Hydroelectricity

Renewable energy
Biofuels Biomass Geothermal Hydro power Solar power Tidal power Wave power Wind power

Hydroelectricity is electricity generated by hydropower, i.e., the production of power through use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy. Once a hydroelectric complex is constructed, the project produces no direct waste, and has a considerably different output level of the greenhouse gas carbon dioxide (CO₂) than fossil fuel powered energy plants. Worldwide, hydroelectricity supplied an estimated 715,000 MWe in 2005. This was approximately 19% of the world's electricity (up from 16% in 2003), and accounted for over 63% of electricity from renewable sources.^[1]

Some jurisdictions do not consider large hydro projects to be a sustainable energy source, due to the human, economic and environmental impacts of dam construction and maintenance.

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 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.

A simple formula for approximating electric power production at a hydroelectric plant is: , where is Power in kilowatts, is height in meters, is flow rate in cubic meters per second, is acceleration due to gravity of 9.8 m/s², and is a coefficient of efficiency ranging from 0 to 1. Efficiency is often higher 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.

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. The Grand Coulee Dam, long the worlds largest, switched to support Alcoa aluminum in Bellingham, Washington for America's World War II airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminum 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. As of 2007 the Kárahnjúkar Hydropower Project in Iceland remains controversial.^[2]

Small-scale hydro-electric plants

Main article: Small hydro

Although large hydroelectric installations generate most of the world's hydroelectricity, some situations require small hydro plants. These are defined as plants producing up to 10 megawatts, or projects up to 30 megawatts in North America. A small hydro plant may be connected to a distribution grid or may provide power only to an isolated community or a single home. Small hydro projects generally do not require the protracted economic, engineering and environmental studies associated with large projects, and often can be completed much more quickly. A small hydro development may be installed along with a project for flood control, irrigation or other purposes, providing extra revenue for project costs. In areas that formerly used waterwheels for milling and other purposes, often the site can be redeveloped for electric power production, possibly eliminating the new environmental impact of any demolition operation. Small hydro can be further divided into mini-hydro, units around 1 MW in size, and micro hydro with units as large as 100 kW down to a couple of kW rating.

Small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity.^[1]

Small hydro units in the range 1 MW to about 30 MW are often available from multiple manufacturers using standardized "water to wire" packages; a single contractor can provide all the major mechanical and electrical equipment (turbine, generator, controls, switchgear), selecting from several standard designs to fit the site conditions. Micro hydro projects use a diverse range of equipment; in the smaller sizes industrial centrifugal pumps can be used as turbines, with comparatively low purchase cost compared to purpose-built turbines.

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, and no imports are needed.

Hydroelectric plants also tend to have longer economic lives than fuel-fired generation, with some plants now in service which were built 50 to 100 years ago.^[3] 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 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 8 years of full generation.^[4]

Greenhouse gas emissions

Since hydroelectric dams do not burn fossil fuels, they do not directly produce carbon dioxide (a greenhouse gas). 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.

Related activities

Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in 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.

Disadvantages

Recreational users must exercise extreme care when near hydroelectric dams, power plant intakes and spillways.^[5]

Environmental damage

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of the plant site. 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 been demolished (for example the Marmot Dam demolished in 2007)^[6] because of impact on fish. Turbine and power-plant designs that are easier on aquatic life are an active area of research. Mitigation measures such as fish ladders may be required at new projects or as a condition of re-licensing of existing projects.

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.^[7] Since turbine gates 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 use canals 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.

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 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.^[8] Although these emissions represent carbon already in the biosphere, not fossil deposits that had been sequestered from the carbon cycle, there is a greater amount of methane due to anaerobic decay, causing greater damage than would otherwise have occurred had the forest decayed naturally.

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.^[9]

Discussions to exclude hydropower facilities from obtaining carbon credits under the Clean Development Mechanism are starting to take place, most recently at the UN Climate Change Conference 2007 in Bali, Indonesia.^[10]

Population relocation

Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In February 2008, it was estimated that 40-80 million people worldwide had been physically displaced as a direct result of dam construction.^[11] 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.

Affected by flow shortage

Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Because of global warming, the volume of glaciers has decreased, such as the North Cascades glaciers, which have lost a third of their volume since 1950, resulting in stream flows that have decreased by as much as 34%.^[12] The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power.

