STORING HOT AIR

Compressed air energy storage: The natural option for Brayton Cycle CSP?
Helen Campbell, 27 June 2011 (CSP Today)

"While hugely efficient, compressed air energy storage in domal salt caverns is geographically limited in the US…[but] alternative formations could see… compressed air energy storage (CAES) …resolve [New Energy’s dispatchability] challenge…Energy produced off-peak from a renewable energy source or standard power plant is used to power air compressors that pump air into either pressurized storage tanks or underground caverns. When electricity is needed, the air is expanded via turbines, to generate energy. CAES saves renewable energy, quite literally, for a rainy day…

"Southwest Solar Technologies in the US, in partnership with Brayton Energy, has just [a few months ago] launched its pilot test for CAES and solar in Phoenix, Arizona, taking a dish-turbine approach and using a Brayton cycle turbine [with received air at 925° C.]…It’s a simple process, but the real issue is the geographic constraints, says John Crockett of the San Diego State University (SDSU) Research Foundation and part of a California Energy Commission-supported programme that provided funding for the Southwest/Brayton project."

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"…[It requires a reservoir structure, a rock formation, such as limestone, fractured shale, or a salt cavern]…[I]in the US, when you overlay a geological resources map, showing limestone or depleted oilfields, with a solar resource map, there aren’t that many places where they overlap.

"The other stumbling block for CAES, with solar or any other energy source, is the market penetration of renewables as a whole. Customers and producers will try to avoid paying for storage until they absolutely have to, and there is nothing irrational about that…When renewables penetration levels of 30% or higher [are achieved, the] market for power including storage [will be bigger]…Proven commerciality in other areas may impact positively on CAES’ applicability to solar…"

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"The only two existing power plants globally that already use CAES, one in Alabama and one in Germany, store the compressed air in domal salt caverns. Other projects in the US, in Iowa, California and New York are testing CAES in ‘alternative’ formations, including depleted gas reservoirs and aquifers…Paul Denholm, who leads analysis efforts on energy storage at the Department of Energy’s National Renewable Energy Laboratory (NREL), says success would mean a lot of potential for CAES…

"The success of CAES, emanating from any energy source, is also of high interest to the military, and is believed to already be used on a small scale to run such facilities as field communications centres…"