Hydroelectricity, or hydroelectric power, is electricity generated from

hydropower Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, ...

(water power). Hydropower supplies 15% of the world's

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

, almost 4,210

TWh TWH or twh could refer to: * Tai Dón language, a language of Vietnam, Laos, and China * Tai Wo Hau station, Hong Kong; MTR station code * Tennessee Walking Horse, a breed of horse * Toronto Western Hospital, a hospital in Toronto, Canada * Tun ...

in 2023, which is more than all other

renewable source Renewable energy (also called green energy) is energy made from renewable resource, renewable natural resources that are replenished on a human lifetime, human timescale. The most widely used renewable energy types are solar energy, wind pow ...

s combined and also more than

nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by ...

. Hydropower can provide large amounts of

low-carbon electricity Low-carbon electricity or low-carbon power is electricity produced with substantially lower greenhouse gas emissions over the entire lifecycle than power generation using fossil fuels. The energy transition to low-carbon power is one of the m ...

on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less

greenhouse gas Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...

than

fossil fuel A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geolog ...

-powered energy plants.Renewables 2011 Global Status Report, page 25, Hydropower
''

REN21 REN21 (Renewable Energy Policy Network for the 21st Century) is a policy network and a multistakeholder governance group which is focused on renewable energy policy. REN21's goal is to facilitate policy development, knowledge exchange, and joint ...

'', published 2011, accessed 2016-02-19. However, when constructed in lowland

rainforest Rainforests are forests characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropi ...

areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted. Construction of a hydroelectric complex can have significant environmental impact, principally in loss of

arable land Arable land (from the , "able to be ploughed") is any land capable of being ploughed and used to grow crops.''Oxford English Dictionary'', "arable, ''adj''. and ''n.''" Oxford University Press (Oxford), 2013. Alternatively, for the purposes of a ...

and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding,

dam failure A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than ...

can be catastrophic. In 2021, global installed hydropower electrical capacity reached almost 1,400 GW, the highest among all renewable energy technologies.December 2022,
Renewables 2022
, IEA, Paris, license: CC BY 4.0. Hydroelectricity plays a leading role in countries like Brazil, Norway and China. but there are geographical limits and environmental issues.

Tidal power Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods. Although not yet widely used, tidal energy has the potential for future electricity generation. T ...

can be used in coastal regions. China added 24 GW in 2022, accounting for nearly three-quarters of global hydropower capacity additions. Europe added 2 GW, the largest amount for the region since 1990. Meanwhile, globally, hydropower generation increased by 70 TWh (up 2%) in 2022 and remains the largest renewable energy source, surpassing all other technologies combined.

History

Hydropower has been used since ancient times to grind flour and perform other tasks. In the late 18th century hydraulic power provided the energy source needed for the start of the

Industrial Revolution The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...

. In the mid-1700s, French engineer

Bernard Forest de Bélidor Bernard Forest de Bélidor (1698, Catalonia, Spain – 8 September 1761, Paris, France) was a French engineer, significant to the development of the science of hydraulics and ballistics. He was the son of Jean Baptiste Foret de Belidor, an offic ...

published ''Architecture Hydraulique'', which described vertical- and horizontal-axis hydraulic machines, and in 1771

Richard Arkwright Sir Richard Arkwright (23 December 1732 – 3 August 1792) was an English inventor and a leading entrepreneur during the early Industrial Revolution. He is credited as the driving force behind the development of the spinning frame, known as ...

's combination of

water power Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to produce electricity or to power machines. This is achieved by converting the gravitational potential or kin ...

, the

water frame The water frame is a spinning frame that is powered by a water-wheel. History Richard Arkwright, who patented the technology in 1769, designed a model for the production of cotton thread, which was first used in 1765. The Arkwright water f ...

