Liquid air ‘offers energy storage hope’

Turning air into liquid may offer a solution to one of the great challenges in engineering – how to store energy.

The Institution of Mechanical Engineers says liquid air can compete with batteries and hydrogen to store excess energy generated from renewables.

IMechE says “wrong-time” electricity generated by wind farms at night can be used to chill air to a cryogenic state at a distant location.

When demand increases, the liquid air can be warmed to drive a turbine.

Engineers say the process to produce “right-time” electricity can achieve an efficiency of up to 70%.

IMechE is holding a conference today to discuss new ideas on how using “cryo-power” can benefit the low-carbon economy.

The technology was originally developed by Peter Dearman, a garage inventor in Hertfordshire, to power vehicles.

A new firm, Highview Power Storage, was created to transfer Mr Dearman’s technology to a system that can store energy to be used on the power grid.

The process, part-funded by the government, has now been trialled for two years at the back of a power station in Slough, Berkshire.

More than hot air

The results have attracted the admiration of IMechE

“I get half a dozen people a week trying to persuade me they have a brilliant invention,” head of energy Tim Fox told BBC News.

“In this case, it is a very clever application that really does look like a potential solution to a really great challenge that faces us as we increase the amount of intermittent power from renewables.”

Dr Fox urged the government to provide incentives in its forthcoming electricity legislation for firms to store energy on a commercial scale with this and other technologies.

IMechE says the simplicity and elegance of the Highview process is appealing, especially as it addresses not just the problem of storage but also the separate problem of waste industrial heat.

The process follows a number of stages:

“Wrong-time electricity” is used to take in air, remove the CO2 and water vapour, which would otherwise freeze solid
the remaining air, mostly nitrogen, is chilled to -190C (-310F) and turns to liquid – this provides a compact storage medium that can later draw energy in the form of heat from the environment
the liquid air is held in a giant vacuum flask until it is needed
when demand for power rises, the liquid is warmed to ambient temperature. As it vapourises, the expanding gas drives a turbine to produce electricity – no combustion is involved

IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat that is currently vented and being released into the atmosphere.