# Hydroelectricity

Last updated

2019 world electricity generation by source (total generation was 27 petawatt-hours) [1] [2]

## Contents

Coal (37%)
Natural gas (24%)
Hydro (16%)
Nuclear (10%)
Wind (5%)
Solar (3%)
Other (5%)

Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and also more than nuclear power. [3]

Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. [3] A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel powered energy plants. [4] However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.

Construction of a hydroelectric complex can have significant environmental impact, principally in loss of arable land and population displacement. They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding, dam failure 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. In the mid-1770s, French engineer Bernard Forest de Bélidor published Architecture Hydraulique, which described vertical- and horizontal-axis hydraulic machines, and in 1771 Richard Arkwright’s combination of water power, the water frame, and continuous production played a significant part in the development of the factory system, with modern employment practices. [6] In the 1840s the hydraulic power network was developed to generate and transmit hydro power to end users.

By the late 19th century, the electrical generator was developed and could now be coupled with hydraulics. [7] The growing demand arising from the Industrial Revolution would drive development as well. [8] In 1878, the world's first hydroelectric power scheme was developed at Cragside in Northumberland, England, by William Armstrong. It was used to power a single arc lamp in his art gallery. [9] The old Schoelkopf Power Station No. 1, US, near Niagara Falls, began to produce electricity in 1881. The first Edison hydroelectric power station, the Vulcan Street Plant, began operating September 30, 1882, in Appleton, Wisconsin, with an output of about 12.5 kilowatts. [10] 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. [7]

At the beginning of the 20th century, many small hydroelectric power stations were being constructed by commercial companies in mountains near metropolitan areas. Grenoble, France held the International Exhibition of Hydropower and Tourism, with over one million visitors. By 1920, when 40% of the power produced in the United States was hydroelectric, the Federal Power Act was enacted into law. The Act created the Federal Power Commission 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, irrigation and navigation. Federal funding became necessary for large-scale development, and federally owned corporations, such as the Tennessee Valley Authority (1933) and the Bonneville Power Administration (1937) were created. [8] Additionally, the Bureau of Reclamation 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. [11] The United States Army Corps of Engineers was also involved in hydroelectric development, completing the Bonneville Dam in 1937 and being recognized by the Flood Control Act of 1936 as the premier federal flood control agency. [12]

Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as "white coal". [13] Hoover Dam's initial 1,345 MW power station was the world's largest hydroelectric power station in 1936; it was eclipsed by the 6,809 MW Grand Coulee Dam in 1942. [14] The Itaipu Dam opened in 1984 in South America as the largest, producing 14 GW, but was surpassed in 2008 by the Three Gorges Dam in China at 22.5 GW. Hydroelectricity would eventually supply some countries, including Norway, Democratic Republic of the Congo, Paraguay and Brazil, with over 85% of their electricity.

## Future potential

In 2021 the IEA said that more efforts are needed to help limit climate change. [15] Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%. [16]

### Modernization of existing infrastructure

In 2021 the IEA said that major modernisation refurbishments are required. [3] :67

## Generating methods

Cross-section of a conventional hydroelectric dam
Pumped-storage
Run-of-the-river
Tidal

### Conventional (dams)

Most hydroelectric power comes from the potential energy of dammed water driving a 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. A large pipe (the "penstock") delivers water from the reservoir to the turbine. [17]

### Pumped-storage

This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir, thus providing demand side response. [3] When the demand becomes greater, water is released back into the lower reservoir through a turbine. In 2021 pumped-storage schemes provided almost 85% of the world's 190 GW of grid energy storage [3] and improve the daily capacity factor of the generation system. Pumped storage is not an energy source, and appears as a negative number in listings. [18]

### 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. [19]

### Tide

A tidal power 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 or undammed sources such as undershot water wheels. Tidal power is viable in a relatively small number of locations around the world. [20]

## Sizes, types and capacities of hydroelectric facilities

### Large facilities

The largest power producers in the world are hydroelectric power stations, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations.

Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundred megawatts are generally considered large hydroelectric facilities.

Currently, only five facilities over 10 GW (10,000 MW ) are in operation worldwide, see table below. [21]

RankStationCountry Location Capacity (MW)
1. Three Gorges Dam   China 22,500
2. Itaipu Dam   Brazil
Paraguay
14,000
3. Xiluodu Dam   China 13,860
4. Belo Monte Dam   Brazil 11,233
5. Guri Dam   Venezuela 10,200

Panoramic view of the Itaipu Dam, with the spillways (closed at the time of the photo) on the left. In 1994, the American Society of Civil Engineers elected the Itaipu Dam as one of the Seven Wonders of the Modern World. [22]

### Small

Small hydro is hydroelectric power 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 megawatts (MW) is generally accepted as the upper limit. This may be stretched to 25 MW and 30 MW in Canada and the United States. [23] [24]

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

### Micro

Micro hydro means hydroelectric power installations that typically produce up to 100 kW 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. [25] Micro hydro systems complement photovoltaic 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 hydroelectric power generation of under 5 kW . 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 charger, or a small TV/radio). [26] Even smaller turbines of 200-300 W may power a few homes in a developing country with a drop of only 1 m (3 ft). 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 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:

${\displaystyle P=-\eta \ ({\dot {m}}g\ \Delta h)=-\eta \ ((\rho {\dot {V}})\ g\ \Delta h)}$

where

• ${\displaystyle P}$ is power (in watts)
• ${\displaystyle \eta }$ (eta) is the coefficient of efficiency (a unitless, scalar coefficient, ranging from 0 for completely inefficient to 1 for completely efficient).
• ${\displaystyle \rho }$ (rho) is the density of water (~1000  kg/m3)
• ${\displaystyle {\dot {V}}}$ is the volumetric flow rate (in m3/s)
• ${\displaystyle {\dot {m}}}$ is the mass flow rate (in kg/s)
• ${\displaystyle \Delta h}$ (Delta h) is the change in height (in meters)
• ${\displaystyle g}$ 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.[ citation needed ]

## 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. [21] Hydro turbines have a start-up time of the order of a few minutes. [27] Although battery power is quicker its capacity is tiny compared to hydro. [3] It takes less than 10 minutes to bring most hydro units from cold start-up to full load; this is quicker than nuclear and almost all fossil fuel power. [28] Power generation can also be decreased quickly when there is a surplus power generation. [29] 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. [30] Instead, it can serve as backup for non-hydro generators. [29]

#### High value power

The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost for dispatch later as high value clean electricity. In 2021 the IEA estimated that the "reservoirs of all existing conventional hydropower plants combined can store a total of 1 500 terawatt-hours (TWh) of electrical energy in one full cycle" which was "about 170 times more energy than the global fleet of pumped storage hydropower plants". [3] Battery storage capacity is not expected to overtake pumped storage during the 2020s. [3] When used as peak power to meet demand, hydroelectricity has a higher value than baseload power and a much higher value compared to intermittent energy sources such as wind and solar.

Hydroelectric stations have long economic lives, with some plants still in service after 50–100 years. [31] 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 will cover the construction costs after 5 to 8 years of full generation. [32] 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. [33]

#### 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 electrolytic plants, for example. The Grand Coulee Dam switched to support Alcoa aluminium in Bellingham, Washington, United States for American World War II airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. In Suriname, the Brokopondo Reservoir was constructed to provide electricity for the Alcoa aluminium industry. New Zealand's Manapouri Power Station was constructed to supply electricity to the aluminium smelter at Tiwai Point.

#### Reduced CO2 emissions

Since hydroelectric dams do not use fuel, power generation does not produce 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. [34] The low greenhouse gas impact of hydroelectricity is found especially in temperate climates. 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 than those in temperate areas. [35]

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, and become tourist attractions themselves. In some countries, aquaculture in reservoirs is common. Multi-use dams installed for irrigation support agriculture with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. [36] Managing dams which are also used for other purposes, such as irrigation, is complicated. [3]

In 2021 the IEA called for "robust sustainability standards for all hydropower development with streamlined rules and regulations". [3]

#### 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. [21] The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir. [37]

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems 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. [38] Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.

