Storing solar and wind energy in cold liquid air

New Scientist : A UK company, Highview Power Storage, has been running a pilot plant designed to store potential energy in the form of liquid air. Solar- and wind-powered generators of electricity, which are growing in number, need some kind of reservoir to store the excess power generated for use when the Sun isn’t shining or the wind isn’t blowing. The new process stores excess energy by using it to cool air to around -190 °C; the resulting liquid air, or cryogen, is then stored in a tank at ambient pressure. When electricity is needed, the cryogen is subjected to pressure and heat, which produces a high-pressure gas that drives a turbine. So far, the process recovers about 50% of the electricity that is fed in, and the company plans to build a 3.5-MW system by late 2012.