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Hydroelectricity

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Hydroelectricity is electricity produced by hydropower. Hydroelectricity now supplies about 715,000 MWe or 19% of world electricity (16% in 2003), accounting for over 63% of the total electricity from renewables in 2005.[1]

Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity.[1]

Renewable energy sources worldwide in 2005 (2004 for items marked * or **). Off-grid electric and ground source heat pumps not included. Source: REN21[1]

Electricity generation

Hydraulic turbine and electrical generator.
Hydroelectric dam in cross section
Main article: Electricity generation

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. In this case the energy 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. The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.

Pumped storage hydroelectricity produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped storage schemes currently provide the only commercially important means of large-scale grid energy storage and improve the daily load factor of the generation system. Hydroelectric plants with no reservoir capacity are called run-of-the-river plants, since it is not then possible to store water. A tidal power plant makes use of the daily rise and fall of water due to tides; such sources are highly predictable, and if conditions permit construction of barrages and 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 waterwheels, the relatively recent field of hydrokinetics.

Formula

A simple formula for approximating electric power production at a hydroelectric plant is:
P=hrk,
where P is Power in watts, h is height in meters, r is flow rate in cubic meters per second, and k is a conversion factor of 7500 watts (assuming an efficiency factor of about 76.5 percent and acceleration due to gravity of 9.81 m/s2, and fresh water with a density of 1000 kg per cubic metre. Efficiency is often higher with larger modern turbines and may be lower with very old or small installations due to proportionately higher friction losses).

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.

Industrial hydroelectric plants

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. In the Scottish Highlands there are examples at Kinlochleven and Lochaber, constructed during the early years of the 20th century. 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. As of 2007 the Kárahnjúkar Hydropower Project in Iceland remains controversial.[2]

Advantages

The upper reservoir and dam of the Ffestiniog pumped storage scheme. 360 megawatts of electricity can be generated within 60 seconds of the need arising.

Economics

The major advantage of hydroelectricity is elimination of the cost of fuel. The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil, natural gas or coal. Fuel is not required and so it need not be imported. Hydroelectric plants tend to have longer economic lives than fuel-fired generation, with some plants now in service having been built 50 to 100 years ago. Operating labor cost is usually low since plants are automated and have few personnel on site during normal operation.

Where a dam serves multiple purposes, a hydroelectric plant 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 7 years of full generation.[3]

Greenhouse gas emissions

Since no fossil fuel is consumed, emission of carbon dioxide (a greenhouse gas) from burning fuel is eliminated. While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation. However, there may be other sources of emissions as discussed below.

Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in themselves. In some countries, farming fish in the reservoirs is common. Multi-use dams installed for irrigation can support the fish farm with relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. When dams create large reservoirs and eliminate rapids, boats may be used to improve transportation.


Disadvantages

Recreational users must exercise extreme care when near hydroelectric dams, power plant intakes and spillways.[4]
Warning on embankment about sudden water release

Environmental damage

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems. For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed. Salmon spawn are also harmed on their migration to sea when they must pass through turbines. This has led to some areas transporting smolt downstream by barge during parts of the year. In some cases dams have actually been demolished, e.g. the Marmot Dam, because of impact on fish. The final phase of the Marmot Dam removal was completed on Saturday October 20th, 2007, when the temporary dam was demolished and the river started to flow freely for the first time in 100 years[5]. This was the largest dam removal project in the US. Turbine and power-plant designs that are easier on aquatic life are an active area of research.

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 turbines are often opened intermittently, rapid or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars. Dissolved oxygen content of the water may change from pre-construction conditions. Depending on the location, water exiting from turbines is typically much warmer than the pre-dam water, which can change aquatic faunal populations, including endangered species, and prevent natural freezing processes from occurring. Some hydroelectric projects also utilize canals, typically to divert a river at a shallower gradient to increase the head of the scheme. In some cases, the entire river may be diverted leaving a dry riverbed. Examples include the Tekapo and Pukaki Rivers.

Large-scale hydroelectric dams, such as the Aswan Dam and the Three Gorges Dam, have created environmental problems both upstream and downstream.

A further concern is the impact of major schemes on birds. Since damming and redirecting the waters of the Platte River in Nebraska for agricultural and energy use, many native and migratory birds such as the Piping Plover and Sandhill Crane have become increasingly endangered.