#### Drought and water loss by evaporation

Drought and seasonal changes in rainfall can severely limit hydropower. [3] Water may also be lost by evaporation. [39]

#### 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 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. [40] [41]

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. [42] One study from the 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%. [42] 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. [42]

#### Methane emissions (from reservoirs)

Lower positive impacts are found in the tropical regions. In lowland 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. [43] This is due to plant material in flooded areas decaying in an anaerobic environment and forming methane, a greenhouse gas. According to the World Commission on Dams report, [44] 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. [45]

In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions 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. [46]

#### 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. [47]

#### 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 in Southern China failed when more than a year's worth of rain fell within 24 hours (see 1975 Banqiao Dam failure). 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 in Italy, where almost 2,000 people died. [48]

The Malpasset Dam failure in Fréjus on the French Riviera (Côte d'Azur), southern France, collapsed on December 2, 1959, killing 423 people in the resulting flood. [49]

Smaller dams and micro hydro 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. [50]

### 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 in the coal. Hydroelectricity also avoids the hazards of coal mining and the indirect health effects of coal emissions. In 2021 the IEA said that government energy policy should "price in the value of the multiple public benefits provided by hydropower plants". [3]

#### Nuclear power

Nuclear power is relatively inflexible; although it can reduce its output reasonably quickly. Since the cost of nuclear power is dominated by its high infrastructure costs, the cost per unit energy goes up significantly with low production. Because of this, nuclear power is mostly used for baseload. By way of contrast, hydroelectricity can supply peak power at much lower cost. Hydroelectricity is thus often used to complement nuclear or other sources for load following. Country examples where they are paired in a close to 50/50 share include the electric grid in Switzerland, the Electricity sector in Sweden and to a lesser extent, Ukraine and the Electricity sector in Finland.

#### Wind power

Wind power goes through predictable variation by season, but is intermittent on a daily basis. Maximum wind generation has little relationship to peak daily electricity consumption, the wind may peak at night when power 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.

An example of this is Norway's trading with Sweden, Denmark, the Netherlands, Germany and the UK. [51] [52] Norway is 98% hydropower, while its flatland neighbors have wind power. In areas that do not have hydropower, pumped storage serves a similar role, but at a much higher cost and 20% lower efficiency.[ citation needed ]

## 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. [53] Hydropower is produced in 150 countries,[ citation needed ] 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, Canada, New Zealand, Norway, Paraguay, Austria, Switzerland, Venezuela, and several other countries have a majority of the internal electric energy production from hydroelectric power. Paraguay produces 100% of its electricity from hydroelectric dams and exports 90% of its production to Brazil and to Argentina. Norway produces 96% of its electricity from hydroelectric sources. [54] Large plants tend to be built by governments, so although in 2021 nearly 70% of plants were owned and operated by the private sector but 70% of capacity was publicly owned. [3]

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 installed capacity is the sum of all generator nameplate power ratings. [55]

Ten of the largest hydroelectric producers as at 2020. [56]
CountryAnnual hydroelectric
production (TWh)
Installed
capacity (GW)
Capacity
factor
% of world's
production
% in domestic
electricity
generation
China 12323520.3728.5%17.2%
Brazil 3891050.569.0%64.7%
United States 3171030.427.3%7.1%
Russia 193510.424.5%17.3%
India 151490.433.5%9.6%
Norway 140330.493.2%95.0%
Japan 88500.372.0%8.4%
Vietnam 84180.671.9%34.9%
France 71260.461.6%12.1%
Installed hydroelectricity power capacity (MW) [57]
#Country or territory2020
1 China370 160
2 Brazil109 318
3 United States103 058
5 Russia51 811
6 India50 680
7 Japan50 016
8 Norway33 003
9 Turkey30 984
10 France25 897
11 Italy22 448
12 Spain20 114
13 Vietnam18 165
14 Venezuela16 521
15 Sweden16 479
16 Switzerland15 571
17 Austria15 147
18 Iran13 233
19 Mexico12 671
20 Colombia12 611
21 Argentina11 348
22 Germany10 720
23 Pakistan10 002
24 Paraguay8 810
25 Australia8 528
26 Laos7 376
27 Portugal7 262
28 Chile6 934
29 Romania6 684
30 South Korea6 506
31 Ukraine6 329
32 Malaysia6 275
33 Indonesia6 210
34 Peru5 735
35 New Zealand5 389
36 Tajikistan5 273

