UK firm plans to firm up liquid air energy storage

* Plans 7-10 MW facility to be operational in 2 years

* Small pilot plant tests successful

By Nina Chestney

LONDON, Feb 1 (Reuters) - UK company Highview Power Storage plans to develop a commercial facility which uses liquid air to store renewable energy after a pilot project was successful, the firm told Reuters on Wednesday.

One of the problems facing wind power development is how to store surplus energy when the wind is strong and release it when the weather is calm.

Highview recently completed tests at a 350 kilowatt pilot plant near London and connected it to the National Grid, and says it is confident its technology works and is planning a larger scale plant.

"We are currently in discussions to build a 7-10 megawatt unit. Our aim is for this to be operational in two years," said Toby Peters, the firm's co-founder and chief operating officer.

Liquid air energy storage takes electricity from the grid at peak times, such as on windy days, and uses it to cool air until it liquefies at minus 196 degrees Celsius.

The liquid air can then be stored cheaply and safely until it is needed and exposed to normal temperatures. Then the liquid immediately turns back into gas, expanding by 700 times, and can be used to turn a turbine and feed electricity back to the grid.