Pumped-storage hydroelectricity

From Academic Kids

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Diagram of the TVA pumped storage facility at Racoon Mountain

Pumped storage hydroelectricity is a method of storing and producing electricity to supply high peak demands by moving water between reservoirs at different elevations.

Contents

Overview

At times of low electrical demand, excess electrical 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 hydroelectricity. Reversible turbine/generator assemblies act as pump and turbine (usually a francis turbine design). Between 70% and 85% of the electrical energy used to pump the water into the elevated reservoir can be regained in this process. Some facilities use abandoned mines as the lower reservoir, but many use the height difference between two natural bodies of water or artificial reservoirs.

This system is economical as it flattens out the variations in the load 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 their most efficient capacity, while reducing the need to build special power plants which run only at peak demand times using more costly generation methods.

As well as energy management, pumped storage systems are important components in controlling electrical network frequency and in provision of reserve generation. Thermal plants are much less able to respond to sudden changes in electrical demand, which cause frequency and voltage instability. Pumped storage plants, in common with other hydroelectric plants, can respond to these 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.
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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 concept is wind-pumped water storage where vagaries in wind power can be leveled by using the wind power to fill a reservoir and generating grid power from the reservoir turbines.

In 2000 the United States had 19500 MWe capacity of pumped storage. This produced a net -5500 MWe of power because they consume more power filling their reservoirs than they generate by emptying them. Still the technique is considered a worthwhile addition to the electrical grid as the most cost effective means to date for storage of mass amounts of electrical power.

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.

Worldwide list of pumped storage plants

Australia

Canada

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

China

Czech Republic

Germany

Ireland

Italy

France

Japan

Poland

Russia

South Africa

Taiwan

United Kingdom

United States

Other

Salt water (ocean)

  • Kunigami Village, Okinawa, Japan [3] (http://www.jcold.or.jp/Eng/Seawater/Seawater.htm)[4] (http://www.hitachi.com/rev/1998/revoct98/r4_108.pdf)
  • Koko Crater, Oahu, Hawaii [5] (http://www.hawaii.gov/dbedt/ert/pshpps/pshpps.html) (Proposed)

See also

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Wikipedia Energy Directory

External links

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