## Economics

The weighted average cost of capital is a major factor. [3]

## Related Research Articles

Hydropower, 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 gravitational potential or kinetic energy of a water source to produce power. Hydropower is a method of sustainable energy production.

A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid.

Small hydro is the development of hydroelectric power on a scale suitable for local community and industry, or to contribute to distributed generation in a regional electricity grid. Exact definitions vary, but a "small hydro" project is less than 50 megawatts (MW), and can be further subdivide by scale into "mini" (<1MW), "micro" (<100 kW), "pico" (<10 kW). In contrast many hydroelectric projects are of enormous size, such as the generating plant at the Three Gorges Dam at 22,500 megawatts or the vast multiple projects of the Tennessee Valley Authority.

Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power. Although the losses of the pumping process make the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. If the upper lake collects significant rainfall or is fed by a river then the plant may be a net energy producer in the manner of a traditional hydroelectric plant.

Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amount of storage, in which case the storage reservoir is referred to as pondage. A plant without pondage is subject to seasonal river flows, thus the plant will operate as an intermittent energy source. Conventional hydro uses reservoirs, which regulate water for flood control, dispatchable electrical power, and the provision of fresh water for agriculture.

According to the International Hydropower Association, Canada is the fourth largest producer of hydroelectricity in the world in 2021 after the United States, Brazil, and China. In 2014, Canada consumed the equivalent of 85.7 megatonnes worth of oil of hydroelectricity, 9.8% of worldwide hydroelectric consumption. Furthermore, hydroelectricity accounted for 25.7% of Canada's total energy consumption. It is the third-most consumed energy in Canada behind oil and natural gas.

Hydroelectric power in New Zealand has been a part of the country's energy system for over 100 years and continues to provide more than half of the country's electricity needs. Hydroelectricity is the primary source of renewable energy in New Zealand. Power is generated the most in the South Island and is used most in the North Island.

Low-head hydropower refers to the development of hydroelectric power where the head is typically less than 20 metres, although precise definitions vary. Head is the vertical height measured between the hydro intake water level and the water level at the point of discharge. Using only a low head drop in a river or tidal flows to create electricity may provide a renewable energy source that will have a minimal impact on the environment. Since the generated power is a function of the head these systems are typically classed as small-scale hydropower, which have an installed capacity of less than 5MW.

Hydroelectricity is, as of 2019, the second-largest renewable source of energy in both generation and nominal capacity in the United States. In 2021, hydroelectric power produced 31.5% of the total renewable electricity, and 6.3% of the total U.S. electricity.

Richard B. Russell Dam is a concrete-gravity and embankment dam located on the Savannah River at the border of South Carolina and Georgia, creating Richard B. Russell Lake. The dam was built by the U.S. Army Corps of Engineers between 1974 and 1985 for the purposes of flood control, hydroelectricity, recreation, additional stream flow regulation, water supply, and fish and wildlife management. The concrete structure of the dam spans 1,904 feet (580 m) and rises 210 feet (64 m) above the riverbed, housing a hydro-power plant with an installed 600 megawatts (800,000 hp) capacity. The Richard B. Russell Dam is the final large dam completed by the U.S. Army Corps in the Savannah River Basin and lies 30 miles downstream from the Hartwell Dam (1962) and 37 miles (60 km) upstream from the J. Strom Thurmond Dam (1954).

