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Hydroelectricity, or hydroelectric power, is electricity produced from
hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and th ...
. In 2015, hydropower generated 16.6% of the world's total electricity and 70% of all
renewable electricity Renewable energy is useful energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the portio ...
, and was expected to increase by about 3.1% each year for the next 25 years. Hydropower is produced in 150 countries, with the
Asia-Pacific The Asia-Pacific is the part of the world In its most general sense, the term "world" refers to the totality of entities, to the whole of reality or to everything that is. The nature of the world has been conceptualized differently in dif ...

Asia-Pacific
region generating 33 percent of global hydropower in 2013.
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...

China
is the largest hydroelectricity producer, with of production in 2013, representing 16.9% of domestic electricity use. The cost of hydroelectricity is relatively low, making it a competitive source of renewable electricity. The hydro station consumes no water, unlike coal or gas plants. The typical cost of electricity from a hydro station larger than 10
megawatt The watt (symbol: W) is a unit of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equa ...
s is 3 to 5
US cent The United States one-cent coin (symbol: ¢), often called the penny, is a unit of currency A currency, "in circulation", from la, currens, -entis, literally meaning "running" or "traversing" in the most specific sense is money Image:N ...
s per
kilowatt hour The kilowatt-hour ( SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fictio ...
. With a dam and reservoir it is also a flexible source of electricity, since the amount produced by the station can be varied up or down very rapidly (as little as a few seconds) to adapt to changing energy demands. Once a hydroelectric complex is constructed, the project produces no direct waste, and it generally has a considerably lower output level of
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhou ...
es than photovoltaic power plants and certainly
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
powered energy plants (see also
Life-cycle greenhouse-gas emissions of energy sources Measurement of life-cycle greenhouse gas emissions involves calculating the global-warming potential of energy sources through life-cycle assessment Life-cycle assessment or LCA (also known as life-cycle analysis) is a methodology for asses ...
).Renewables 2011 Global Status Report, page 25, Hydropower
''
REN21 REN21 (Renewable Energy Policy Network for the 21st Century) is a think tank A think tank, or policy institute, is a research institute A research institute, research centre, or research center is an establishment founded for doing research ...
'', published 2011, accessed 2016-02-19.
However, when constructed in lowland
rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapevine Religi ...

rainforest
areas, where inundation of a part of the forest is necessary, they can emit substantial amounts of greenhouse gases. The construction of a hydroelectric complex can cause significant environmental impact, principally in loss of arable land and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and the siltation and erosion patterns. While dams can ameliorate the risks of flooding, they also contain a risk of
dam failure A dam failure or dam burst is a catastrophic type of 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 200 notable ...
, which can be catastrophic.


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 was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
. In the mid-1770s, French engineer
Bernard Forest de Bélidor Bernard Forest de Bélidor (1698, Catalonia Catalonia (; ca, Catalunya ; Aranese, Aranese Occitan: ''Catalonha'' ; es, Cataluña ) is an Autonomous communities of Spain, autonomous community in the northeastern corner of Spain, designated as ...
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 The Industrial Revolution was the transition to new manufacturing processes in Great ...

Richard Arkwright
’s combination of
water power Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and th ...

water power
, the
water frame #REDIRECT Water frame#REDIRECT Water frame upModel of a water frame in the Museum for Early Industrialisation in Wuppertal. The water frame is a spinning frame that is powered by a water-wheel. Water frames in general have existed since Ancient ...
, and
continuous production Continuous production is a flow production method used to manufacturing, manufacture, produce, or process materials without interruption. Continuous production is called a continuous process or a continuous flow process because the materials, eit ...
played a significant part in the development of the factory system, with modern employment practices. In the 1840s the
hydraulic power network A hydraulic power network is a system of interconnected pipes carrying pressurized {{Wiktionary Pressurization or pressurisation is the application of pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics ( ...
was developed to generate and transmit hydro power to end users. By the late 19th century, the
electrical generator In electricity generation Electricity generation is the process of generating electric power from sources of primary energy. For electric utility, utilities in the electric power industry, it is the stage prior to its Electricity delivery, deliv ...
was developed and could now be coupled with hydraulics. The growing demand arising from the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe Continental Europe or mainland Europe is the contiguous continent A continent is any of several large landmasse ...
would drive development as well. In 1878, the world's first hydroelectric power scheme was developed at
Cragside Cragside is a Victorian era, Victorian 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 armaments firm. An industrial magnate, scien ...