Greenhouse gas emissions

Bonnington hydroelectric power station, River Clyde, Scotland.
The pipes supplying water from the River Clyde to Bonnington hydroelectric power station, Scotland.

The reservoirs of smeg power plants in tropical regions may produce substantial amounts of methane and carbon dioxide. This is due to plant material in flooded areas decaying in an anaerobic environment, and forming methane, a very potent greenhouse gas. According to the World Commission on Dams 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.[6]

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.[7]

Population relocation

Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population. Additionally, historically and culturally important sites can be flooded and lost. Such problems have arisen at the Three Gorges Dam project in China, the Clyde Dam in New Zealand and the Ilısu Dam in Southeastern Turkey.

Dam failures

Failures of large dams, while rare, are potentially serious — the Banqiao Dam failure in Southern China resulted in the deaths of 171,000 people and left millions homeless. Dams may be subject to enemy bombardment during wartime, sabotage and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats.

The creation of a dam in a geologically inappropriate location may cause disasters like the one of the Vajont Dam in Italy, where almost 2000 people died, in 1963.

Comparison with other methods of power generation

Percentage of electricity coming from hydro by country. Some resource-rich low-population or low-GDP countries are able to supply all of their electricity needs from hydroelectricity, but in almost all cases, agressive electricity demand of a developed nation far exceeds what the rivers of the nation can provide.

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-burning [8].

Compared to nuclear power, hydroelectricity generates no nuclear waste, has none of the dangers associated with uranium mining, nor nuclear leaks. Unlike uranium, hydroelectricity is also a renewable energy source.

Compared to wind farms, hydroelectricity power plants have a more predictable load factor. If the project has a storage reservoir, it can be dispatched to generate power when needed. Hydroelectric plants can be easily regulated to follow variations in power demand.

Unlike fossil-fueled combustion turbines, construction of a hydroelectric plant requires a long lead-time for site studies, hydrological studies, and environmental impact assessment. Hydrological data up to 50 years or more is usually required to determine the best sites and operating regimes for a large hydroelectric plant. Unlike plants operated by fuel, such as fossil or nuclear energy, the number of sites that can be economically developed for hydroelectric production is limited; in many areas the most cost effective sites have already been exploited. New hydro sites tend to be far from population centers and require extensive transmission lines. Hydroelectric generation depends on rainfall in the watershed, and may be significantly reduced in years of low rainfall or snowmelt. Long-term energy yield may be affected by climate change. Utilities that primarily use hydroelectric power may spend additional capital to build extra capacity to ensure sufficient power is available in low water years.

File:Power plant Dnepr.jpg
The Dnieper Hydroelectric Station (1927-32) was the centerpiece of Lenin's GOELRO plan
File:Power Station of Aswan dam.jpg
The hydroelectric power station of Aswan Dam, Egypt
Hydroelectric Reservoir Vianden, Luxembourg

In parts of Canada (the provinces of British Columbia, Manitoba, Ontario, Quebec and Newfoundland and Labrador) hydroelectricity is used so extensively that the word "hydro" is used to refer to any electricity delivered by a power utility. The government-run power utilities in these provinces are called BC Hydro, Manitoba Hydro, Hydro One (formerly "Ontario Hydro"), Hydro-Québec and Newfoundland and Labrador Hydro respectively. Hydro-Québec is the world's largest hydroelectric generating company, with a total installed capacity (2005) of 31,512 MW.

Oldest hydro-electric power stations

  • Niagara Falls, New York. For many years the largest hydroelectric power station in the world. Operation began locally in 1895 and power was transmitted to Buffalo, New York, in 1896.
  • Duck Reach, Launceston, Tasmania. Completed 1895. The first publicly owned hydro-electric plant in the Southern Hemisphere. Supplied power to the city of Launceston for street lighting.
  • It is believed that the oldest Hydro Power site in the United States is located on Claverack Creek, in Stottville, New York. The turbine, a Morgan Smith, was constructed in 1869 and installed 2 years later. It is one of the earliest water wheel installations in the United States and also generated electricity. It is owned today by Edison Hydro. [citation needed]
  • The oldest continuously-operated commercial hydroelectric plant in the United States is built on the Hudson River at Mechanicville, New York. The seven 750 kW units at this station initially supplied power at a frequency of 38 Hz, but later were increased in speed to 40 Hz. It went into commercial service July 22,1898. It is now being restored to its original condition and remains in commercial operation. [9]
  • The oldest continuously-operated hydroelectric generator in Canada is located in St. Stephen, New Brunswick, Canada. Part of the construction of the Milltown Cotton Mill, this rope-driven generator originally powered the electric lights for the mill when it opened in 1882, and in 1888 started providing power to homes in the town. It is still turned by the original 1882 rope. NB Power now owns and operates this as part of the Milltown Dam hydroelectric station.

