Main Page | See live article | Alphabetical index

Pumped storage hydroelectricity

Pumped storage hydroelectricity is a method of storing and producing electricity to supply high peak demands. At times of low electrical demand, excess electrical capacity is used to pump water into an elevated reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine, generating hydroelectricity. About 70% 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 natural height difference between two natural bodies of water or artificial reservoirs.

The water of Llyn Stwlan, the upper reservoir of the Ffestiniog Pumped Storage Scheme in north Wales, can just be glimpsed on the right. The lower power station has four water turbines which can 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.

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 capacity, while reducing the need to build special power plants which run only at peak demand times using expensive natural gas. Modern turbines in the pumped water plants can be brought up to full power in a matter of seconds to respond to demand.

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


United Kingdom United States Other