Cragside
in
Northumberland Northumberland () is a ceremonial county The counties and areas for the purposes of the lieutenancies, also referred to as the lieutenancy areas of England and informally known as ceremonial counties, are areas of England to which lord-li ...

Northumberland
, 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 An electric arc, or arc discharge, is an of a that produces a prolonged . The through a normally medium such as produces a ; the plasma may produce . An arc discha ...
in his art gallery. The old , 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 U.S. state, state o ...

Niagara Falls
, began to produce electricity in 1881. The first hydroelectric power station, the
Vulcan Street Plant The Vulcan Street Plant was the first Edison hydroelectric central station.Appleton, Wisconsin Appleton is a city in Outagamie, Calumet Calumet may refer to: Places United States *Calumet Region, in northern Illinois and Indiana **Calumet River **Calumet Trail, Indiana **Calumet (East Chicago) *Calumet, Colorado *Calumet, Iowa *Calumet ...
, 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 ( , ; , ''Grainóvol'', oc, Graçanòbol, ''Grasanòbol'') is the prefecture A prefecture (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. ...

Grenoble
, France held the
International Exhibition of Hydropower and Tourism The International Exhibition of Hydropower and Tourism (French: ''Exposition internationale de la houille blanche et du tourisme'') was an exhibition which ran from May 21 to October 25, 1925 in the city of Grenoble Grenoble ( , ; ) is the Prefe ...
, with over one million visitors. By 1920, when 40% of the power produced in the United States was hydroelectric, the
Federal Power ActThe 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 origina ...
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 control methods are used to reduce or prevent the detrimental effects of flood A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the ...
,
irrigation Irrigation is the agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in seden ...

irrigation
and
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
. 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 Federal government of the United States, federally-owned electric utility corporation in the United States. TVA's service area covers all of Tennessee, portions of Alabama, Mississippi, and Kentucky, a ...
(1933) and the
Bonneville Power Administration The Bonneville Power Administration (BPA) is an American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of America (USA), commo ...
(1937) were created. Additionally, the
Bureau of Reclamation The United States Bureau of Reclamation (USBR), and formerly the United States Reclamation Service, is a federal agency under the U.S. Department of the Interior, which oversees water resource management, specifically as it applies to the ...
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 Hoover Dam is a in the of the , on the border between the U.S. states of and . It was constructed between 1931 and 1936 during the and was dedicated on September 30, 1935, by President . Its construction was the result of a massive ef ...
. The
United States Army Corps of Engineers , colors = , battles = , battles_label = Wars , website = , commander1 = LTG Scott A. Spellmon , commander1_label = Comma ...
was also involved in hydroelectric development, completing the
Bonneville Dam Bonneville Lock and Dam consists of several Run-of-the-river hydroelectricity, run-of-the-river dam structures that together complete a span of the Columbia River between the U.S. states of Oregon and Washington (state), Washington at River Mile ...
in 1937 and being recognized by the
Flood Control Act of 1936 The Flood Control Act of 1936, , (FCA 1936) was an Act of the United States Congress signed into law by President Franklin Delano Roosevelt Franklin Delano Roosevelt (, ; January 30, 1882April 12, 1945), often referred to by his initial ...
as the premier federal flood control agency.The Evolution of the Flood Control Act of 1936, Joseph L. Arnold
United States Army Corps of Engineers , colors = , battles = , battles_label = Wars , website = , commander1 = LTG Scott A. Spellmon , commander1_label = Comma ...
, 1988
Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as ''white coal''.
Hoover Dam Hoover Dam is a in the of the , on the border between the U.S. states of and . It was constructed between 1931 and 1936 during the and was dedicated on September 30, 1935, by President . Its construction was the result of a massive ef ...

Hoover Dam
'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 The Columbia River (Upper Chinook language, Upper Chinook: ' or '; Sahaptin language, Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river ...