, and

continuous production Continuous production is a flow production method used to manufacture, produce, or process materials without interruption. Continuous production is called a continuous process or a continuous flow process because the materials, either dry bu ...

played a significant part in the development of the factory system, with modern employment practices. In the 1840s,

hydraulic power network A hydraulic power network is a system of interconnected Pipe (fluid conveyance), pipes carrying pressurized liquid used to transmit Power (physics), mechanical power from a power source, like a pump, to hydraulic equipment like lifts or Hydrauli ...

s were developed to generate and transmit hydro power to end users. By the late 19th century, the

electrical generator In electricity generation, a generator, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an extern ...

was developed and could now be coupled with hydraulics. The growing demand arising from the

would drive development as well. In 1878, the world's first hydroelectric power scheme was developed at

Cragside Cragside is a Victorian era, Victorian Tudor Revival architecture, Tudor Revival country house near the town of Rothbury in Northumberland, England. It was the home of William Armstrong, 1st Baron Armstrong, founder of the Armstrong Whitworth a ...

Northumberland Northumberland ( ) is a ceremonial counties of England, ceremonial county in North East England, on the Anglo-Scottish border, border with Scotland. It is bordered by the North Sea to the east, Tyne and Wear and County Durham to the south, Cumb ...

, England, by William Armstrong. It was used to power a single

arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...

in his art gallery. The old Schoelkopf Power Station No. 1, US, near

Niagara Falls Niagara Falls is a group of three waterfalls at the southern end of Niagara Gorge, spanning the Canada–United States border, border between the Provinces and territories of Canada, province of Ontario in Canada and the state of New York (s ...

, began to produce electricity in 1881. The first Edison hydroelectric power station, the

Vulcan Street Plant The Vulcan Street Plant was the first Edison hydroelectric central station.Appleton, Wisconsin Appleton () is the county seat of Outagamie County, Wisconsin, United States, with small portions extending into Calumet County, Wisconsin, Calumet and Winnebago County, Wisconsin, Winnebago counties. Located on the Fox River (Green Bay tributary ...

, with an output of about 12.5 kilowatts. By 1886 there were 45 hydroelectric power stations in the United States and Canada; and by 1889 there were 200 in the United States alone. At the beginning of the 20th century, many small hydroelectric power stations were being constructed by commercial companies in mountains near metropolitan areas.

Grenoble Grenoble ( ; ; or ; or ) is the Prefectures in France, prefecture and List of communes in France with over 20,000 inhabitants, largest city of the Isère Departments of France, department in the Auvergne-Rhône-Alpes Regions of France, region ...

, France held the International Exhibition of Hydropower and Tourism, with over one million visitors 1925. By 1920, when 40% of the power produced in the United States was hydroelectric, the

Federal Power Act The Federal Power Act is a law appearing in Chapter 12 of Title 16 of the United States Code, entitled "Federal Regulation and Development of Power". Enacted as the Federal Water Power Act on June 10, 1920, and amended many times since, its orig ...

was enacted into law. The Act created the

Federal Power Commission The Federal Power Commission (FPC) was an independent commission of the United States government, originally organized on June 23, 1930, with five members nominated by the president and confirmed by the Senate. The FPC was originally created in ...

to regulate hydroelectric power stations on federal land and water. As the power stations became larger, their associated dams developed additional purposes, including

flood control Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and ru ...

irrigation Irrigation (also referred to as watering of plants) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has bee ...

and

navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...

. Federal funding became necessary for large-scale development, and federally owned corporations, such as the

Tennessee Valley Authority The Tennessee Valley Authority (TVA) is a federally owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, and small areas of Georgia, North Carolin ...

(1933) and the

Bonneville Power Administration The Bonneville Power Administration (BPA) is an American federal agency operating in the Pacific Northwest. BPA was created by an act of United States Congress, Congress in 1937 to market electric power from the Bonneville Dam located on the Col ...

(1937) were created. Additionally, the

Bureau of Reclamation The Bureau of Reclamation, formerly the United States Reclamation Service, is a List of United States federal agencies, federal agency under the U.S. Department of the Interior, which oversees water resource management, specifically as it ...

which had begun a series of western US irrigation projects in the early 20th century, was now constructing large hydroelectric projects such as the 1928

Hoover Dam The Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado, Black Canyon of the Colorado River (U.S.), Colorado River, on the border between the U.S. states of Nevada and Arizona. Constructed between 1931 and 1936, d ...

