What is hydroelectric power?

Hydroelectric power is electricity produced by generators driven by turbines. These turbines convert the potential energy of falling or fast-flowing water into mechanical energy. Hydroelectric power was the most widely used form of renewable energy at the start of the 21st century. Water is collected or stored at a high elevation and led downward through pipes to a lower elevation. The falling water rotates turbines, which in turn drive generators that convert the mechanical energy into electricity. Hydroelectric power plants are often located in dams that impound rivers.

How does water produce electricity in a hydroelectric power plant?

In a hydroelectric power plant , electricity is produced from generators driven by turbines. The potential energy of falling or fast-flowing water is converted into mechanical energy. Water is collected or stored at a high elevation and led downward through pipes or tunnels to a lower elevation. The difference in elevation is the head. The falling water causes turbines to rotate, which in turn drive generators, converting the mechanical energy into electricity. Transformers convert the voltage, making it suitable for long-distance transmission. The structure that houses the turbines and generators is called the powerhouse.

What are the main parts of a hydroelectric power station?

A hydroelectric power station converts the potential energy of flowing water into electricity. The main components include: A dam to raise the water level and create a reservoir, increasing the water head (height). Penstocks or tunnels to channel water from the reservoir to the turbines. Turbines that rotate as water passes through them, converting the water's kinetic energy into mechanical energy. Generators, driven by the turbines, which convert mechanical energy into electrical energy. Transformers to convert the generator's alternating voltage to a higher voltage, suitable for long-distance transmission. A powerhouse, which is the structure housing the turbines and generators.

Why are dams important for hydroelectric power?

Dams are crucial for hydroelectric power because they facilitate electricity generation from the potential energy of water. Dams raise the water level of a river to create a reservoir , which increases the head (the height difference between the water surface and the turbines). The raised water is then funneled downwards at high pressure to spin turbines, which in turn drive generators to produce high-voltage electricity. Moreover, dams can also control the flow of water to ensure a consistent supply for power generation.

What are the advantages and disadvantages of hydroelectric power?

Hydroelectric power plants utilize the potential energy of flowing water, converting it into mechanical energy via turbines, which then drive generators to produce electricity. Hydroelectric power offers several advantages, as it is a continually renewable energy source that doesn't cause thermal pollution. It can also meet peak electricity demands and pairs well with other renewable energies. However, constructing dams can have negative environmental impacts, such as disturbing natural systems, blocking migrating fish, and displacing ecological and human communities. Dams can also be vulnerable to water scarcity. The high initial costs and the lack of available reservoirs can also be disadvantages.

How does hydroelectric power impact the environment and local communities?

Hydroelectric power, derived from the potential energy of flowing water, stands as a prominent renewable energy source. However, its environmental impact is considerable. Dam construction, crucial for hydroelectric plants, can disrupt fish migration and submerge ecosystems and communities as reservoirs fill. Despite these drawbacks, hydroelectric power offers advantages. It doesn't cause thermal pollution, and pumped-storage stations efficiently manage power loads. Technologies like fish ladders and locks aim to mitigate harm to fish populations, showcasing efforts to balance energy needs with ecological concerns.

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Hydroelectric dam at Imatrankoski spans the Vuoksi River in Finland, with turbulent water flowing through open spillways and forested banks on both sides.

Row of large blue hydroelectric turbine generators inside the Hoover Dam power plant, with an American flag hanging above.

Aerial view of Hoover Dam spanning the Colorado River between steep rocky cliffs in Black Canyon, with Lake Mead behind the dam and arid mountains surrounding the area.

This diagram shows how a tidal power barrage generates electricity, with cross-sections of a structure containing sluice gates and a turbine placed between the ocean and a tidal basin. Water flows through the turbine as tides change, converting tidal energy into hydroelectric power. The upper image depicts high tide with water held in the tidal basin, while the lower image shows water flowing back through the turbine at low tide.

Norris Dam stretches across a wide river, with a road running along the top and a power station below, surrounded by forested hills in East Tennessee.