Policy makers often debate the constraints and opportunities of renewable energy.

India is 5th globally for installed hydroelectric power capacity. As of 31 March 2020, India's installed utility-scale hydroelectric capacity was 46,000 MW, or 12.3% of its total utility power generation capacity. Additional smaller hydroelectric power units with a total capacity of 4,683 MW have been installed. India's hydroelectric power potential is estimated at 148,700 MW at 60% load factor. In the fiscal year 2019–20, the total hydroelectric power generated in India was 156 TWh with an average capacity factor of 38.71%.

The Ubol Ratana Dam, formerly known as the "Phong Neeb Dam", is a multi-purpose dam in tambon Khok Sung, Ubolratana district, approximately 50 km (31 mi) north of Khon Kaen, Khon Kaen province, Thailand. It was the first hydroelectric power project developed in Thailand's northeastern area of Isan. The dam impounds the Nam Phong, which flows into the Chi River and thence to the Mun River, a tributary of the Mekong River. The dam was given its current name by royal permission in 1966, in honour of princess Ubol Ratana, the eldest child of King Bhumibol Adulyadej.

The Cirata Dam is an embankment dam on the Citarum River in West Java, Indonesia. It is located 100 km (62 mi) southeast of Jakarta. It was constructed between 1984 and 1988 for the primary purpose of hydroelectric power generation. Other purposes include flood control, aquaculture, water supply and irrigation. The 125 m (410 ft) tall concrete-face rock-fill dam is situated just before a sharp bend in the river and withholds a reservoir with a gross storage capacity of 2,165,000,000 m3 (1,755,194 acre⋅ft). The reservoir has a surface area of 62 km2 (24 sq mi) which caused the relocation of 6,335 families. The dam's power station is located on the north side of the river bend and contains eight 126 MW Francis turbine-generators. It has a total installed capacity of 1,008 MW and an annual generation of 1,426 GWh. The power station was completed in two phases, the second was completed in 1998. It serves mostly as a peaking power plant and is the largest hydroelectric power station in Indonesia. The construction of the dam resulted in involuntary resettlement of 56,000 people.

The Minghu Dam (Chinese: 明湖水壩; pinyin: Mínghú Shuǐbà, renamed the Takuan Dam, is a concrete gravity dam on the Shuili River located 7 km north of Shuili Township in Nantou County, Taiwan. The reservoir formed by the dam serves as the lower reservoir for the Minhu Pumped Storage Hydro Power Station. Sun Moon Lake serves as the upper reservoir.

The Okuyoshino Pumped Storage Power Station (奥吉野発電所) is located 15 kilometres (9.3 mi) north of Totsukawa in Nara Prefecture, Japan. Using the pumped-storage hydroelectric method, the power plant has an installed capacity of 1,206 megawatts (1,617,000 hp). To accomplish power generation, the power station shifts water between two reservoirs, the lower Asahi Reservoir and the upper Seto Reservoir. Construction on both the Asahi and Seto Dams began in 1971 and was complete in 1978. The power station was commissioned in 1980. Due to heavy sediment and turbidity in the Seto Reservoir, caused by logging and landslides upstream, a sediment bypass tunnel was constructed between 1992 and 1998.

Hydroelectricity is a major source of electricity in Turkey, due to its mountainous landscape and many rivers. The country's main river basins are those of the Euphrates and the Tigris. Over 700 hydropower plants have been built, and hydroelectricity makes up about 30% of the country's electricity generating capacity. Generation can vary greatly from one year to the next, depending on rainfall. In good years, substantial amounts of hydroelectric power can be generated. Government policies have generally supported dam construction, but some dams are controversial in neighbouring countries, while others raise concerns about damage to the environment and wildlife of Turkey.

Thailand has set targets and policies for the development of its energy sector for 2035, with priority being given to indigenous renewable energy resources, including hydropower.