Grand Coulee Dam
in 1942. The
Itaipu Dam The Itaipu Dam ( pt, Barragem de Itaipu , es, Represa de Itaipú ) is a hydroelectric dam Hydroelectricity, or hydroelectric power, is electricity produced from hydropower. In 2015, hydropower generated 16.6% of the world's total electr ...

Itaipu Dam
opened in 1984 in South America as the largest, producing , but was surpassed in 2008 by the
Three Gorges Dam The Three Gorges Dam is a that spans the by the town of , in , , province, central , downstream of the . The Three Gorges Dam has been the in terms of (22,500 ) since 2012. The dam generates an average 95±20 TWh of electricity per ...

Three Gorges Dam
in China at . Hydroelectricity would eventually supply some countries, including
Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language Norwegian (Norwegian: ''norsk'') is a Nort ...

Norway
,
Democratic Republic of the Congo The Democratic Republic of the Congo ( french: République démocratique du Congo (RDC) ), also known as Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly Zaire Zaire (, ), officially the Republic of Zaire (frenc ...

Democratic Republic of the Congo
,
Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tetã Paraguái, links=no), is a country in South America South America is a entirely in the and mostly in the , with a relatively sma ...

Paraguay
and
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
, with over 85% of their electricity. The United States currently has over 2,000 hydroelectric power stations that supply 6.4% of its total electrical production output, which is 49% of its renewable electricity.


Future potential

The technical potential for hydropower development around the world is much greater than the actual production: the percent of potential hydropower capacity that has not been developed is 71% in Europe, 75% in North America, 79% in South America, 95% in Africa, 95% in the Middle East, and 82% in Asia-Pacific. Due to the political realities of new reservoirs in western countries, economic limitations in the third world and the lack of a transmission system in undeveloped areas, perhaps 25% of the remaining technically exploitable potential can be developed before 2050, with the bulk of that being in the Asia-Pacific area. Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%.


Generating methods


Conventional (dams)

Most hydroelectric power comes from the
potential energy In physics, potential energy is the energy In , energy is the that must be to a or to perform on the body, or to it. Energy is a ; the law of states that energy can be in form, but not created or destroyed. The unit of measure ...

potential energy
of
dam A dam is a barrier that stops or restricts the flow of surface water An example of surface water is Lake Kinney. Surface water is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tas ...

dam
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, the ...

water turbine
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 Head Sport GmbH is an American-Austrian manufacturing company Manufacturing is the creation or production Production may be: Economics and business * Production (economics) * Production, the act of manufacturing goods * Production, in th ...
. A large pipe (the "
penstock A penstock is a sluice or floodgate, gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydro turbines and sanitary sewer, sewerage systems. The term is inherited from the earlier technology of mill ...
") delivers water from the
reservoir A reservoir (; from French ''réservoir'' ) is most commonly an enlarged natural or artificial lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not per ...

reservoir
to the turbine.


Pumped-storage

This method produces electricity to supply high peak demands by moving water between
reservoir A reservoir (; from French ''réservoir'' ) is most commonly an enlarged natural or artificial lake A lake is an area filled with water, localized in a basin, surrounded by land Land is the solid surface of Earth that is not per ...

reservoir
s at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir. When the demand becomes greater, water is released back into the lower reservoir through a turbine. Pumped-storage schemes currently provide the most commercially important means of large-scale
grid energy storage Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage Energy storage is the capture of energy In physics, energy is the physical quantity, quantitative physical property, prop ...
and improve the daily
capacity factor The net capacity factor is the unitless ratio of an actual electrical energy output over a given period of time to the maximum possible electrical energy output over that period. The capacity factor is defined for any electricity producing install ...
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. In the United States, run of the river hydropower could potentially provide (about 13.7% of total use in 2011 if continuously available).


Tide

A
tidal power#REDIRECT Tidal power Tidal power or tidal energy is harnessed by converting energy from tide (U.S.), low tide occurs roughly at moonrise and high tide with a high Moon, corresponding to the simple gravity model of two tidal bulges; at most ...
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 Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
or undammed sources such as undershot
water wheel The reversible water wheel powering a mine hoist in ''De re metallica'' (Georgius Agricola">De_re_metallica.html" ;"title="mine hoist in ''De re metallica">mine hoist in ''De re metallica'' (Georgius Agricola, 1566) A water wheel is a machi ...

water wheel
s. Tidal power is viable in a relatively small number of locations around the world. In Great Britain, there are eight sites that could be developed, which have the potential to generate 20% of the electricity used in 2012.