. The

United States Army Corps of Engineers The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil wo ...

was also involved in hydroelectric development, completing the

Bonneville Dam Bonneville Lock and Dam consists of several run-of-the-river dam structures that together complete a span of the Columbia River between the U.S. states of Oregon and Washington at River Mile 146.1. The dam is located east of Portland, Ore ...

in 1937 and being recognized by the

Flood Control Act of 1936 The Flood Control Act of 1936, , (FCA 1936) was an Act of Congress, Act of the United States Congress signed into law by President of the United States, President Franklin D. Roosevelt, Franklin Delano Roosevelt on 22 June 1936.

as the premier federal flood control agency.The Evolution of the Flood Control Act of 1936, Joseph L. Arnold

, 1988 Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as "white coal".

's initial power station was the world's largest hydroelectric power station in 1936; it was eclipsed by the

Grand Coulee Dam Grand Coulee Dam is a concrete gravity dam on the Columbia River in the U.S. state of Washington, built to produce hydroelectric power and provide irrigation water. Constructed between 1933 and 1942, Grand Coulee originally had two powerhous ...

in 1942. The

Itaipu Dam The Itaipu Dam ( ; ; ) is a hydroelectric dam on the Paraná River located on the border between Brazil and Paraguay. It is the third largest hydroelectric dam in the world, and holds the 45th largest reservoir in the world. The name "Itai ...

opened in 1984 in South America as the largest, producing , but was surpassed in 2008 by the

Three Gorges Dam The Three Gorges Dam (), officially known as Yangtze River Three Gorges Water Conservancy Project () is a hydroelectric gravity dam that spans the Yangtze River near Sandouping in Yiling District, Yichang, Hubei province, central China, downs ...

in China at . Hydroelectricity would eventually supply some countries, including

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

Democratic Republic of the Congo The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

and

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, with over 85% of their electricity.

Future potential

In 2021 the International Energy Agency (IEA) said that more efforts are needed to help limit climate change. Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%. In 2022, the IEA released a main-case forecast of 141 GW generated by hydropower over 2022–2027, which is slightly lower than deployment achieved from 2017–2022. Because environmental permitting and construction times are long, they estimate hydropower potential will remain limited, with only an additional 40 GW deemed possible in the accelerated case.

Modernization of existing infrastructure

In 2021 the IEA said that major modernisation refurbishments are required.

Generating methods

Conventional (dams)

Most hydroelectric power comes from the

potential energy In physics, potential energy is the energy of an object or system due to the body's position relative to other objects, or the configuration of its particles. The energy is equal to the work done against any restoring forces, such as gravity ...

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

med water driving a

water turbine A water turbine is a rotary machine that converts kinetic energy and potential energy of water into mechanical work. Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now, t ...

and generator. The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...

. A large pipe (the "

penstock A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydro turbines and sewerage systems. The term is of Scots origin, and was inherited from the earlier technology of mill pond ...

") delivers water from the

to the turbine.

Pumped-storage

This method produces electricity to supply high peak demands by moving water between

s at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir, thus providing

demand side response In economics, demand is the quantity of a good that consumers are willing and able to purchase at various prices during a given time. In economics "demand" for a commodity is not the same thing as "desire" for it. It refers to both the desire to p ...

. When the demand becomes greater, water is released back into the lower reservoir through a turbine. In 2021 pumped-storage schemes provided almost 85% of the world's 190 GW of

grid energy storage Grid energy storage, also known as large-scale energy storage, are technologies connected to the electrical power grid that store energy for later use. These systems help balance supply and demand by storing excess electricity from variabl ...

and improve the daily

capacity factor The net capacity factor is the unitless ratio of actual electrical energy output over a given period of time to the theoretical maximum electrical energy output over that period. The theoretical maximum energy output of a given installation is def ...

of the generation system. Pumped storage is not an energy source, and appears as a negative number in listings.

Run-of-the-river

Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that only the water coming from upstream is available for generation at that moment, and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river.

