Pumped-storage hydroelectricity

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Hydro-storage redirects here. For storage of water for other purposes, see Reservoir.
Diagram of the TVA pumped storage facility at Raccoon Mountain Pumped-Storage Plant
Power distribution, over a day, of a pumped-storage hydroelectricity facility. Green represents power consumed in pumping; red is power generated.

Pumped storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. Pumped storage is the largest-capacity form of grid energy storage now available.


[edit] 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.[1] 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 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 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 plants and renewable energy power plants that provide base-load electricity to continue operating at peak efficiency (Base load power plants), 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 upper reservoir (Llyn Stwlan) and dam of the Ffestiniog Pumped Storage Scheme in north Wales. The lower power station has four water turbines which generate 360 MW of electricity within 60 seconds of the need arising. The size of the dam can be judged from the car parked below.

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.[2]

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 energy[3] 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.

[edit] Potential technologies

The use of underground reservoirs as lower dams has been investigated. Salt mines could be used, although ongoing and unwanted dissolution of salt could be a problem. If they prove affordable, underground systems might greatly expand the number of pumped storage sites. Saturated brine is about 20% denser than fresh water.

A new concept in pumped storage is to utilise wind turbines or solar power to drive water pumps directly, in effect an 'Energy Storing Wind or Solar Dam'. This could provide a more efficient process and usefully smooth out the variabilities of energy captured from the wind or sun [4] [5].

One can use pumped sea water to store the energy . A potential example of this could be used in a tidal barrage or tidal lagoon . A potential benefit of this arises if seawater is pumped behind the barrage or into the lagoon at high tide when the water level is roughly equal either side of the barrier , when the potential energy difference is close to zero . Then water is released at low tide when a head of water has has been built up behind the barrier , when there is a far greater potential energy difference between the two bodies of water . The result being that when the energy used to pump the water is recovered , it will have multiplied to a degree depending on the head of water built up .[3]

[edit] Worldwide list of pumped storage plants

  • Rio Grande-Cerro Pelado Hydroelectric Complex (1986), 750 MW
  • Häusling (1988), 360 MW
  • Lünerseewerk (1958), 232 MW
  • Kraftwerksgruppe Fragant, 100 MW
  • Kühtai (1981), 250 MW
  • Malta-Hauptstufe (1979), 730 MW
  • Rodundwerk I (1952), 198 MW
  • Rodundwerk II (1976), 276 MW
  • Roßhag (1972), 231 MW
  • Silz (1981), 500 MW
  • Coo (1979), 1100 MW
  • Plate Taille (1981), 136 MW
  • PAVEC Belmeken (197?), 375 MW
  • PAVEC Chaira (1998), 864 MW
  • Guangzhou (2000), 2,400 MW
  • Tianhuangping (2001), 1,800 MW
  • CHE Fužine (1957). 4.6 MW
  • RHE Lepenica (1985), 1.14/1.25 MW[6]
  • RHE Velebit (1984), 276/240MW[7]
Czech Republic
  • Grand Maison (1997), 1,070 MW
  • La Coche (1976), 285 MW
  • Le Cheylas (1979), 485 MW
  • Montézic (1983), 920 MW
  • Rance (1966), 240 MW hybrid pumped water-tidal plant
  • Revin (1976), 800 MW
  • Super Bissorte (1978), 720 MW
  • Erzhausen (1964), 220 MW
  • Geesthacht (Hamburg) (1958), 120 MW
  • Goldisthal (2002), 1,060 MW
  • Happurg (1958), 160 MW
  • Hohenwarte II (1966), 320 MW
  • Koepchenwerk (1989), 153 MW
  • Langenprozelten (1976), 160 MW
  • Markersbach (1981), 1,050 MW
  • Niederwartha, Dresden (1958), 120 MW
  • Waldeck II (1973), 440 MW
  • Bhira, Maharashtra, 150 MW
  • Kadamparai, Coimbatore, Tamil Nadu, 400 MW (4 x 100 MW)
  • Nagarjuna Sagar PH, Andhra Pradesh, 810 MW (1 x 110 MW + 7 x 100 MW)
  • Purulia Pumped Storage Project, Ayodhya Hills, Purulia, West Bengal, 900 MW
  • Srisailam Left Bank PH, Andhra Pradesh, 900 MW (6 x 150 MW)
  • Tehri Dam, Uttranchal , 1,000 MW
  • Siah Bisheh, Iran (1996), 1,140 MW
  • Chiotas (1981), 1,184 MW
  • Lago Delio (1971), 1,040 MW
  • Piastra Edolo (1982), 1,020 MW
  • Presenzano (1992), 1,000 MW
  • Imaichi (1991), 1,050 MW
  • Kannagawa (2005), 2,700 MW
  • Kazunogawa (2001), 1,600 MW
  • Kisenyama, 466 MW
  • Matanoagawa (1999), 1,200 MW
  • Midono, 122 MW
  • Niikappu, 200 MW
  • Okawachi (1995), 1,280 MW
  • Okutataragi (1998), 1,932 MW
  • Okuyoshino, 1,206 MW
  • Shin-Takasegawa, 1,280 MW
  • Shiobara, 900 MW
  • Takami, 200 MW
  • Tamahara (1986), 1,200 MW
  • Yagisawa, 240 MW
  • Yanbaru, Okinawa (1999), 30 MW (First high-head seawater pumped storage in the world) Hitachi
  • Vianden (1964), 1,100 MW

