Pumped-storage Hydroelectricity

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 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). 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.

Due to evaporation losses from the exposed water surface and mechanical efficiency losses during conversion 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 power available to date.

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 is economical because 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 those 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 concept is wind-pumped water storage where vagaries of Wind Power can be leveled by using the wind power to fill a reservoir and generate grid power from the reservoir turbines.

In 2000 the United States had 19.5 GW capacity of pumped storage. This produced a net -5.5 GW of power because they consume more power filling their reservoirs than they generate by emptying them.

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