BBC: A two-year trial of a technology developed by a private inventor may provide an alternative to batteries for storing excess energy generated from renewable power sources. The technique, which has been tested at a power station in Slough, UK, uses electricity generated during nonpeak usage hours, such as overnight, to cryogenically liquefy air. When the power is needed, the liquid air is heated, causing it to vaporize and drive turbines, which generate extra electricity. Although the current facility has only a 25% efficiency rate, Tim Fox of the Institution of Mechanical Engineers says that harnessing excess heat from other industrial locations would simplify the warming process and could result in an efficiency of approximately 70%. And while that is lower than the efficiency of most batteries, Fox says that because the UK does not have a large battery industry, the new process would be a viable alternative for energy storage.