Tide

tidal power Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods. Although not yet widely used, tidal energy has the potential for future electricity generation. T ...

station makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water's

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

or undammed sources such as undershot

water wheel A water wheel is a machine for converting the kinetic energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wheel (usually constructed from wood or metal), with numerous b ...

s. Tidal power is viable in a relatively small number of locations around the world.

Conduit

Conduit hydroelectricity stations use mechanical energy of water as part of the water delivery system through man-made conduits to generate electricity. Generally, the conduits are existing water

pipelines A pipeline is a system of pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countries around the world. The Un ...

such as in

public water supply Water supply is the provision of water by public utilities, commercial organisations, community endeavors or by individuals, usually via a system of pumps and pipes. Public water supply systems are crucial to properly functioning societies. Thes ...

. Some definitions expand the definition of conduits to be existing tunnels, canals, or aqueducts that are used primarily for other water delivery purposes than electricity generation.

Sizes, types and capacities of hydroelectric facilities

The classification of hydropower plants starts with two top-level categories: * small hydropower plants ( SHP) and * large hydropower plants (LHP). The classification of a plant as an SHP or LHP is primarily based on its

nameplate capacity Nameplate capacity, also known as the rated capacity, nominal capacity, installed capacity, maximum effect or gross capacity,low-head hydro power plant with

hydrostatic head When generating hydropower, the head is the distance that a given water source has to fall before the point where power is generated. Ultimately the force responsible for hydropower is gravity, so a hydroelectricity plant with a tall/high head can ...

of few meters to few tens of meters can be classified either as an SHP or an LHP. The other distinction between SHP and LHP is the degree of the water flow regulation: a typical SHP primarily uses the natural water discharge with very little regulation in comparison to an LHP. Therefore, the term SHP is frequently used as a synonym for the run-of-the-river power plant.

Large facilities

The largest power producers in the world are hydroelectric power stations, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations. Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundred

megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...

s are generally considered large hydroelectric facilities. Currently, only seven facilities over () are in operation worldwide, see table below.

Small

Small hydro is

hydroelectric power Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...

on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10

s (MW) is generally accepted as the upper limit. This may be stretched to and in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

and the United States. Nw vietnam hydro

Small hydro stations may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a grid, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on the balance between stream flow and power production.

Micro

Micro hydro means

installations that typically produce up to of power. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks. There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel. Micro hydro systems complement

photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...

solar energy systems because in many areas water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum.

Pico

Pico hydro is

generation of under . It is useful in small, remote communities that require only a small amount of electricity. For example, the 1.1 kW Intermediate Technology Development Group Pico Hydro Project in Kenya supplies 57 homes with very small electric loads (e.g., a couple of lights and a phone charger, or a small TV/radio). Even smaller turbines of 200–300 W may power a few homes in a developing country with a drop of only . A Pico-hydro setup is typically

run-of-the-river Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amou ...

, meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream.

Underground

underground power station An underground power station is a type of hydroelectric power station constructed by excavating the major components (e.g. machine hall, penstocks, and tailrace) from rock, rather than the more common surface-based construction methods. One or mo ...

is generally used at large facilities and makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake. A tunnel is constructed to take water from the high reservoir to the generating hall built in a cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway. Tailrace-Forebay-Limestone

Calculating available power

A simple formula for approximating electric power production at a hydroelectric station is:

P = -\eta \ (\dot g \ \Delta h) = -\eta \ ((\rho \dot) \  g \ \Delta h)

where *

P

power Power may refer to: Common meanings * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power, a type of energy * Power (social and political), the ability to influence people or events Math ...

(in

watt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...

s) *

\eta

(

eta Eta ( ; uppercase , lowercase ; ''ē̂ta'' or ''ita'' ) is the seventh letter of the Greek alphabet, representing the close front unrounded vowel, . Originally denoting the voiceless glottal fricative, , in most dialects of Ancient Greek, it ...