Hydroelectricity is currently China's largest renewable energy source and the second overall after coal. China's installed hydroelectric capacity in 2015 was 356 GW, up from 172 GW in 2009, including 23 GW of pumped storage hydroelectricity capacity. According to the International Hydropower Association China is the worlds largest producer of hydroelectricity in 2021. In 2018, hydropower generated 1,232 TWh of power, accounting for roughly 18% of China's total electricity generation.

The power generation potential of the rivers in Azerbaijan is estimated at 40 billion kilowatt per hour, and feasible potential is 16 billion kilowatt per hour. Small-scale hydro has significant developmental potential in Azerbaijan. In particular, the lower reaches of the Kura river, the Aras river and other rivers flowing into the Caspian Sea. Hydropower could conceivably provide up to 30% of Azerbaijan’s electricity requirements. Currently, hydropower, dominated by large-scale dams, provides 11.4% of Azerbaijan’s electricity.

## References

1. "Data & Statistics". International Energy Agency . Retrieved 2021-11-25.
2. "World gross electricity production by source, 2019 – Charts – Data & Statistics". International Energy Agency . Retrieved 2021-11-25.
3. "Hydropower Special Market Report – Analysis". IEA. Retrieved 2022-01-30.
4. Renewables 2011 Global Status Report, page 25, Hydropower, REN21 , published 2011, accessed 2016-02-19.
5. One of the Oldest Hydroelectric Power Plants in Europa Built on Tesla’s Principels, Explorations in the History of Machines and Mechanisms: Proceedings of HMM2012, Teun Koetsier and Marco Ceccarelli, 2012.
6. Maxine Berg, The age of manufactures, 1700-1820: Industry, innovation and work in Britain (Routledge, 2005).
7. "History of Hydropower". U.S. Department of Energy.
8. "Hydroelectric Power". Water Encyclopedia.
9. Association for Industrial Archaeology (1987). Industrial archaeology review, Volumes 10-11. Oxford University Press. p. 187.
10. "Boulder Canyon Project Act" (PDF). December 21, 1928. Archived from the original (PDF) on June 13, 2011.
11. "Hydropower". The Book of Knowledge. Vol. 9 (1945 ed.). p. 3220.
12. "Hoover Dam and Lake Mead". U.S. Bureau of Reclamation.
13. "Hydropower – Analysis". IEA. Retrieved 2022-01-30.
14. "Renewable Energy Essentials: Hydropower" (PDF). IEA.org. International Energy Agency. Archived from the original (PDF) on 2017-03-29. Retrieved 2017-01-16.
15. "Hydroelectricity - Renewable Energy Generation". www.electricityforum.com.
16. "Pumped Storage, Explained". Archived from the original on December 31, 2012.
17. "Run-of-the-River Hydropower Goes With the Flow". 31 January 2012.
18. "Energy Resources: Tidal power". www.darvill.clara.net.
19. Hemanth Kumar (March 2021). "World's biggest hydroelectric power plants" . Retrieved 2022-02-05.{{cite web}}: CS1 maint: url-status (link)
20. Pope, Gregory T. (December 1995), "The seven wonders of the modern world", Popular Mechanics, pp. 48–56
21. Renewables Global Status Report 2006 Update Archived July 18, 2011, at the Wayback Machine , REN21 , published 2006
22. Renewables Global Status Report 2009 Update Archived July 18, 2011, at the Wayback Machine , REN21 , published 2009
23. "Micro Hydro in the fight against poverty". Tve.org. Archived from the original on 2012-04-26. Retrieved 2012-07-22.
24. "Pico Hydro Power". T4cd.org. Archived from the original on 2009-07-31. Retrieved 2010-07-16.
25. Robert A. Huggins (1 September 2010). Energy Storage. Springer. p. 60. ISBN   978-1-4419-1023-3.
