| Pumped Storage Hydroelectricity |
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Pumped storage hydroelectricity is a method of Storing and producing Electricity to supply high peak demands by moving water between Reservoirs at different elevations. OVERVIEW 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, generating electricity. Reversible turbine/generator assemblies act as pump and turbine (usually a Francis Turbine design). Some facilities use abandoned mines as the lower reservoir, but many use the height difference between two natural bodies of water or artificial reservoirs. Pure pumped-storage plants just shift the water between reservoirs, but combined pump-storage plants also generate their own electricity like conventional Hydroelectric Plants through natural stream-flow. Plants that do not use pumped-storage are referred to as conventional hydroelectric plants; conventional hydroelectric plants that have significant storage capacity may be able to play a similar role in the Electrical Grid as pumped storage, by deferring output until needed. Taking into account evaporation losses from the exposed water surface and conversion losses, approximately 70% to 85% of the electrical energy used to pump the water into the elevated reservoir can be regained. The technique is currently the most cost-effective means of storing large amounts of electrical energy on an operating basis, but capital costs and the presence of appropriate geography are critical decision factors. The relatively low energy density of pumped storage systems requires either a very large body of water or a large variation in height. For example, 1000 Kilogram s of water (1 Cubic Meter ) at the top of a 100 Meter tower has a potential energy of about 0.277 KW·h . The only way to store a significant amount of energy is by having a large body of water located on a hill relatively near, but as high as possible above, a second body of water. In some places this occurs naturally, in others one or both bodies of water have been man-made. This system may be economical because it flattens out load variations on the power grid, permitting thermal power stations such as Coal-fired Plants and Nuclear Power Plant s that provide base-load electricity to continue operating at peak efficiency ( Base Load Power Plant s), while reducing the need for "peaking" power plants that use costly fuels. Capital costs for purpose-built hydrostorage are high, however. Along with energy management, pumped storage systems help control electrical network Frequency and provide reserve generation. Thermal plants are much less able to respond to sudden changes in electrical demand, potentially causing frequency and Voltage instability. Pumped storage plants, like other hydroelectric plants, can respond to load changes within seconds. The first use of pumped storage was in the 1890s in Italy and Switzerland . In the 1930s reversible hydroelectric turbines became available. These turbines could operate as both turbine-generators and in reverse as electric motor driven pumps. The latest in large-scale engineering technology are variable speed machines for greater efficiency. These machines generate in Synchronisation with the network frequency, but operate Asynchronously (independent of the network frequency) as motor-pumps. A new use for pumped storage is to level the fluctuating output of Intermittent Power Sources . The pumped storage absorbs load at times of high output and low demand, while providing additional peak capacity. In certain jurisdictions, Electricity Prices may be close to zero or occasionally negative ( Ontario in early September, 2006), indicating there is more generation than load available to absorb it; although at present this is rarely due to Wind alone, increased wind generation may increase the likelihood of such occurrences. It is particularly likely that pumped storage will become especially important as a balance for very large scale Photovoltaic generation.http://www.iea-pvps.org/products/rep8_02s.htm In 2000 the United States had 19.5 GW of pumped storage capacity, accounting for 2.5% of baseload generating capacity. PHS generated (net) -5.5 GWh of energyhttp://www.eia.doe.gov/emeu/aer/pdf/pages/sec8_8.pdf because more energy is consumed in pumping than is generated; losses occur due to water evaporation, electric turbine/pump efficiency, and friction. In 1999 the EU had 32 GW capacity of pumped storage out of a total of 188 GW of hydropower and representing 5.5% of total electrical capacity in the EU. POTENTIAL TECHNOLOGIES The use of underground reservoirs as lower dams has been investigated. Salt Mine s could be used, although ongoing and unwanted dissolution of salt could be a problem. If they prove affordable, underground systems could greatly expand the number of pumped storage sites. Saturated Brine is substantially heavier than fresh water or seawater. A new concept in pumped-storage is utilising wind energy to pump water. A setup of wind turbines that direct drive water pumps or an 'Energy Storing Wind Dam' can make this a more efficient process. WORLDWIDE LIST OF PUMPED STORAGE PLANTS Australia
Austria
Belgium
Bulgaria
Canada
China Croatia
Czech Republic
France
Germany
India
Iran Ireland
Italy
Japan
Lithuania
Luxembourg
Norway Note that Norway has a high density of hydroelectric power generation, so some of the following locations are simply pumps that never generate power themselves, but transfer water to reservoirs where it can be re-used by existing hydroelectric power stations. This information comes from [http://www.mika.no/Nygaard%20pumpekraftverk.htm , and [http://www.miljostatus.no/aust-agder/tema/vann/vassdrag/vassdragsregulering/kraftverk.htm]
Philippines
Poland
Portugal
Russia
Serbia
Slovakia
Slovenija
South Africa
Spain
Sweden
Taiwan Ukraine
United Kingdom
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REFERENCES SEE ALSO
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