) is the coefficient of efficiency (a unitless, scalar coefficient, ranging from 0 for completely inefficient to 1 for completely efficient). *

\rho

(

rho Rho (; uppercase Ρ, lowercase ρ or ; or ) is the seventeenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 100. It is derived from Phoenician alphabet, Phoenician letter resh . Its uppercase form uses the same ...

) is the

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

of water (~1000 kg/ m³) *

\dot

is the

volumetric flow rate In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol (sometimes \do ...

(in m³/s) *

\dot

is the

mass flow rate In physics and engineering, mass flow rate is the Temporal rate, rate at which mass of a substance changes over time. Its unit of measurement, unit is kilogram per second (kg/s) in SI units, and Slug (unit), slug per second or pound (mass), pou ...

(in kg/s) *

\Delta h

(

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

h) is the change in height (in

meter The metre (or meter in US spelling; symbol: m) is the base unit of length in the International System of Units (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of of ...

s) *

g

is acceleration due to gravity (9.8 m/s²) Efficiency is often higher (that is, closer to 1) with larger and more modern turbines. Annual electric energy production depends on the available water supply. In some installations, the water flow rate can vary by a factor of 10:1 over the course of a year.

Properties

Advantages

Flexibility

Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands. Hydro turbines have a start-up time of the order of a few minutes. Although battery power is quicker its capacity is tiny compared to hydro. It takes less than 10 minutes to bring most hydro units from cold start-up to full load; this is quicker than nuclear and almost all fossil fuel power. Power generation can also be decreased quickly when there is a surplus power generation. Hence the limited capacity of hydropower units is not generally used to produce base power except for vacating the flood pool or meeting downstream needs. Instead, it can serve as backup for non-hydro generators.

High value power

The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost for dispatch later as high value clean electricity. In 2021, the IEA estimated that the "reservoirs of all existing conventional hydropower plants combined can store a total of 1,500 terawatt-hours (TWh) of electrical energy in one full cycle" which was "about 170 times more energy than the global fleet of pumped storage hydropower plants". Battery storage capacity is not expected to overtake pumped storage during the 2020s. When used as

peak power ''Peak power'' refers to the maximum of the instantaneous power waveform, which, for a sine wave, is always twice the average power. For other waveforms, the relationship between peak power and average power is the peak-to-average power ratio (PAP ...

to meet demand, hydroelectricity has a higher value than

baseload power The base load (also baseload) is the minimum level of demand on an electrical grid over a span of time, for example, one week. This demand can be met by unvarying power plants or dispatchable generation, depending on which approach has the best mi ...

and a much higher value compared to

intermittent energy source Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...

s such as wind and solar. Hydroelectric stations have long economic lives, with some plants still in service after 50–100 years. Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation. Where a dam serves multiple purposes, a hydroelectric station may be added with relatively low construction cost, providing a useful revenue stream to offset the costs of dam operation. It has been calculated that the sale of electricity from the

will cover the construction costs after 5 to 8 years of full generation. However, some data shows that in most countries large hydropower dams will be too costly and take too long to build to deliver a positive risk adjusted return, unless appropriate risk management measures are put in place.

Suitability for industrial applications

While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

electrolytic plants, for example. The

switched to support

Alcoa Alcoa Corporation (an acronym for "Aluminum Company of America") is an American industrial corporation. It is the world's eighth-largest producer of aluminum. Alcoa conducts operations in 10 countries. Alcoa is a major producer of primary alu ...

aluminium in

Bellingham, Washington Bellingham ( ) is the county seat of Whatcom County, Washington, Whatcom County in the U.S. state of Washington (state), Washington. It lies south of the Canada–United States border, U.S.–Canada border, between Vancouver, British Columbia, ...

, United States for American

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In

Suriname Suriname, officially the Republic of Suriname, is a country in northern South America, also considered as part of the Caribbean and the West Indies. It is a developing country with a Human Development Index, high level of human development; i ...

, the

Brokopondo Reservoir The Brokopondo Reservoir, officially named Professor Doctor Ingenieur W. J. van Blommestein Meer, and also called the Brokopondostuwmeer, is a large reservoir in Suriname. It is named after the Surakarta-born Dutch hydrological engineer . With a ...

was constructed to provide electricity for the

aluminium industry.

