Geophysics: Lenses form bad vibrations

Abstract

A new type of "regenerative" fuel cell could revolutionize the energy industry by making electricity as easy to store as oil. Most fuel cells generate electricity by combining hydrogen and oxygen, with water as the only by-product, whereas the regenerative fuel cell stores energy in tanks of salt solution. Work on this kind of fuel cell is being earned out by Innogy, which is currently part of National Power in die UK but is due to be demerged soon.By allowing electricity to be stockpiled, Innogy's Regenesys system will let smallscale generators compete with large centralized plants. "We like to think of this as an electricity warehouse rather than a giantrechargeable batter)'," said David Trelfall, director of the project. 'Just like a warehouse it will allow generators to put electricity in when the prices are cheap and to sell it again when the prices are high."Regenesys uses sodium bromide and sodium polysulphide salts, which are abundant and safe. A reversible elecoochemical reaction stores energy in the salts, which are separated by a proton exchange membrane. The electrodes play no part in the reaction, unlike a batter)', where the size and shape of the electrodes limit the performance.