How can hydroelectric energy be used?
How can hydroelectric energy be used?
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Hydro means water which makes hydroelectricity a electricity generated using water.Usually huge dams are build near fast flowing rivers that can generate enough power through water waves.
What is water reservoir?
Yea, there is no such thing as a 1000m working head dam thatnk you very much...
How is hydroelectric energy used?
Hydroelectric energy is ultimately solar energy converted through evaporation of water, movement of air masses and precipitation to gravitational potential energy and then to the kinetic energy of water flowing down a slope.
This kinetic energy was harnessed for centuries through the use of water wheels to drive mills, forges and textile works, before being supplanted by coal-fired steam energy. Electricity generation using water turbines, although first centred on constricted streams, has increasingly focused on dams and reservoirs that store gravitational potential energy until it is needed.
World capacity of hydroelectric generation has increased every year for over a century and by 2002 had reached about 740 GigaWatts, by far the largest alternative contributor to global electricity supplies.
At the present time, large-scale hydroelectricity generation is increasing by about 50 TWh yr-1, although there are fluctuations related to the precipitation in any particular year. This illustrates an important point about hydroelectricity - despite its ultimate reliance on the combination of solar and gravitational energy, the immediate mediator of output is the water cycle.
The principle of hydroelectric power generation is simple - water flowing down steep gradients or from dams is channelled through pipes and transfers its kinetic energy to rotating turbines that drive electricity generators. Steep gradients ensure high flow speeds, and piping is necessary to maintain the pressure head.
Some energy is lost to friction and turbulent flow in the pipes, in turbine rotation, and in the conversion of mechanical energy to electricity in the generator. However, these losses are not great - indeed modern hydroelectric turbines have efficiencies exceeding 90%, so most of the potential energy of water stored in a reservoir can be converted into electricity.
The power developed depends on the product of the water discharge rate (Q , in m3 s-1 ) and the working head (the vertical fall of water flowing into the hydroelectric plant, H, in metres) as follows:
where N is the power output in W (= J s-1 ), g is the acceleration due to gravity (9.8 m s-2 ), ρ is the density of water (103 kg m-3 ) and K is the overall efficiency of the generating system.
Clearly, installations that have a large working head require smaller discharge rates for equivalent power output than do those with a small working head. Hence mountainous countries, such as Norway, Switzerland and New Zealand, can rely greatly on hydropower, often using small water flow rates, because working heads exceeding 1000 m are often available.
Today, almost all of Norway's electricity is produced by hydroelectric means (40% of its entire energy use). However, since most of the best sites for large working head installations have already been developed in industrialized nations, attention is turning to improving the economics of using working heads of only 20-30 m on more slowly flowing rivers. Even working heads less than 10 m can give useful yields.
The three main rivers that flow through the flat plains of India and Bangladesh (the Ganges, Brahmaputra and Meghna) discharge an average of 2.5 × 104 m3 s-1 to the Bay of Bengal. Their hydroelectric potential from single installations on each river is about 1 GW, using a 5 m head.
Similar capacities characterize the lower courses of most of the world's major rivers. But this is no more than the capacity of moderately sized fossil and nuclear fuel generating plants, so despite their potential to act as flood regulators as well as power generators, major rivers have proved unattractive for hydropower development low in their courses.
In the higher courses of major rivers they have lower discharges, but where they flow through narrow valleys and gorges it is possible to build higher dams (with higher working heads).
The Three Gorges Dam across the Yangtse River in China involves a dam 185 m high. With an average discharge of 1.3 × 104 m3 s-1 , it has a generating capacity of 18.2 GW, and will be the largest single hydropower project on the planet.