Liquid Air Stores Renewable Energy

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Renewable sources of energy such as wind and solar power are intermittent. The wind doesn't always blow; the sun doesn't always shine. But power grids need uninterrupted, reliable flows of energy in order to guarantee electricity to masses. If renewable energy is to come online with coal and natural gas, it can't be sporadic. That means it needs to be efficiently stored so it can be utilized on cloudy, windless days and at night.

Britain's Highview Power Storage has developed an unusual way to store energy generated by wind and sunlight: liquid air. Sound cool? It is, quite literally.

The company's CryoEnergy System uses excess energy to run refrigeration units that cool air down to a chilly -320.8 Fahrenheit, where it liquefies. The liquified air can be stored in an insulated tank at a low pressure.

During periods of high-demand on the power grid, the liquified air can be released into a confined space, where it is warmed to just above -320.8 F. At that temperature, the air becomes gas, which is used to spin a turbine to produce electricity.

Only 50 percent of the energy that went into cooling the air is returned when exposed to ambient air temperatures. However, if exposed to heated air, the phase change from liquid to gas is more intense, and produces an efficiency of 70 percent.

That efficiency percentage could be boosted if the system were installed in a facility where heat waste already existed and could be used to run the refrigeration.

Other systems designed to store energy from renewable sources include pumped hydro, where excess energy is used to pump water into a reservoir located at a higher elevation. When power is needed, the water is allowed to flow down over a dam where it spins turbines that generate electricity. According to an article in Gizmag, pumped hydro infrastructure is more expensive to build and not as portable as the CryoEnergy System. Another way to store energy is in batteries. But they typically cost about $4,000 per kilowatt of generating capacity, while the CES costs about $1,000 per kilowatt.

And because the only by-product of CES is cold air, the technology could potentially be used to provide refrigeration or air conditioning.

According to CleanTechnica, a pilot projest has been running in Scotland for the last nine months. Highview has plans to build a 3.5 MW, commercial-scale system by late 2012 and an 8 MW to 10 MW storage plant by early 2014.

Image: Highview Power Storage

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