Sizes, types and capacities of hydroelectric facilities


Large facilities

Large-scale hydroelectric power stations are more commonly seen as the largest power producing facilities in the world, 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 a unit of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equa ...
s are generally considered large hydroelectric facilities. Currently, only four facilities over () are in operation worldwide, see table below.


Small

Small hydro is the development of
hydroelectric power Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machin ...
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
megawatt The watt (symbol: W) is a unit of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equa ...
s (MW) is generally accepted as the upper limit of what can be termed small hydro. This may be stretched to and in
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

Canada
and the United States. Small-scale hydroelectricity production grew by 29% from 2005 to 2008, raising the total world small-hydro capacity to . Over 70% of this was in
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...

China
(), followed by
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
(), the United States (), and
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
(). 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 network, 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 is a term used for
hydroelectric power Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machin ...
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 commercia ...
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 a term used for
hydroelectric power Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machin ...
generation of under . It is useful in small, remote communities that require only a small amount of electricity. For example, the 1.1 kW ITDG Pico Hydro Project in Kenya supplies 57 homes with very small electric loads (e.g., a couple of lights and a phone changer, 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, 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

An
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 more ...
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.


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 is
power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, p ...
(in
watt The watt (symbol: W) is a unit of power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equa ...

watt
s) * \eta (
eta Eta (uppercase , lowercase ; grc, ἦτα ''ē̂ta'' or ell, ήτα ''ita'' ) is the seventh letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is ...
) 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 ; el, ῥῶ) is the 17th letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is derived from the earlier Phoenician ...
) is the
density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its per unit . The symbol most often used for density is ''ρ'' (the lower case Greek letter ), although the Latin letter ''D'' can also ...

density
of water (~1000  kg/ m3) * \dot is the
volumetric flow rate In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...
(in m3/s) * \dot is the
mass flow rate In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit of measurement, unit is kilogram per second in SI units, and Slug (unit), slug per second or pound (mass), pound per second in US custo ...
(in kg/s) * \Delta h (
Delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, a landform at the mouth of a river * D (NATO phonetic alphabet: "Delta"), the fourth letter of the modern English alphabet * Delta Air Lines, an Ame ...
h) is the change in height (in
meter The metre ( Commonwealth spelling) or meter (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English ...

meter
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. It takes around 60 to 90 seconds to bring a unit from cold start-up to full load; this is much shorter than for gas turbines or steam plants. 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.


Low cost/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. The average cost of electricity from a hydro station larger than 10 megawatts is 3 to 5 US cents per kilowatt-hour. When used as peak power to meet demand, hydroelectricity has a higher value than base power and a much higher value compared to
intermittent energy source Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, a ...
s. 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
Three Gorges Dam The Three Gorges Dam is a that spans the by the town of , in , , province, central , downstream of the . The Three Gorges Dam has been the in terms of (22,500 ) since 2012. The dam generates an average 95±20 TWh of electricity per ...

Three Gorges Dam
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 (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
electrolytic plants, for example. The
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Grand Coulee Dam
switched to support
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airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In
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, the
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Brokopondo Reservoir
was constructed to provide electricity for the
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aluminium industry.
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's
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Manapouri Power Station
was constructed to supply electricity to the
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.


Reduced CO2 emissions

Since hydroelectric dams do not use fuel, power generation does not produce
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
. 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. Compared to fossil fuels generating an equivalent amount of electricity, hydro displaced three billion tonnes of CO2 emissions in 2011. According to a comparative study by the
Paul Scherrer Institute The Paul Scherrer Institute (PSI) is a multi-disciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic disciplines into one activity (e.g., a research project). It draws knowledge from se ...
and the
University of Stuttgart The University of Stuttgart (german: Universität Stuttgart) is a leading research university A research university is a university A university ( la, universitas, 'a whole') is an educational institution, institution of higher education, high ...