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

Manapouri Power Station Manapouri is a small town in Southland, New Zealand, Southland / Fiordland, in the southwest corner of the South Island, in New Zealand. The township is the Extreme points of New Zealand#Westernmost settlements, westernmost municipality in Ne ...

was constructed to supply electricity to the

smelter Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron, copper, silver, tin, lead and zin ...

at Tiwai Point.

Reduced CO₂ emissions

Since hydroelectric dams do not use fuel, power generation does not produce

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. While carbon dioxide is initially produced during construction of the project, and some methane is given off annually by reservoirs, hydro has one of the lowest lifecycle greenhouse gas emissions for electricity generation. The low

impact of hydroelectricity is found especially in

temperate climate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ra ...

s. Greater greenhouse gas emission impacts are found in the tropical regions because the reservoirs of power stations in tropical regions produce a larger amount of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

than those in temperate areas. Like other non-fossil fuel sources, hydropower also has no emissions of sulfur dioxide, nitrogen oxides, or other particulates.

Other uses of the reservoir

Reservoirs created by hydroelectric schemes often provide facilities for

water sports Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known living organisms ...

, and become tourist attractions themselves. In some countries,

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

in reservoirs is common. Multi-use dams installed for

support

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. Managing dams which are also used for other purposes, such as

, is complicated.

Disadvantages

In 2021 the IEA called for "robust sustainability standards for all hydropower development with streamlined rules and regulations".

Ecosystem damage and loss of land

Large reservoirs associated with traditional hydroelectric power stations result in submersion of extensive areas upstream of the dams, sometimes destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife. The loss of land is often exacerbated by

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...

of surrounding areas caused by the reservoir. Hydroelectric projects can be disruptive to surrounding aquatic

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

s both upstream and downstream of the plant site. Generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. The turbines also will kill large portions of the fauna passing through, for instance 70% of the eel passing a turbine will perish immediately. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.

Drought and water loss by evaporation

Drought and seasonal changes in rainfall can severely limit hydropower. Water may also be lost by evaporation.

Siltation and flow shortage

When water flows it has the ability to transport particles heavier than itself downstream. This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation.

Siltation Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary o ...

can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam. Eventually, some reservoirs can become full of sediment and useless or over-top during a flood and fail. Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Lower river flows will reduce the amount of live storage in a reservoir therefore reducing the amount of water that can be used for hydroelectricity. The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power. The risk of flow shortage may increase as a result of

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

.Frauke Urban and Tom Mitchell 2011
Climate change, disasters and electricity generation
. London:

Overseas Development Institute ODI Global (formerly Overseas Development Institute) is a global affairs think tank, founded in 1960. Its mission is "to inspire people to act on injustice and inequality through collaborative research and ideas that matter for people and the ...

and

Institute of Development Studies An institute is an organizational body created for a certain purpose. They are often research organisations (research institutes) created to do research on specific topics, or can also be a professional body. In some countries, institutes ca ...

One study from the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-off by up to 40%.

in particular is vulnerable due to its heavy reliance on hydroelectricity, as increasing temperatures, lower water flow and alterations in the rainfall regime, could reduce total energy production by 7% annually by the end of the century.

Methane emissions (from reservoirs)

Lower positive impacts are found in the tropical regions. In lowland

areas, where inundation of a part of the forest is necessary, it has been noted that the reservoirs of power plants produce substantial amounts of

. This is due to plant material in flooded areas decaying in an

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

environment and forming methane, a

. According to the

World Commission on Dams The World Commission on Dams (WCD) existed between April 1997 and 2001, to research the environmental, social and economic impacts of the development of large dam, dams globally. The self-styled WCD consisted of members of civil society, academia ...

report, where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant. In

boreal Boreal, northern, of the north. Derived from the name of the god of the north wind from Ancient Greek civilisation, Boreas (god), Boreas. It may also refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernand ...

reservoirs of Canada and Northern Europe, however,

greenhouse gas emissions Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide (), from burning fossil fuels such as coal, petroleum, oil, and natural gas, is the main cause of climate chan ...

are typically only 2% to 8% of any kind of conventional fossil-fuel thermal generation. A new class of underwater logging operation that targets drowned forests can mitigate the effect of forest decay.

