Yesterday's announcement by Denver-based Dakota Salts of a proposed mining and wind energy storage project in northwestern North Dakota may be met with skepticism by those familiar with wind storage technology. To date, there are only two working projects using compressed air to store energy, one in Germany and the other in Alabama. Neither of these projects uses wind as the primary source of power. A third project of this type, which is wind-based, is under consideration in Iowa but is not expected to be operational until 2011.
One reason cited for the limited use of the technology proposed by Dakota Salts (often referred to as Compressed Air Energy Storage or CAES) is its inefficiency. A 2008 MSNBC article points out that the energy required for heat management is the primary reason why CAES technology is not more widely used in commercial applications.
According to the MSNBC article, the CAES process uses off-peak electricity to compress air, a process which also raises the air's temperature to a level too high (roughly 1,100 F.) to be pumped underground. The air is therefore cooled to around 120 F. before it is stored.
In order to turn a turbine, the air must be reheated before it is released, usually by natural gas. This energy overhead reduces efficiency by about 50%, according to the MSNBC article.
The article goes on to describe a new process under development that stores the heat when it's removed during the initial air compression process. The stored heat then is used to raise the discharged air to the temperature required to turn a turbine. Researchers expect a prototype of this technology to be available by 2012.
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