University of Stuttgart
, hydroelectricity in Europe produces the least amount of
greenhouse gases A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature' ...

greenhouse gases
and
externality In economics Economics () is the social science that studies how people interact with value; in particular, the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods ...

externality
of any energy source. Coming in second place was
wind Wind is the natural movement of air or other gases relative to a planet's surface. Wind occurs on a range of scales, from thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by th ...
, third was
nuclear energy Nuclear energy may refer to: *Nuclear power, the use of sustained nuclear fission or nuclear fusion to generate heat and electricity *Nuclear binding energy, the energy required to split a nucleus of an atom *Nuclear potential energy, the potential ...

nuclear energy
, and fourth was
solar Solar may refer to: Astronomy * Of or relating to the Sun. ** A solar telescope 175px, The Swedish 1-m Solar Telescope at Roque de los Muchachos Observatory, La Palma in the Canary Islands. A solar telescope is a special purpose telescope used ...

solar
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 commercia ...

photovoltaic
. The low
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhou ...
impact of hydroelectricity is found especially in
temperate climate In geography Geography (from Ancient Greek, Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and Solar System, plan ...
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 A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
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 (chemical formula H2O) is an inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, struc ...
, and become tourist attractions themselves. In some countries,
aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the farming of fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct rel ...
in reservoirs is common. Multi-use dams installed for
irrigation Irrigation is the agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in seden ...

irrigation
support
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project.


Disadvantages


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 Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biop ...
of surrounding areas caused by the reservoir. Hydroelectric projects can be disruptive to surrounding aquatic
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

ecosystem
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. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.


Water loss by evaporation

A 2011 study by the
National Renewable Energy Laboratory The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development Research and development (R&D, R+D), known in Europe as research and technological development (RTD), is the set of innovative activi ...

National Renewable Energy Laboratory
concluded that hydroelectric plants in the United States consumed between of electricity generated, through evaporation losses in the reservoir. The median loss was , which is higher than the loss for generation technologies that use cooling towers, including concentrating solar power at for CSP trough and for CSP tower, coal at , nuclear at , and natural gas at . Where there are multiple uses of reservoirs such as water supply, recreation, and flood control, all reservoir evaporation is attributed to power production.


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 Water pollution (or aquatic pollution) is the contamination of water bodies ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Kingdom of Norway, is ...
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 Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
.Frauke Urban and Tom Mitchell 2011
Climate change, disasters and electricity generation
. London:
Overseas Development Institute The Overseas Development Institute (ODI) is a global affairs think tank, founded in 1960. Formally known as the “Overseas Development Institute”, its mission is "to inspire people to act on injustice and inequality through collaborative res ...
and
Institute of Development Studies The Institute of Development Studies (IDS) is a think tank A think tank, or policy institute, is a research institute A research institute, research centre, or research center is an establishment founded for doing research. Research instit ...
One study from the
Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid drainage basin, watershed that encompasses parts of ...

Colorado River
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%.
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
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
rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapevine Religi ...

rainforest
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
methane Methane (, ) is a chemical compound with the chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes a ...
. 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
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhou ...
. 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, meaning "(far) northern" in Latin and Greek language, Greek, may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a c ...
reservoirs of Canada and Northern Europe, however,
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without ...
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 Sunset over Hong River, view from Long Bien Bridge, Hanoi, Vietnam The Hong River (; vi, Sông Hồng), also known as the Red River, the ' and ' (lit. ...
in Southern China failed when more than a year's worth of rain fell within 24 hours (see
1975 Banqiao Dam failure The 1975 Banqiao Dam failure (simplified Chinese Simplification, Simplify, or Simplified may refer to: Mathematics Simplification is the process of replacing a mathematical expression by an equivalent one, that is simpler (usually shorter), for ...
). 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 dam in northern Italy. It is one of the , with a height of . It is situated in the valley of the Vajont River under , in the municipality of , north of . The dam was conceived in the 1920s and even ...

