Compressed Air Energy Storage
Compressed air energy storage (CAES) is really a hybrid storage/power production system. Off-peak electricity is used to power a motor/generator that drives compressors to force air into an underground storage reservoir, such as a rock cavern or abandoned mine. When the demand for electric power peaks, the process is reversed. The compressed air is returned to the surface, and is fed into an industrial gas turbine, allowing the turbine to produce electricity more efficiently.
In traditional gas turbines, the air that drives the turbine is compressed and heated using natural gas. CAES technology needs less gas to produce power because it uses air that has already been compressed. There is only one CAES facility operating in the United States at present.