TheInfoList

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 Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, converting the Pote ...
. 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 300px, Map showing the general definition of Asia-Pacific. Dark green refers to the core Asia-Pacific countries, while light green refers to regions that may be included. The Asia-Pacific is the part of the world The world is the Earth and ...
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. It is the List of countries and dependencies by population, world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6& ...
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, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, ...
. 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 Gas is one of the four fundamental states of matter (the others being solid, liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformat ...
es than photovoltaic power plants and certainly
fossil fuel A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous sys ...
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. Re ...
'', 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 ...

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 Mainland or continental Europe is the contiguous continent of Europe, excluding its surrounding islands. It can also be ...
. 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 Br ...

’s combination of
water power 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 machines. This is achieved by converting the water's kinetic energy In physics, the kineti ...

, the
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 Egypt 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 liquid used to transmit mechanical power Mechanical power is a medical term which is a measure of the amount of energy imparted to a patient by a mechanical ventila ...
was developed to generate and transmit hydro power to end users. By the late 19th century, the
electrical generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbine A steam turbine is a device that extra ...
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 Mainland or continental Europe is the contiguous continent of Europe, excluding its surrounding islands. It can also be ...
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, scient ...
in
Northumberland Northumberland () is a ceremonial counties of England, ceremonial county and Historic counties of England, historic county in North East England. It is bordered by Cumbria to the west, County Durham and Tyne and Wear to the south and the Scot ...

, England by William Armstrong. It was used to power a single
arc lamp . The two lamps, used for laser pumping, are very different in the shape of the electrodes, in particular, the cathode (on the left). An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbo ...
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 of ...

, 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 County, Wisconsin, Outagamie, Calumet County, Wisconsin, Calumet, and Winnebago County, Wisconsin, Winnebago counties in the U.S. state of Wisconsin. One of the Fox Cities, it is situated on the Fox River (Wisconsi ...
, 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 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 Auverg ...

, 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 waters."Flood Control", MSN Encarta, 2008 (see below: #Further reading, Further reading). Flood relief methods are used to reduce the effects of flood waters or ...
,
irrigation Irrigation is the artificial process of applying controlled amounts of water to land to assist in production of crops. Irrigation helps to grow agricultural crops, maintain landscapes, and revegetate disturbed soils in dry areas and during p ...

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, m ...
. 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 corporation A corporation is an organization—usually a group of people or a company—authorized by the state to act as a single entity (a legal entity recognized by private and ...
(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 Congress in 1937 to market electric power from the Bonneville Dam located on the Columbia River 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 concrete File:Pantheon cupola.jpg, Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, mounted on temporary scaffolding. Concrete is a composite material composed o ...
. The
United States Army Corps of Engineers , colors = , battles = , battles_label = Wars , website = , commander1 = Lt. Gen. Scott A. Spellmon , commander1_label = ...
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 = Lt. Gen. Scott A. Spellmon , commander1_label = ...
, 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 concrete File:Pantheon cupola.jpg, Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, mounted on temporary scaffolding. Concrete is a composite material composed o ...

'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 ...

in 1942. The
Itaipu Dam The Itaipu Dam ( pt, Barragem de Itaipu, es, Represa de Itaipú; , ) is a hydroelectric dam on the Paraná River located on the border between Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is ...

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 hydroelectricity, hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has ...

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, alongside Nynorsk. Bokmål is the preferred ...

,
Democratic Republic of the Congo The Democratic Republic of the Congo (DRC) ( french: République démocratique du Congo (RDC) ), also known as Congo-Kinshasa, DR Congo (french: RD Congo), the DROC, or simply either Congo or the Congo, and historically Zaire, is a country in ...
,
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 continent entirely in the Western Hemisphere and mostly in ...

and
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
, 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 held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potential ...

of
dam A dam is a barrier that stops or restricts the flow of water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, whic ...
med water driving a
water turbine A water turbine is a rotary machine that converts kinetic energy and potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge ...

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 headquartered in Kennelbach. It owns the American tennis racket brand Head. Head GmbH is a group that includes several previously independent companies, including the original "Head ...
. 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 French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République française), is a country primarily loca ...

to the turbine.

## Pumped-storage

This method produces electricity to supply high peak demands by moving water between
reservoir A reservoir (; from French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République française), is a country primarily loca ...

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 File:grid storage energy flow.png, Simplified grid energy flow with and without idealized energy storage for the course of one day Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on ...
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, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. It is defined as the work (physics), work needed to accelerate a body of a given mass from rest to its stated velocity. Having gaine ...
or undammed sources such as undershot
water wheel The reversible water wheel powering a mine hoist in ''De re metallica'' (Georgius Agricola, 1566) A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water whe ...