Vajont Dam
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 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 200 notable ...
s.
The
Malpasset Dam The Malpasset Dam () was an arch dam An arch dam is a concrete dam that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, causing the arch ...
failure in
Fréjus Fréjus (; , ) is a commune A commune is an intentional community of people sharing living spaces, interests, values, beliefs, and often property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs ...
on the
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French Riviera
(Côte d'Azur), southern France, collapsed on December 2, 1959, killing 423 people in the resulting flood. Smaller dams and
micro hydro Micro may refer to: Measurement * micro- (μ), a prefix in the SI and other systems of units denoting a factor of 10−6 (one millionth) Places * Micro, North Carolina, town in U.S. People * DJ Micro, (born Michael Marsicano) an American trance ...
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, nitric oxide, carbon monoxide, dust, and mercury (element), mercury in the coal. Hydroelectricity also avoids the hazards of coal mining and the indirect health effects of coal emissions.


Nuclear power

Compared to nuclear power, hydroelectricity construction requires altering large areas of the environment while a nuclear power station has a small footprint, and hydro-powerstation failures have caused tens of thousands of more deaths than any nuclear station failure. The creation of Garrison Dam, for example, required Native American land to create Lake Sakakawea, which has a shoreline of , and caused the inhabitants to sell 94% of their arable land for $7.5 million in 1949. However, nuclear power is relatively inflexible; although nuclear power 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. 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 Electricity sector in Switzerland, the electric grid in Switzerland, the Electricity sector in Sweden and to a lesser extent, Energy in Ukraine#Electricity, Ukraine and the Electricity sector in Finland.


Wind power

Wind power goes through predictable Variable renewable energy, variation by season, but is Intermittent energy source, intermittent on a daily basis. Maximum wind generation has little relationship to peak daily electricity consumption, the wind may peak at night when power isn't 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. In areas that do not have hydropower, pumped storage serves a similar role, but at a much higher cost and 20% lower efficiency. An example of this is Electricity sector in Norway, Norway's trading with Sweden, Denmark, the Netherlands and possibly Germany or the United Kingdom, UK in the future. Norway is 98% hydropower, while its flatland neighbors are installing wind power.


World hydroelectric capacity

The ranking of hydroelectric capacity is either by actual annual energy production or by installed capacity power rating. In 2015 hydropower generated 16.6% of the worlds total electricity and 70% of all renewable electricity. Hydropower is produced in 150 countries, with the Asia-Pacific region generated 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use.
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
,
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

Canada
,
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
,
Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language Norwegian (Norwegian: ''norsk'') is a Nort ...

Norway
,
Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tetã Paraguái, links=no), is a country in South America South America is a entirely in the and mostly in the , with a relatively sma ...

Paraguay
, Austria, Switzerland, Venezuela, and several other countries have a majority of the internal electric energy production from hydroelectric power.
Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tetã Paraguái, links=no), is a country in South America South America is a entirely in the and mostly in the , with a relatively sma ...

Paraguay
produces 100% of its electricity from hydroelectric dams and exports 90% of its production to Brazil and to Argentina.
Norway Norway, officially the Kingdom of Norway,Names in the official and recognised languages: Bokmål Bokmål (, ; literally "book tongue") is an official written standard for the Norwegian language Norwegian (Norwegian: ''norsk'') is a Nort ...

Norway
produces 96% of its electricity from hydroelectric sources. A hydroelectric station rarely operates at its full power rating over a full year; the ratio between annual average power and installed capacity rating is the
capacity factor The net capacity factor is the unitless ratio of an actual electrical energy output over a given period of time to the maximum possible electrical energy output over that period. The capacity factor is defined for any electricity producing install ...
. The installed capacity is the sum of all generator nameplate power ratings.Consumption BP.com
/ref>


See also

* Hydraulic engineering * International Rivers * List of energy storage projects * List of hydroelectric power station failures * List of largest power stations * List of renewable energy topics by country * Lists of hydroelectric power stations * Marine current power - electricity from sea currents * Renewable energy transition


References


External links


International Hydropower Association
*
National Hydropower Association
US
Hydropower Reform CoalitionInteractive demonstration on the effects of dams on riversEuropean Small Hydropower AssociationIEC TC 4: Hydraulic turbines
(International Electrotechnical Commission - Technical Committee 4) IEC TC 4 portal with access to scope, documents an

{{Authority control Bright green environmentalism Hydroelectricity, Landscape Sustainable technologies