Everything about Hydroelectric Power totally explained
Hydroelectricity is a form of
hydropower, and is the most widely used form of
renewable energy. It produces no waste, and doesn't produce
carbon dioxide (CO
2) which contributes to
greenhouse gases. 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.
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.
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's 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 isn't 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 watts,
is height in meters,
is flow rate in cubic meters per second, and
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/s
2, 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.
Small-scale hydro-electric plants
Small hydro plants are those producing up to 10 megawatts, although projects up to 30 megawatts in North America are considered small hydro and have the same regulations. 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 don't 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 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
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 isn't 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 8 years of full generation.
Greenhouse gas emissions
Since hydroelectric dams don't burn fossil fuels, they don't 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, 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
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 . ), 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. 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
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. These emissions represent carbon already in the biosphere, not fossil deposits that had been sequestered from the carbon cycle.
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.
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.
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
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 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
In 2005,
Venezuela's hydroelectric power plants produced nearly 74 TWh
Old hydro-electric power stations
Northern hemisphere
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.
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 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.
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
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.
Major schemes under construction
| Name |
Maximum Capacity |
Country |
Construction started |
Scheduled completion |
Comments |
| Three Gorges Dam |
22,500 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 |
Construction once stopped due to lack of environmental impact study. |
| Longtan Dam |
6,300 MW |
China |
July 1 2001 |
December 2009 |
|
| Xiangjiaba Dam |
6,000 MW |
China |
November 26 2006 |
2015 |
|
| Nuozhadu Dam |
5,850 MW |
China |
2006 |
2017 |
|
| Jinping 2 Hydropower Station |
4,800 MW |
China |
January 30 2007 |
2014 |
To build this dam, 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 |
|
| Pubugou Dam |
3,300 MW |
China |
March 30 2004 |
2010 |
|
| Goupitan Dam |
3,000 MW |
China |
November 8 2003 |
2011 |
|
| Boguchan Dam |
3,000 MW |
Russia |
1980 |
2012 |
|
| Chapetón |
3,000 MW |
Argentina |
|
|
|
| Jinanqiao Dam |
2,400 MW |
China |
December 2006 |
2010 |
|
| Guandi Dam |
2,400 MW |
China |
Novermber 11 2007 |
2012 |
| Tocoma (Manuel Piar) |
2,160 MW |
Venezuela |
2004 |
2014 |
This new power plant would be the last development in the Low Caroni Basin totalizing six power plant in the same river, including the 10,000MW Guri Dam. |
| Bureya Dam |
2,010 MW |
Russia |
1978 |
2009 |
|
| Ahai Dam |
2,000 MW |
China |
July 27 2006 |
|
|
| Lower Subansiri Dam |
2,000 MW |
India |
2005 |
2009 |
|
Proposed Major Hydro-electric Project
| Name |
Maximum Capacity |
Country |
Construction starts |
Scheduled completion |
Comments |
| Red Sea dam |
50,000 MW |
Middle East |
Unknown |
Unknown |
Still in planning, would be largest dam in the world |
| Grand Inga |
40,000 MW |
Democratic Republic of the Congo |
2010 |
Unknown |
|
| Baihetan Dam |
12,000 MW |
China |
2009 |
2015 |
Still in planning |
| Wudongde Dam |
7,000 MW |
China |
2009 |
2015 |
Still in planning |
| Maji Dam |
4,200 MW |
China |
2008 |
2013 |
|
| Songta Dam |
4,200 MW |
China |
2008 |
2013 |
|
| Liangjiaren Dam |
4,000 MW |
China |
2009 |
2015 |
Still in planning |
| Jirau Dam |
3,300 MW |
Brazil |
2007 |
2012 |
|
| Pati Dam |
3,300 MW |
Argentina |
|
|
|
| Santo Antônio Dam |
3,150 MW |
Brazil |
2007 |
2012 |
|
| Guanyinyan Dam |
3,000 MW |
China |
2009 |
2015 |
Still in planning |
| Lianghekou Dam |
3,000 MW |
China |
2009 |
2015 |
|
| Lower Churchill |
2,800 MW |
Canada |
2009 |
2014 |
|
| Liyuan Dam |
2,400 MW |
China |
2008 |
|
|
| Dagangshan Dam |
2,300 MW |
China |
2009 |
2015 |
|
| Changheba Dam |
2,200 MW |
China |
2009 |
2015 |
|
| Ludila Dam |
2,100 MW |
China |
2009 |
2015 |
|
Further Information
Get more info on 'Hydroelectric Power'.
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