Note: Norway has many large hydroelectric power stations. At some of the locations listed below, no power is generated: the pumps move water up to reservoirs feeding conventional hydroelectric power stations. [8][9][10]

  • Aurland III (1979), 270 MW
  • Jukla, 40 MW
  • Kastdalen
  • Nygard, Modalen
  • Skjeggedal
Møre og Romsdal
  • Mardal
  • Monge
  • Tverrvatn
  • Duge
  • Hjorteland
  • Hunnevatn
  • Saurdal, 640 MW
  • Stølsdal, 17 MW
  • CBK, 700 MW
  • Dychów, 79.5 MW
  • Niedzica, 92.6 MW
  • Porąbka-Żar, 500 MW
  • Solina, 200 MW
  • Żarnowiec, 716 MW
  • Żydowo, 150 MW
  • Aguieira, 270 MW
  • Alqueva, 260 MW
  • Alto Rabagão, 72 MW
  • Torrão, 144 MW
  • Vilarinho II, 74 MW
  • Kuban (1968), 15.9/19.2 MW
  • Zagorsk (1994), 1,200/1,320 MW
  • Zelenchuk (under construction), 140/150.6 MW
  • Bajina Basta (1982), 614 MW
Slovakia [4]
  • Čierny Váh, 735.16 MW
  • Liptovská Mara, 198 MW
  • Ružín, 60 MW
  • Dobšiná, 24 MW
  • Avče, 180 MW
South Africa [5]
  • Aguayo (Cantabria), 339 MW
  • Aldeadavila (Salamanca), 422 MW (2 X 211 MW) [6]
  • Moralets-Llauset (Lleida/Huesca), 210 MW [7]
  • La Muela (Valencia), 628 MW
  • Sallente-Estany Gento (Lleida), 451 MW [8]
  • Tajo de la Encantada (Málaga), 360 MW
  • Tavascan-Montmara (Lleida), 52 MW
  • Villarino (Salamanca), 810 MW (6 X 135 MW) [9]
  • Juktan, 334 MW [11]
  • Cleuson-Dixence VS, Lac des Dix, 2,099 MW (turbine)
  • Guttannen BE / Grimsel 2 (Kraftwerke Oberhasli), Grimselsee, 1070 MW (turbine)
  • Peccia, Cavergno, Verbano, Bavona, Altstafel, Robiei TI (Maggia Kraftwerke AG), 620 MW (turbine)
  • Hongrin VD, Lac de l'Hongrin, 240 MW installed, 420 MW planned
  • Mapragg SG, Stausee Mapragg (Kraftwerke Sarganserland), 370 MW (turbine)
  • Linthal GL, Linth-Limmern, 340 MW turbine installed; 1000 MW planned pump and turbine by 2015
  • Altendorf SZ / Einsiedeln, Sihlsee, 340 cubic meters per second
  • Lobbia GR (EW der Stadt Zürich), 37 MW (pump)
  • Ova Spin GR (Engadiner Kraftwerke AG), 47 MW (pump)
  • Ferrera GR, Valle di Lei, 82 MW (pump)
  • Minghu (1985) 1,000 MW
  • Mingtan (1994) 1,620 MW
  • Dniestr HPSP, 972 MW installed, 2,268 MW planned photo
  • Kaniv HPSP (design stage), 1800 MW [10]
  • Kyiv HPSP, 235.5 MW [11]
  • Tashlyk HPSP, 905 MW/-1325 MW [12]
United Kingdom
United States
  • Castaic Dam (1978), 1,566 MW
  • Edward C. Hyatt (1968), 780 MW
  • Helms (1984), 1,200 MW
  • Iowa Hill, (Proposed 2010), 400 MW [13]
  • John S. Eastwood (1988), 200 MW
  • Pyramid Lake (1973), 1,495 MW
  • San Luis Dam (William R. Gianelli) (1968), 424 MW
  • Rocky River (1929), 31 MW
  • Rocky Mountain Pumped Storage Station, 848 MW
  • Wallace Dam, Lake Oconee/Lake Sinclair, 4 x 52 MW reversible units - operated by Georgia Power
  • Koko Crater, Oahu, Hawaii (Proposed)
  • Clarence Cannon dam (1983), 58 MW (pump-back capability tested twice in 1984 and not used since.[14])
  • Taum Sauk, 450 MW (pure pump-back; out of operation as of December, 2005)
New Jersey
  • Mt. Hope, 2,000 MW[12]
  • Yards Creek Generating Station (1965), 400 MW [15]
New York
  • Salina Pumped Storage (Grand River Dam Authority) (1971), 260MW
South Carolina

[edit] References

[edit] See also

[edit] External links

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