Comparison with other methods of power generation

The hydroelectric power station of Aswan Dam, Egypt

Hydroelectric Reservoir Vianden, Luxembourg

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. 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.

In parts of Canada (the provinces of British Columbia, Manitoba, Ontario, Quebec, Newfoundland and Labrador) hydroelectricity is used so extensively that the word "hydro" is often 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.

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 capacity factor. The installed capacity is the sum of all generator nameplate power ratings. Sources came from BP Annual Report 2006^[13] List of the largest hydoelectric power stations

Country	Annual Hydroelectric Energy Production(TWh)	Installed Capacity (GW)	Capacity Factor
People's Republic of China(2007)[14]	486.7	145.26	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
Venezuela	74[15]	-	-
Paraguay	64.0	-	-
Sweden	61.8	-	-
France	61.5	25.335	0.25

Old hydro-electric power stations

Northern hemisphere

• Appleton, Wisconsin, USA completed 1882, A waterwheel on the Fox river supplied the first commercial hydroelectric power for lighting to two paper mills and a house, two years after Thomas Edison demonstrated incandescent lighting to the public. Within a matter of weeks of this installation, a power plant was also put into commercial service at Minneapolis.

• 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.

• Decew Falls 1, St. Catharines, Ontario, Canada completed 25 August 1898. Owned by Ontario Power Generation. Four units are still operational. Recognized as an IEEE Milestone in Electrical Engineering & Computing by the IEEE Executive Committee in 2002.

• Claverack Creek, in Stottville, New York, believed to be the oldest hydro power site in the United States. 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 to generate electricity. It is owned today by Edison Hydro.

• 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.^[16]

• 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. NB Power now owns and operates this as part of the Milltown Dam hydroelectric station.

Southern hemisphere

• A small hydroelectric station, generating 650 kW, opened at Waratah, Tasmania, in 1885
• 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.
• Chivilingo was the first hydroelectric plant in Chile and the second in South America. With first power produced in 1897, it has two Pelton wheel turbines each turning a 215 kW generator. It was installed to provide power to mines and the city of Lota, Chile.^[17]
• The Snowy Mountains Scheme has turbines all along the tunnel so it, in some perspectives it is also another hydroelectric station. However it only operates during peak hours of the day and mostly during the evening and early night. It supplies electricity to all over the state of NSW.

Major schemes under construction

Proposed major hydroelectric projects

Cost

United States

In the United States, a study is required before constructing a hydroelectric project. In 2008, a study could cost up to $50,000 for a 100 feet (30 m) run of a stream. Both federal and state licenses were required. A license typically cost between $150,000 and $1 million. A project earns money from the sale of energy, the sale of capacity, and the sale of renewable energy credits.^[19]

See also

Renewable energy
Biofuels Biomass Geothermal Hydro power Solar power Tidal power Wave power Wind power

• Hydropower
• Run-of-the-river hydroelectricity
• List of countries by renewable electricity production
• List of reservoirs and dams
• Environmental impacts of dams
• List of the largest hydroelectric power stations
• Small hydro
• Pumped-storage hydroelectricity
• Environmental concerns with electricity generation
• Water power engine
• Category:Hydroelectric power plants by country

Notes

References

• New Scientist report on greenhouse gas production by hydroelectric dams.
• International Water Power and Dam Construction Venezuela country profile
• International Water Power and Dam Construction Canada country profile
• Tremblay, Varfalvy, Roehm and Garneau. 2005. Greenhouse Gas Emissions - Fluxes and Processes, Springer, 732 p.

External links

• Hydroelectricity at the Open Directory Project
• World Commission on Dams Report
• Mechanicville Hydroelectric Station Tour Video
• National Hydropower Association, USA
• Hydropower Reform Coalition, USA
• Interactive site that demonstrates dams' effects on rivers
• Center of expertise on hydropower impacts on fish and fish habitat, Canada
• Hydro-Québec
• CBC Digital Archives – Hydroelectricity: The Power of Water
• University of Washington Libraries – Seattle Power and Water Supply Collection
• International Rivers
• United States Federal Energy Regulatory Commission (FERC)
• European Small Hydropower Association
• Power at Niagara Falls Niagara Falls Public Library (Ont.)
• Milford Hydroelectric Station Restoration Tour Built by Henry Ford in 1939