Pumped-storage hydroelectricity

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Diagram of the TVA pumped storage facility at Raccoon Mountain Pumped-Storage Plant
Power spectrum of a pumped-storage hydroelectricity. Green represents power consumed in pumping; red is power generated.

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 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 that provide base-load electricity to continue operating at peak efficiency 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.

File:Stwlan.dam.750pix.jpg
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 wind powered generators. 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, wind may increase the likelihood of such occurrences.

In 2000 the United States had 19.5 GWh of pumped storage capacity. This produced a net -5.5 GWh of energy because they consume more energy filling their reservoirs than they generate by emptying them, implying a 78% efficiency ratio (power recovered / power input).

In 1999 the EU had 32 GWh capacity of pumped storage out of a total of 188 GWh 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 mines 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 pump-generator located on the bottom of a lake or the ocean could facilitate water transit between a floating or shoreline reservoir and a deep water storage bladder. This option may not be feasible.

Worldwide list of pumped storage plants

Australia

Austria

  • 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

Belgium

  • Coo, (1979), 1100 MW

Bulgaria

  • PAVEC Chaira, (1998),800 MW

Canada

  • Sir Adam Beck Pump Generating Station, (1957) near Niagara Falls, reversible Deriaz turbines, 174 MW

China

  • Guangzhou, (2000), 2,400 MW
  • Tianhuangping (2001), 1,800 MW

Czech Republic

France

  • Grand Maison (1997), 1,070 MW
  • La Coche, 285 MW
  • Le Cheylas, 485 MW
  • Montézic, 920 MW
  • Rance, 240 MW hybrid pumped water-tidal plant
  • Revin, 800 MW
  • Super Bissorte, 720 MW

Germany

  • 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

Iran

Ireland

Italy

  • Piastra Edolo (1982), 1,020 MW
  • Chiotas (1981), 1,184 MW
  • Presenzano (1992), 1,000 MW
  • Lago Delio (1971), 1,040 MW

Japan

  • 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 (1999), 30 MW

Lithuania

Luxembourg

  • Vianden, (1964), 1,100 MW

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 [1], [2], and [3]

Philippines

  • CBK, 700MW

Poland

  • Żarnowiec, 716 MW
  • Porąbka-Żar, 500 MW
  • Solina, 200 MW
  • Żydowo, 150 MW
  • Niedzica, 92.6 MW
  • Dychów, 79.5 MW

Portugal

  • Aguieira, 270MW
  • Alqueva, 260MW
  • Alto Rabagão, 72MW
  • Torrão, 144MW
  • Vilarinho II, 74MW

Russia

  • Zagorsk (1994) 1,200 MW

Serbia

  • Bajina Basta (1966) 364 MW

Slovakia

  • Čierny Váh 735.16 MW

South Africa

Spain

  • La Muela (Valencia) 628 MW
  • Sallente-Estany Gento (Lleida) 451 MW [4]
  • Tajo de la Encantada (Málaga) 360 MW
  • Aguayo (Cantabria) 339 MW
  • Moralets-Llauset (Lleida/Huesca) 210 MW [5]
  • Tavascan-Montmara (Lleida) 52 MW

Sweden

  • Juktan, 334 MW [1]

Taiwan

  • Minghu (1985) 1,000 MW
  • Mingtan (1994) 1,620 MW

Ukraine

  • Kyiv HPSP 235.5 MW [6]
  • Tashlyk HPSP 905 MW/-1325 MW [7]
  • Dniestr HPSP (1st construction phase completed and now provides 972 MW, next phases will give up to 2,268 MW)[8]
  • Kaniv HPSP (design stage) 1800 MW [9]

United Kingdom

United States

Salt water (ocean)

  • Kunigami Village, Okinawa, Japan [12][13]
  • Koko Crater, Oahu, Hawaii (Proposed)

See also

External links

Articles about historical mechanical engineering landmarks from ASME:

  1. ^ http://hem.passagen.se/kts/english/turbin/francis/francis.htm
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