Relocation

Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In 2000, the World Commission on Dams estimated that dams had physically displaced 40–80 million people worldwide.

Failure risks

Because large conventional dammed-hydro facilities hold back large volumes of water, a failure due to poor construction, natural disasters or sabotage can be catastrophic to downriver settlements and infrastructure. During Typhoon Nina in 1975

Banqiao Dam The Banqiao Reservoir Dam () is a dam on the River Ru (), a tributary of the Hong River in Zhumadian City, Henan province, China. The Banqiao dam and Shimantan Reservoir Dam () are among 62 dams in Zhumadian that failed catastrophically in 1975 ...

in Southern China failed when more than a year's worth of rain fell within 24 hours (see

1975 Banqiao Dam failure In August 1975, the Banqiao Dam and 61 others throughout Henan, China, collapsed following the landfall of Typhoon Nina (1975), Typhoon Nina. The dam collapse created the List of natural disasters by death toll#Floods, third-deadliest flood in hi ...

). The resulting flood resulted in the deaths of 26,000 people, and another 145,000 from epidemics. Millions were left homeless. The creation of a dam in a geologically inappropriate location may cause disasters such as 1963 disaster at

Vajont Dam The Vajont Dam or Vaiont Dam is a disused hydro-electric dam in northern Italy. It is one of the tallest dams in the world, with a height of . It is in the valley of the Vajont (river) under Monte Toc, in the municipality of Erto e Casso, ...

in Italy, where almost 2,000 people died.References may be found in the list of

Dam failure A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than ...

s. The

Malpasset Dam The Malpasset Dam was an arch dam (convex surface facing upstream) on the Reyran, Reyran River, north of Fréjus on the French Riviera. It collapsed on 2 December 1959, killing 423 people in the resulting flood. The breach was caused by a tectoni ...

failure in

Fréjus Fréjus (; ) is a Communes of France, commune in the Var (department), Var Departments of France, department in the Provence-Alpes-Côte d'Azur Regions of France, region in Southeastern France. It neighbours Saint-Raphaël, Var, Saint-Raphaël ...

on the

French Riviera The French Riviera, known in French as the (; , ; ), is the Mediterranean coastline of the southeast corner of France. There is no official boundary, but it is considered to be the coastal area of the Alpes-Maritimes department, extending fr ...

(Côte d'Azur), southern France, collapsed on December 2, 1959, killing 423 people in the resulting flood. Smaller dams and

micro hydro Micro hydro is a type of hydroelectric power that typically produces from 5 kW to 100 kW of electricity using the natural flow of water. Installations below 5 kW are called pico hydro. These installations can provide power to an ...

facilities create less risk, but can form continuing hazards even after being decommissioned. For example, the small earthen embankment Kelly Barnes Dam failed in 1977, twenty years after its power station was decommissioned, causing 39 deaths.Toccoa Flood
USGS Historical Site, retrieved 02sep2009

Comparison and interactions with other methods of power generation

Hydroelectricity eliminates the flue gas emissions from fossil fuel combustion, including pollutants such as

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...

nitric oxide Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

, dust, and mercury in the

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

. Hydroelectricity also avoids the hazards of

coal mining Coal mining is the process of resource extraction, extracting coal from the ground or from a mine. Coal is valued for its Energy value of coal, energy content and since the 1880s has been widely used to Electricity generation, generate electr ...

and the indirect health effects of coal emissions. In 2021 the IEA said that government

energy policy Energy policies are the government's strategies and decisions regarding the Energy production, production, Energy distribution, distribution, and World energy supply and consumption, consumption of energy within a specific jurisdiction. Energy ...

should "price in the value of the multiple public benefits provided by hydropower plants".

