The New Way to Store Energy?

Published: 12 Mar 2013

Renewable energy sources such as wind, sun, and tides are affected by ‘natural rhythms’ that are frequently out of step with our own demands for power, meaning that energy is not always produced when it’s wanted. If this ‘wrong time’ energy is not to be wasted, it has to be stored.

One way to do this is with batteries, or using hydrogen, but now liquid air is being put forward as a viable alternative to both, and it’s being taken seriously.

Research is already being funded by the government, with the technology having been on trial now for two years at a power station in Slough.

Liquid air technology as a concept was originally developed for use in vehicles by Peter Dearman. He began his career as ‘a garage inventor’ as a teenager fifty years ago, because he believed there wouldn’t be enough raw materials in the future for everyone in the world to have a car. Now liquid air offers up a way in which to capture and store ‘wrong time’ energy - energy that’s created when it’s not needed.

This is how the liquid air energy storage process would work at night.

Instead of just wasting excess energy when demand is low, liquid air plants at wind farms could take in air and remove the CO2 and water vapour from it. This would leave behind mostly nitrogen that could then be chilled to -190C (-310F), at which point the air would become liquid, creating a compact storage medium that could be held and kept cold in a giant vacuum flask.

When demand for energy increased the next day, the liquid air could be warmed to ambient temperature. As it vaporises, it would expand, and it’s this expansion that would be used to drive a turbine to produce electricity.

Currently the process is only about 25% efficient. But this could be greatly improved if cryo-generators, used to produce low temperatures, were sited in tandem with power stations. Then the low grade heat they generate and which is currently just vented could be used as an integral part of the process to boost the speed of thermal expansion of the liquid air.

It’s possible to save even more energy by taking waste cool air from the initial chilling process and sending it through large gravel filled tanks. The gravel captures that cold, which can then be used to restart the air-chilling the next evening in a simple and elegant process.

In time it is thought that around 75% efficiency in terms of energy storage could be achieved using liquid air technology. Perhaps not the 80% of batteries, but still significant and with the added benefit that this is technology that uses standard industrial components. For those who choose to invest in such a system there is little commercial risk because the technology is known to be robust long-term. What’s more, should anything go wrong, it can easily be fixed with just a spanner.


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