Dam (1984) in South America produced 14 GW, then was overtaken by China’s Three Gorges Dam (2008) at 22.5 GW. Today, hydropower supplies over 85% of electricity in countries like Norway, the Democratic Republic of the Congo, Paraguay, and Brazil.

**Future potential** In 2021, the International Energy Agency (IEA) stressed the need for more efforts to limit climate change. Some nations have already tapped most of their hydropower potential—Switzerland uses 88% of its capacity, Mexico 80%. In 2022, the IEA forecast an increase of 141 GW in hydropower capacity between 2022 and 2027, a figure slightly lower than previous projections.