Countries with the most hydro-electric capacity

The ranking of hydro-electric capacity is either by actual annual energy production or by installed capacity power rating. A hydro-electric plant rarely operates at its full power rating over a full year; the ratio between annual average power and installed capacity rating is the load factor. The installed capacity is the sum of all generator nameplate power ratings. Sources came from BP Annual Report 2006
List of the largest hydoelectric power stations

Country Annual Hydroelectric Energy Production(TWh) Installed Capacity (GW) Load Factor
People's Republic of China [10] 416.7 128.57 0.37
Canada 350.3 88.974 0.59
Brazil 349.9 69.080 0.56
USA 291.2 79.511 0.42
Russia 157.1 45.000 0.42
Norway 119.8 27.528 0.49
India 112.4 33.600 0.43
Japan 95.0 27.229 0.37
Sweden 61.8 - -
France 61.5 25.335 0.25

Country, annual hydroelectricity production, installed capacity (2006 data including pumped storage schemes)[11]

Major schemes in progress

Name Maximum Capacity Country Construction started Scheduled completion Comments
Three Gorges Dam 22,400 MW China December 14 1994 2009 Largest power plant in the world. First power in July 2003, with 12,600 MW installed by October 2007.
Xiluodu Dam 12,600 MW China December 26 2005 2015
Baihetan Dam 12,000 MW China 2009 2015 Still in planning
Wudongde Dam 7,000 MW China 2009 2015 Still in planning
Longtan Dam 6,300 MW China July 1 2001 December 2009
Xiangjiaba Dam 6,000 MW China November 26 2006 2009
Jinping 2 Hydropower Station 4,800 MW China January 30 2007 2014 To build this dam, only 23 families and 129 local residents need to be moved. It works with Jinping 1 Hydropower Station as a group.
Laxiwa Dam 4,200 MW China April 18 2006 2010
Xiaowan Dam 4,200 MW China January 1 2002 December 2012
Jinping 1 Hydropower Station 3,600 MW China November 11 2005 2014
Jirau Dam 3,300 MW Brazil 2007 2012
Pubugou Dam 3,300 MW China March 30 2004 2010
Santo Antônio Dam 3,150 MW Brazil 2007 2012
Goupitan Dam 3,000 MW China November 8 2003 2011
Boguchan Dam 3,000 MW Russia 1980 2012
Guandi Dam 2,400 MW China 2007 2012
Son la Dam 2,400 MW Vietnam 2005
Bureya Dam 2,010 MW Russia 1978 2009
Lower Subansiri Dam 2000 MW India 2005 2009

Those 12 dams in China will have a total generating capacity of 89,400 MW (89.4 GW) when completed. For comparison purposes, in 2006 the total capacity of hydroelectric generators in Brazil, the third country by hydroelectric capacity, was 69,080 MW (69.08 GW).

See also

Part of a series on
Renewable energy
Wikimedia Commons has media related to Hydroelectric power.

References

  1. ^ a b c Renewables Global Status Report 2006 Update, REN21, published 2007, accessed 2007-05-16 Cite error: The named reference "REN21-2006" was defined multiple times with different content (see the help page).
  2. ^ Summer of International dissent against Heavy Industry, Saving Iceland, published 2007, accessed 2007-05-17
  3. ^ Beyond Three Gorges in China
  4. ^ Stay Clear, Stay Safe, Ontario Power Generation
  5. ^ "Rain helps Sandy River run wild, free". The Oregonian. October 20, 2007.
  6. ^ Hydroelectric power's dirty secret revealed
  7. ^ http://inhabitat.com/2006/12/01/rediscovered-wood-the-triton-sawfish/#more-1973
  8. ^ http://www.cleartheair.org/dirtypower/docs/abt_powerplant_whitepaper.pdf
  9. ^ The Historic Mechanicville Hydroelectric Station Part 1: The Early Days, IEEE Industry Applications Magazine, Jan/Feb. 2007
  10. ^ http://www.ctgpc.com.cn/sx/news.php?mNewsId=21623
  11. ^ Consumption TWh'!A1

Other references:

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