Highview Power Storage is a London-based startup developing a frozen air (or "liquid air") technology for grid-scale storage applications.
Many interesting grid-scale storage technologies have cropped up in recent years including liquid batteries, compressed air storage, storage through electric vehicles, lithion ion - and the need is clear: if we want successful integration of intermittent renewables (ie. solar, wind) in grid infrastructure, energy storage is a key component -- as well as a major challenge, as we've already discussed.
The 'frozen air' energy process begins during off-peak hours, when electricity generated by renewables is used to cool air down to -310F, turning the air from gas to liquid. The croygenic 'liquid air' is stored in a vacuum tank, and when electricity demand grows, the liquid air is warmed to ambient temperature, and the resulting increase in pressure drives a turbine for generating electricity.
Highview has built and successfully operated a pilot at the Slough Heat & Power station since 2010, and they expect to build commercial-scale projects in the upcoming year.
Highview admits that the current process is only about 25% efficient, but once systems are produced at scale, the conversion could be up to 70% efficient.