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. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northward into the Arctic Ocea ...

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. It is the List of countries and dependencies by population, world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6& ...
(), followed by
Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of Japan.svg , alt_coat = Golden circle subdiv ...

(), the United States (), and
India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populous country, the List of countries and dependencies by area, seventh-largest ...

(). 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: $P = -\eta \ \left(\dot g \ \Delta h\right) = -\eta \ \left(\left(\rho \dot\right) \ g \ \Delta h\right)$ 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, equal ...

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 mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...

of water (~1000  kg/ m3) * $\dot$ is the
volumetric flow rate In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through ...
(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; see spelling differences) (from the French unit , from the Greek noun , "measure", and cognate with Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, no ...

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

### 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 Grids with high penetration of renewable energy sources generally need more flexible generation rather than baseload generation Variable renewable energy (VRE) (also called intermittent renewable energy sources (IRES)) is a renewable energy ...
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 hydroelectricity, hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has ...

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 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), commonly known as the Unit ...

electrolytic plants, for example. 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 ...

switched to support
Alcoa Alcoa Corporation (a portmanteau A portmanteau (, ) or portmanteau word (from "portmanteau (luggage) A portmanteau is a piece of luggage, usually made of leather and opening into two equal parts. Some were large, upright, and hinged at the b ...
aluminium in
Bellingham, Washington Bellingham ( ) is the most populous city in and 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 in between tw ...
, United States for American
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In
Suriname Suriname (, sometimes spelled Surinam), officially known as the Republic of Suriname ( nl, Republiek Suriname ), is a country on the northeastern Atlantic coast of South America. Borders of Suriname, It is bordered by the Atlantic Ocean to the ...

, 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 (water), reservoir in Suriname. It is named after the Surakarta-born Netherlands, Dutch ...

was constructed to provide electricity for the
Alcoa Alcoa Corporation (a portmanteau A portmanteau (, ) or portmanteau word (from "portmanteau (luggage) A portmanteau is a piece of luggage, usually made of leather and opening into two equal parts. Some were large, upright, and hinged at the b ...
aluminium industry.
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and more than 700 List of islands of New Zealand, smaller islands, coveri ...

's
Manapouri Power Station Manapōuri Power Station is an underground hydroelectric 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 ...

was constructed to supply electricity to the
aluminium Aluminium (aluminum in 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), commonly known as the Unit ...

smelter Smelting is a process of applying heat to ore in order to extract a base metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, sh ...
at
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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 ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

. 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 ...

, 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' ...

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 ...

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 flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hours, ...
, 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 ...

, 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 ...

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 ...

. The low
greenhouse gas A greenhouse gas (GHG or GhG) is a gas Gas is one of the four fundamental states of matter (the others being solid, liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformat ...
impact of hydroelectricity is found especially in
temperate climate In geography Geography (from 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 planets. The first person to use ...
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 atom An atom is the smallest unit of ordinary matter In classical physics an ...
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 Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in ...
in reservoirs is common. Multi-use dams installed for
irrigation Irrigation is the artificial process of applying controlled amounts of water to land to assist in production of crops. Irrigation helps to grow agricultural crops, maintain landscapes, and revegetate disturbed soils in dry areas and during p ...

support
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentism, sedentary human civilization, whereby farming of domestication, domesticated species created food ...

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

### 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 Fragmentation and destruction of Great Ape habitat in Central Africa, from thGLOBIOand GRASP projects (2002). Areas shown in black and red delineate areas of severe and moderate habitat loss, respectively. Habitat fragmentation describes the emer ...
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 syste ...

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 activit ...

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 event ...
.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 ...

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 South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
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 ...

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 atom An atom is the smallest unit of ordinary matter In classical physics an ...
. 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 adh ...
environment and forming methane, a
greenhouse gas A greenhouse gas (GHG or GhG) is a gas Gas is one of the four fundamental states of matter (the others being solid, liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformat ...
. 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 th ...
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 tallest dams in the world, with a height of . It is situated in the valley of the Vajont River under Monte Toc, in the municipality of Erto e Casso, north of ...

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
French Riviera The French Riviera (known in French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, République française), is a country prima ...

(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 Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
,
nitric oxide Nitric oxide ( nitrogen oxide 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, i.e., it has an unpaired electron, which is sometimes denoted by a dot i ...

,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

, dust, and
mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

in the
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country located mostly in the southern half o ...

. Hydroelectricity also avoids the hazards of
coal mining in the United States , Belgium Coal mining is the process of resource extraction, extracting coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata (Argentina Argentina (), officially the Arge ...

and the indirect health effects of coal emissions.