The Transition to Renewable Energy Explained by Phil the Fixer

Congo River: hydroelectric dam at Inga Falls

Hydroelectic plant on Summersville Lake, near Summersville, W.Va.

Hydroelectric power station dam on the Volkhov River in Volkhov, Russia, with water cascading through multiple gates and trees in the background.

At a Glance

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Also called:: hydropower

Key People:: Jamsetji Tata

Related Topics:: renewable energy; power; waterpower; pumped-storage system

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hydroelectric power

renewable energy

Also known as: hydropower

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Last updated

Oct. 2, 2026 •History

Dams and hydroelectricity

For the generation of hydroelectric power at dams, water is collected or stored at a higher elevation and led downward through large pipes or tunnels (penstocks) to a lower elevation; the difference in these two elevations is known as the head. At the end of its passage down the pipes, the falling water causes turbines to rotate. The turbines in turn drive generators, which convert the turbines’ mechanical energy into electricity. Transformers are then used to convert the alternating voltage suitable for the generators to a higher voltage suitable for long-distance transmission. The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the powerhouse.

Hydroelectric power plants are usually located in dams that impound rivers, thereby raising the level of the water behind the dam and creating as high a head as is feasible. The potential power that can be derived from a volume of water is directly proportional to the working head, so that a high-head installation requires a smaller volume of water than a low-head installation to produce an equal amount of power. In some dams, the powerhouse is constructed on one flank of the dam, part of the dam being used as a spillway over which excess water is discharged in times of flood. Where the river flows in a narrow steep gorge, the powerhouse may be located within the dam itself.

James Watt as a young man, c1769. Scottish engineer and instrument maker. Invented the modern steam engine which became the main source of power in Britain's textile mills. His engine had a separate condenser in which steam from the cylinder; (see notes)

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In most communities the demand for electric power varies considerably at different times of the day. To even the load on the generators, pumped-storage hydroelectric stations are occasionally built. During off-peak periods, some of the extra power available is supplied to the generator operating as a motor, driving the turbine to pump water into an elevated reservoir. Then, during periods of peak demand, the water is allowed to flow down again through the turbine to generate electrical energy. Pumped-storage systems are efficient and provide an economical way to meet peak loads.

Tidal and wave power

In certain coastal areas, such as the Rance River estuary in Brittany, France, hydroelectric power plants have been constructed to take advantage of the rise and fall of tides. When the tide comes in, water is impounded in one or more reservoirs. At low tide, the water in these reservoirs is released to drive hydraulic turbines and their coupled electric generators (see tidal power).

Similarly, wave power generates electricity by harnessing the up-and-down motion of ocean waves. Wave power is typically produced by floating turbine platforms or buoys that rise and fall with the swells. The world’s first operational wave power generator is located off the coast of Aguçadora, Portugal, and produces as much as 2.25 megawatts from three huge jointed tubes that float on the surface of the Atlantic Ocean (see wave power).

Advantages and disadvantages

Falling water is one of the three principal sources of energy used to generate electric power, the other two being fossil fuels and nuclear fuels. Hydroelectric power has certain advantages over these other sources. It is continually renewable owing to the recurring nature of the hydrologic cycle. It does not produce thermal pollution. (However, some dams can produce methane from the decomposition of vegetation under water.) Hydroelectric power from dams is a preferred energy source in areas with heavy rainfall and with hilly or mountainous regions that are in reasonably close proximity to the main load centers. Some large hydro sites that are remote from load centers may be sufficiently attractive to justify the long high-voltage transmission lines. Small local hydro sites may also be economical, particularly if they combine storage of water during light loads with electricity production during peaks.

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Many of the negative environmental impacts of hydroelectric power come from the associated dams, which can interrupt the migrations of spawning fish, such as salmon, and permanently submerge or displace ecological and human communities as the reservoirs fill. A movement to decommission and remove hydroelectric dams in sensitive ecological areas has grown in the 21st century. In addition, hydroelectric dams are vulnerable to water scarcity. In August 2021 Oroville Dam, one of the largest hydroelectric power plants in California, was forced to shut down due to historic drought conditions in the region.

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