The round trip efficiency of compressed air for energy storage is greatly limited by the significant increase in the temperature of the compressed air (and the resulting heat loss) in high-ratio adiabatic compression. This paper introduces a multi-stage compression scheme with low-compression-ratio compressors and inter-compressor natural convection cooling resulting in a quasi-isothermal compression process that can be useful for large-scale energy storage. When many low pressure ratio compressors work inline, a high overall compression ratio can be achieved with high efficiency. The quasi-isothermally compressed air can then be expanded adiabatically in turbines to generate power with the addition of thermal energy, from either fuel or a solar thermal source. This paper presents mathematical models of such an energy storage system and discusses its round-trip performance with different operating schemes.

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