Liquid air 'offers energy storage hope'  

The BBS has an article on a form of energy storage being trialled in the UK - 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 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%. ...

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, Buckinghamshire. ...

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 (these would freeze otherwise)
* the remaining air, mostly nitrogen, is chilled to -190C (-310F) and turns to liquid (changing the state of the air from gas to liquid is what stores the energy) 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 vaporizes, it 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. The heat can be used to boost the thermal expansion of the liquid air.

More energy is saved by taking the waste cool air when the air has finished chilling, and passing it through three tanks containing gravel. The chilled gravel stores the coolness until it is needed to restart the air-chilling process.