[0] Compressed Air Storage (CAES) [2] Gas used is about 40% of the amount used in comparable peaking turbine. First built in 1978. [3] 70% to 80% efficient; $30-$100 per kWh [1] 
Energy stored by compressing air into large underground caverns. Air combined with natural gas on exit and burned in turbine. The gas compensates for the cooling as air decompresses.