Hydroelectric Energy
Hydroelectricity is electricity generated by hydropower. The production of electrical power through the use of the gravitational force of falling or flowing water. Most hydroelectric power is generated using the potential energy of dammed water powering a turbine and a generator.
Renewable or Non-Renewable
Hydroelectricity is a renewable source of energy, as it made by harnessing the energy in moving water. The Niagara Falls hydroelectric power plants are good examples, existing as they are on both the American and Canadian sides of the border. The energy comes from using the great power of the falling water to turn giant turbines. These spinning turbines are connected to giant generators, and the spinning creates electricity that is put on the power grid system. As long as there is running water, there is power stored in it.
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Generating Methods
The 5 most common methods to generate hydroelectric are conventional (Dams), pumped storage, run-of-the-river, tide and underground.
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. The amount of potential energy in water is proportional to the head. A large pipe called the penstock delivers water to the turbine. See diagram above for further details.
This method 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 most commercially important means of large-scale grid energy storage 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.
Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that the water coming from upstream must be used for generation at
that moment, or must be allowed to bypass the dam. In the United States, run of the river hydropower could potentially provide 60,000 MW.
that moment, or must be allowed to bypass the dam. In the United States, run of the river hydropower could potentially provide 60,000 MW.
A tidal power plant makes use of the daily rise and fall of ocean water due to tides. S4uch sources are highly predictable, and if conditions permit
construction of reservoirs, can also be dipatchable 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. In Great Britain, there are eight sites that could be developed, but they only have the potential to generate 20% of the electricity used in 2012.
construction of reservoirs, can also be dipatchable 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. In Great Britain, there are eight sites that could be developed, but they only have the potential to generate 20% of the electricity used in 2012.
An underground power station makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake. An underground tunnel is constructed to take water from the high reservoir to the generating hall built in an underground cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway.
History
The flowing of water has been around for billions of years. Over 2000 years ago the greeks used water as an energy source. The greeks used water to power water wheels which powered their machinery. Using water for electricity has only recently been introduced.
Usage
Hydroelectricity is currently being used all over the world as source of energy. Hydroelectric energy is renewable and admits very little greenhouse gases, as a result it is being used more and more frequently.
Advantages
Flexibility
Hydro is a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demands.
Low power costs
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. The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour. Hydroelectric plants have long economic lives, with some plants still in service after 50–100 years. Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation. Where a dam serves multiple purposes, a hydroelectric 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.
Reduced CO2 emissions
Since hydroelectric dams do not burn fossil fuels, they are claimed to not directly produce carbon dioxide. 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. One measurement of greenhouse gas related and other externality comparison between energy sources can be found in the ExternE project by the Paul Scherrer Institut and the University of Stuttgart which was funded by the European Commission. According to that study, hydroelectricity produces the least amount of greenhouse gases and externality of any energy source. Coming in second place was wind, third was nuclear energy, and fourth was solar photovoltaic. The
extremely positive greenhouse gas impact of hydroelectricity is found especially in temperate climates. The above study was for local energy in
Europe; presumably similar conditions prevail in North America and Northern Asia, which all see a regular, natural freeze/thaw cycle (with associated seasonal plant decay and regrowth). Lower positive impacts are found in the tropical regions, as it has been noted that the reservoirs of power plants in tropical regions
produce extremely negative amounts of methane.
Hydro is a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demands.
Low power costs
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. The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour. Hydroelectric plants have long economic lives, with some plants still in service after 50–100 years. Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation. Where a dam serves multiple purposes, a hydroelectric 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.
Reduced CO2 emissions
Since hydroelectric dams do not burn fossil fuels, they are claimed to not directly produce carbon dioxide. 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. One measurement of greenhouse gas related and other externality comparison between energy sources can be found in the ExternE project by the Paul Scherrer Institut and the University of Stuttgart which was funded by the European Commission. According to that study, hydroelectricity produces the least amount of greenhouse gases and externality of any energy source. Coming in second place was wind, third was nuclear energy, and fourth was solar photovoltaic. The
extremely positive greenhouse gas impact of hydroelectricity is found especially in temperate climates. The above study was for local energy in
Europe; presumably similar conditions prevail in North America and Northern Asia, which all see a regular, natural freeze/thaw cycle (with associated seasonal plant decay and regrowth). Lower positive impacts are found in the tropical regions, as it has been noted that the reservoirs of power plants in tropical regions
produce extremely negative amounts of methane.
Disadvantages
Ecosystem damage and loss of land
Hydroelectric power stations that use dams would submerge large areas of land due to the requirement of a reservoir. Large reservoirs required for the operation of hydroelectric power stations result in submersion of extensive areas upstream of the dams, destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir.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. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.
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. 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. 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%. Brazil in particular is vulnerable due to its heaving 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.
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.
Hydroelectric power stations that use dams would submerge large areas of land due to the requirement of a reservoir. Large reservoirs required for the operation of hydroelectric power stations result in submersion of extensive areas upstream of the dams, destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. The loss of land is often exacerbated by habitat fragmentation of surrounding areas caused by the reservoir.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. Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.
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. 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. 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%. Brazil in particular is vulnerable due to its heaving 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.
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.
Resources
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Hydroelectricity | Clean Energy | US EPA. (n.d.). US Environmental Protection
Agency. Retrieved March 20, 2013, from
http://www.epa.gov/cleanenergy/energy-and-you/affect/hydro.html
Hydroelectricity - The Canadian Encyclopedia. (n.d.). The Canadian
Encyclopedia. Retrieved March 20, 2013, from
http://www.thecanadianencyclopedia.com
Hydroelectric Power: How it works, USGS Water-Science School. (n.d.). USGS
Georgia Water Science Center - Home page. Retrieved March 20, 2013, from
http://ga.water.usgs.gov/edu/hyhowworks.