Wind farms simply aren't reliable sources of steady power, which is why many rely on enormous battery systems to store excess current for times when the wind isn't gusting enough to meet our energy demands. But the production of these batteries is itself a drain on resources. So what if — instead of lithium and metal hydride batteries — wind farms could just store energy using the same air that spins the propellers?
It's called Liquid Air Storage, a process developed by Peter Dearman, a Hertfordshire garage inventor and head of The Dearman Engine Company, initially to power electric vehicles. With the realisation that the technology could be used for green energy storage, Dearman created a new company, Highview Power Storage, to further develop the technology in conjunction with the UK government. A test system has been successfully trialled at the Berkshire power station for the past two years.
The HPS system relies on "wrong-time" electricity — the stuff produced when demand is low, like at night. A portion of this energy runs chillers that first suck in ambient air. The chillers remove any CO2 and water vapour, then freeze the remaining gas (mostly nitrogen) to a cryogenic state at -190C. At this temperature, the nitrogen reverts to a liquid form. This is the actual energy sequestration process. Then it must be stored in specially insulated flasks.
When energy demands outpace the power currently being generated, these flasks can be attached to turbines, opened and heated. The rapid expansion of Nitrogen from a liquid to gaseous state generates tremendous pressure to spin the turbine. What's more, adjusting the amount of heat applied to the tank moderates the speed of the expanding gas without the need for complicated control systems. HPS systems representatives estimate the cost per kilowatt could be as low as $US1000.
While the current prototype is only about 25 per cent efficient, coupling these devices to a waste heat source (even the heat exchanger on the tank's own chiller) can boost its efficiency as high as 70 per cent. Plus, these systems can be built now, using widely available parts. They can last up to 20 years, whereas a conventional battery's average lifespan of just five.
"Batteries can get 80 per cent efficiency, so this isn't as good in that respect," the Institution of Mechanical Engineers Head of Energy and Environment, Dr Tim Fox, told BBC News. "But we do not have a battery industry in the UK, and we do have plenty of respected engineers to produce a technology like this. What's more, it uses standard industrial components, which reduces commercial risk. It will last for decades and it can be fixed with a spanner." [Cleantechnica - BBC News - PlayItBack - Liquid Air - Highview Power]