26. "About 25% of U.S. power plants can start up within an hour - Today in Energy - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2022-01-30.
27. Bent Sørensen (2004). Renewable Energy: Its Physics, Engineering, Use, Environmental Impacts, Economy, and Planning Aspects. Academic Press. pp. 556–. ISBN   978-0-12-656153-1.
28. Geological Survey (U.S.) (1980). Geological Survey Professional Paper. U.S. Government Printing Office. p. 10.
29. "Beyond Three Gorges in China". Waterpowermagazine.com. 2007-01-10. Archived from the original on 2011-06-14.
30. Ansar, Atif; Flyvbjerg, Bent; Budzier, Alexander; Lunn, Daniel (March 2014). "Should We Build More Large Dams? The Actual Costs of Hydropower Megaproject Development". Energy Policy. 69: 43–56. arXiv:. doi:10.1016/j.enpol.2013.10.069. S2CID   55722535. SSRN   2406852.
31. "2018 Hydropower Status Report: Sector Trends and Insights" (PDF). International Hydropower Association. 2018. p. 16. Retrieved 19 March 2022.
32. Wehrli, Bernhard (1 September 2011). "Climate science: Renewable but not carbon-free". Nature Geoscience. 4 (9): 585–586. Bibcode:2011NatGe...4..585W. doi:10.1038/ngeo1226.
33. Atkins, William (2003). "Hydroelectric Power". Water: Science and Issues. 2: 187–191.
34. Robbins, Paul (2007). "Hydropower". Encyclopedia of Environment and Society. 3.
35. "Sedimentation Problems with Dams". Internationalrivers.org. Archived from the original on 2010-10-01. Retrieved 2010-07-16.
36. John Macknick and others, A Review of Operational Water Consumption and Withdrawal Factors for Electricity Generating Technologies, National Renewable Energy Laboratory, Technical Report NREL/TP-6A20-50900.
37. Patrick James, H Chansen (1998). "Teaching Case Studies in Reservoir Siltation and Catchment Erosion" (PDF). Great Britain: TEMPUS Publications. pp. 265–275. Archived from the original (PDF) on 2009-09-02.
38. Șentürk, Fuat (1994). Hydraulics of dams and reservoirs (reference. ed.). Highlands Ranch, Colo.: Water Resources Publications. p. 375. ISBN   0-918334-80-2.
39. Frauke Urban and Tom Mitchell 2011. Climate change, disasters and electricity generation Archived September 20, 2012, at the Wayback Machine . London: Overseas Development Institute and Institute of Development Studies
40. "Deliberate drowning of Brazil's rainforest is worsening climate change", Daniel Grossman 18 September 2019, New Scientist ; retrieved 30 September 2020
41. "WCD Findal Report". Dams.org. 2000-11-16. Archived from the original on 2013-08-21.
42. Graham-Rowe, Duncan (24 February 2005). "Hydroelectric power's dirty secret revealed". NewScientist.com.
43. ""Rediscovered" Wood & The Triton Sawfish". Inhabitat. 2006-11-16.
44. "Briefing of World Commission on Dams". Internationalrivers.org. 2008-02-29. Archived from the original on 2008-09-13. Retrieved 2008-09-03.
45. References may be found in the list of Dam failures.
46. Bruel, Frank. "La catastrophe de Malpasset en 1959" . Retrieved 2 September 2015.
47. Toccoa Flood USGS Historical Site, retrieved 02sep2009
48. "Norway is Europe's cheapest "battery"". SINTEF.no. 18 December 2014.
49. "Germany and Norway commission NordLink power cable". Power Technology. 2021-05-28. Retrieved 2022-01-29.
50. Zervos, Arthouros (2016). Renewables 2016 Global Status Report (PDF). ISBN   978-3-9818107-0-7. Archived from the original (PDF) on 2019-01-24.
51. "Binge and purge". The Economist . 2009-01-22. Retrieved 2009-01-30. 98-99% of Norway’s electricity comes from hydroelectric plants.
52. "2020 Key World Energy Statistics". report. International Energy Agency (IEA). Retrieved 24 May 2021.
53. "Renewable Capacity Statistics 2021 page 17" (PDF). Retrieved 24 May 2021.