### Nuclear power

Compared to
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 ...

, 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 Garrison Dam is an earth-fill embankment dam in Pakistan Pakistan, . Pronounced variably in English language, English as , , , and . officially the Islamic Republic of Pakistan, is a country in South Asia. It is the world's List of countr ...
, 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 The baseload (also base load) on a grid is the minimum level of demand on an electrical grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover who ...
. 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 followingA load following power plant, regarded as producing mid-merit or mid-priced electricity, is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load following plants are typically in-between base load ...
. 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 Sweden (; sv, Sverige ), officially the Kingdom of Sweden ( sv, links=no, Konungariket Sverige ), is a Nordic countries, Nordic country in Northern Europe.The United Nations Group of Experts on ...
and to a lesser extent,
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the List of European countries by area, second-largest country by area in Europe after Russia, which it borders to the east and north-east. Ukraine also shares bo ...

and the Electricity sector in Finland.

### Wind power

Wind power Wind power or wind energy is the use of wind turbine A wind turbine is a device that converts the wind's kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. ...

goes through predictable
variation Variation or Variations may refer to: Science and mathematics * Variation (astronomy), any perturbation of the mean motion or orbit of a planet or satellite, particularly of the moon * Genetic variation thumb File:Genetic Variation and Inhe ...
by season, but is
intermittent In dynamical systems, intermittency is the irregular alternation of phases of apparently periodic and Chaos theory, chaotic dynamics (Pomeau–Manneville scenario, Pomeau–Manneville dynamics), or different forms of chaotic dynamics (crisis-in ...
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 Pumping may refer to: * The operation of a pump near the Hengsteysee, GermanyA pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic ...
serves a similar role, but at a much higher cost and 20% lower efficiency. An example of this is Norway's trading with
Sweden Sweden ( sv, Sverige ), officially the Kingdom of Sweden ( sv, links=no, Konungariket Sverige ), is a Nordic countries, Nordic country in Northern Europe.The United Nations Group of Experts on Geographical Names states that the country's for ...

,
Denmark Denmark ( da, Danmark, ) is a Nordic countries, Nordic country in Northern Europe. It is the most populous and politically central Constituent state, constituent of the Danish Realm, Kingdom of Denmark, da, Kongeriget Danmark, a constitution ...

, the
Netherlands The Netherlands ( nl, Nederland ), informally referred to as Holland, is a country primarily located in Western Europe and partly in the Dutch Caribbean, Caribbean. It is the largest of four Kingdom of the Netherlands#Constituent countries, cons ...

and possibly
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin , coordinates = , largest_city = capital , languages_type = Official language , languages = German language, German , demonym = Germans, German , government_ ...

or the 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 South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, ...
,
Canada Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean, Atlantic to the Pacific Ocean, Pacific and northward into the Arctic Ocea ...

,
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and more than 700 List of islands of New Zealand, smaller islands, coveri ...

,
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, alongside Nynorsk. Bokmål is the preferred ...

,
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 continent entirely in the Western Hemisphere and mostly in ...

,
Austria Austria, officially the Republic of Austria, is a landlocked country in the southern part of Central Europe, located on the Eastern Alps. It is composed of nine States of Austria, federated states, one of which is Vienna, Austria's ca ...

,
Switzerland ,german: Schweizer(in),french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under a multi-party assembly-independent Directorial system, directorial republic , leader_t ...

,
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in the ...

, 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 continent entirely in the Western Hemisphere and mostly in ...

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, alongside Nynorsk. Bokmål is the preferred ...

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>

*
Hydraulic engineering Hydraulic engineering as a sub-discipline of civil engineering Civil engineering is a Regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and ...
*
International Rivers International Rivers is a non-profit A nonprofit organization (NPO), also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benef ...
*
List of energy storage projects This is a list of energy storage power plants worldwide, other than pumped hydro storage. Many individual energy storage plants augment electrical grids by capturing excess electrical energy during periods of low demand and storing it in other ...
*
List of hydroelectric power station failures This is a list of major hydroelectric power station failures due to damage to a hydroelectric power station Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "water"), als ...
*
List of largest power stations This article lists the largest 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 ...
*
List of renewable energy topics by country This is a list of renewable energy topics by country and territory. These links can be used to compare developments in renewable energy in different countries and territories and to help and encourage new writers to participate in writing about ...
* Lists of hydroelectric power stations * Marine current power - electricity from sea currents *
Renewable energy transition The renewable energy transition is the ongoing energy transition which is Fossil fuel phase-out, replacing fossil fuels with renewable energy. This transition can impact many aspects of life including the environment, society, the economy and gov ...