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UK tests grid-linked 'liquid air' system for energy storage

UK start-up company Highview Power Storage (HPS) has completed a year-long trial of a grid-connected "liquid air" energy storage (LAES) system.

The company believes the system has the potential to solve the problem of storing surplus power generated by future large-scale renewable energy sources.

The 300kW pilot project is based at utility SSE’s 80MW biomass plant in Slough, southern England.

It cryogenically cools air to minus 196ºC – a concept already applied in liquid natural gas (LNG) transport – and stores it as a liquid in an insulated tank at atmospheric pressure.

When released and pumped-up to high pressure, then vapourised and heated to ambient temperature, the air expands to 700 times its liquid volume to drive a turbine.

This powers a generator to feed electricity to the grid. The cryogen is then evaporated and recycled to give the system a round-trip efficiency of around 50%.

The Slough LAES system, which was part-funded by a £1.1m grant from the UK Department of Energy and Climate Change (DECC), has a 2.5MWh storage capacity. But HPS believe the technology can be scaled up to a 50MW-plus system with over four hours of storage capability.

“Whereas many companies were focusing on fast-response but relatively small-scale battery technologies, we started out five years ago to develop a system which could deliver affordable, long-duration, large-scale energy storage,” says HPS chief operating officer Toby Peters. “We identified this as the big gap in the market.”

Peters claims other energy storage solutions under development “are proving insufficient”.

“Lithium ion batteries cannot be scaled up to hold large amounts of energy, while pumped-hydro storage needs mountains nearby and billions of litres of water to be viable,” notes Peters.

"The LAES system can store a similar amount as a medium-sized pumped-hydro plant and has no geographical constraints.”

HPS is currently working with partners in South Africa and China, as well as the UK and elsewhere in Europe, to develop large-scale LAES projects.

Tim Fox, head of energy at the UK's Institution of Mechanical Engineers, which hosted the first public presentation of LAES, says: “Liquid air energy storage is a very promising technology, using our most abundant resource to solve one of the renewable energy industry’s most pressing challenges."