October 15, 2008

The return of compressed air energy storage

Sonal Patel

Faced with soaring energy prices, researchers and developers worldwide are giving compressed air energy storage (CAES)—a technology almost 50 years old—a dusting, a spit shine, and a new life. In particular, they see it as a critical component for the dispatch of wind and other renewable power.

The technology, which involves storing off-peak-generated energy in the form of compressed air, usually in an underground reservoir, can trace its roots to the early 1960s, when the evaluation of gas turbine technology for power production began. It gained momentum during the next decade because of its promising thermal efficiency and response capabilities for providing load-following and peaking power support.

But since the commissioning of the only two existing CAES plants in the world—the 290-MW Huntorf plant in north Germany in 1978 and the 110-MW Alabama Electric Corp. plant in McIntosh, Ala., in 1991—CAES developments have been rare.

One reason for this is that setting up a CAES facility is pricey and requires finding a geologic formation that can support it. For example, both the German and Alabama plants store compressed air in mined salt caverns

CAES plants work like big batteries. Electric motors drive compressors that compress air (at perhaps 1,100 psi) into an underground geologic formation during off-peak hours. When the electricity is needed most, the precompressed air (essentially replacing the compressor in a traditional combustion turbine) is used in modified combustion turbines to generate electricity (Figure 1). Natural gas or other fossil fuels are still required to run the turbines, but the process is more efficient—using up to 50% less natural gas than standard production, according to Sandia National Laboratories.

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