UK: Refrigeration has a pivotal role in a technology which could provide an answer to the problem of large-scale storage of renewable energy.
It is well known that a large scale means of storing renewable energy is an absolute necessity for the future success of the low carbon grid With our dash for green electricity, the deployment of wind farms has already outstripped the ability of many grids throughout the world to integrate this intermittent source of energy.

While batteries are viable for small scale energy balancing, historically pumped hydro has been employed as the solution for large-scale storage. However, this technology is limited by geographical contraints and its needs for billions of litres of water, making it unfeasible in many instances.

UK company, Highview Power Storage, has developed and built a pilot plant using liquefied air or liquid nitrogen (78% of air) as the storage medium.

Highview's approach extracts carbon dioxide and water vapour out of the air and then super-chills it using wind, solar or other renewable power to its liquid state (-196C).

Liquefied air has a high expansion ratio between its liquid state and, more common, gaseous state, expanding about 700 times when regasified. As with a traditional steam engine, a cryogenic engine relies on phase-change (liquid to gas) and expansion within a confined space, eg engine cylinder or turbine.

Highview has now built a fully operational 300kW, 2.5MWh, pilot plant which was part-funded by a £1.1m grant from the UK Government's Department of Energy and Climate Change, is connected to the UK's national grid; as such it complies with all the necessary regulations and inspections (just like any other commercial generator). The plant, the first LAES plant in the world, is hosted by SSE (Scottish & Southern Energy) at their Slough Heat & Power 80MW biomass plant.

Critically, the system can be scaled to 100MWs/GWhs of storage, similar to a medium scale pumped hydro. But, liquid air can easily be stored in the same low pressure tanks as used by the LNG industry - it is hundreds of times more energy dense than water (therefore taking up far less space) - and the process does not need large mountains or lakes.

The company is currently in advanced discussion with commercial partners around the deployment of a fully funded first commercial reference plant.