Nuclear power

Nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by ...

is relatively inflexible; although it can reduce its output reasonably quickly. Since the cost of nuclear power is dominated by its high infrastructure costs, the cost per unit energy goes up significantly with low production. Because of this, nuclear power is mostly used for

baseload The base load (also baseload) is the minimum level of demand on an electrical grid over a span of time, for example, one week. This demand can be met by unvarying power plants or dispatchable generation, depending on which approach has the best mi ...

. By way of contrast, hydroelectricity can supply peak power at much lower cost. Hydroelectricity is thus often used to complement nuclear or other sources for load following. Country examples where they are paired in a close to 50/50 share include the electric grid in Switzerland, the

Electricity sector in Sweden Majority of electricity production in Sweden relies on hydro power and nuclear power. In 2008 the consumption of electricity in Sweden was per capita, compared to EU average per capita.Ukraine Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...

and the Electricity sector in Finland.

Wind power

Wind power Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity ge ...

goes through predictable variation by season, but is intermittent on a daily basis. Maximum wind generation has little relationship to peak daily electricity consumption, the wind may peak at night when power is not needed or be still during the day when electrical demand is highest. Occasionally weather patterns can result in low wind for days or weeks at a time, a hydroelectric reservoir capable of storing weeks of output is useful to balance generation on the grid. Peak wind power can be offset by minimum hydropower and minimum wind can be offset with maximum hydropower. In this way the easily regulated character of hydroelectricity is used to compensate for the intermittent nature of wind power. Conversely, in some cases wind power can be used to spare water for later use in dry seasons. An example of this is Norway's trading with Sweden, Denmark, the Netherlands, Germany and the UK. Norway is 98% hydropower, while its flatland neighbors have wind power. In areas that do not have hydropower,

pumped storage Pumping may refer to: * The operation of a pump, for moving a liquid from one location to another **The use of a breast pump A breast pump is a mechanical device that Lactation, lactating women use to milking, extract milk from their breasts. They ...

serves a similar role, but at a much higher cost and 20% lower efficiency.

Hydro power by country

In 2022, hydro generated 4,289 TWh, 15% of total electricity and half of renewables. Of the world total,

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

(30%) produced the most, followed by

(10%),

(9.2%), the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

(5.8%) and

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

(4.6%). Paraguay produces nearly all of its electricity from hydro and exports far more than it uses. Larger plants tend to be built and operated by national governments, so most capacity (70%) is publicly owned, despite the fact that most plants (nearly 70%) are owned and operated by the private sector, as of 2021. The following table lists these data for each country: * total generation from hydro in

terawatt-hours A kilowatt-hour ( unit symbol: kW⋅h or kW h; commonly written as kWh) is a non-SI unit of energy equal to 3.6 megajoules (MJ) in SI units, which is the energy delivered by one kilowatt of power for one hour. Kilowatt-hours are a commo ...

, * percent of that country's generation that was

hydro Hydro (from ) may refer to: Energy technologies * Water-derived power or energy: ** Hydropower, derived from water ** Hydroelectricity, in electrical form * "Hydro", AC mains electricity in parts of Canada * Micro hydro, a type of hydroelect ...

, * total hydro capacity in

gigawatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named in honor o ...

, * percent growth in hydro capacity, and * the hydro

for that year. Data are sourced from

Ember An ember, also called a hot coal, is a hot lump of smouldering solid fuel, typically glowing, composed of greatly heated wood, coal, or other carbon-based material. Embers (hot coals) can exist within, remain after, or sometimes precede, a ...

dating to the year 2023 unless otherwise specified. Only includes countries with more than 1 TWh of generation. Links for each location go to the relevant hydro power page, when available.

Economics

The

weighted average cost of capital The weighted average cost of capital (WACC) is the rate that a company is expected to pay on average to all its security holders to finance its assets. The WACC is commonly referred to as the firm's cost of capital. Importantly, it is dictated by ...

is a major factor.

References

Sources

External links

Hydropower Reform Coalition
*
European Small Hydropower AssociationIEC TC 4: Hydraulic turbines
(International Electrotechnical Commission - Technical Committee 4) IEC TC 4 portal with access to scope, documents an

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