Thermodynamic analysis of an open type isothermal compressed air energy storage system based on hydraulic pump/turbine and spray cooling

•A novel open type I-CAES with hydraulic machine and spray cooling is proposed.•A transient thermodynamic model including air-water heat transfer is presented.•OI-CAES enables continuous energy storage and near isothermal compression.•Indicated efficiency of 98% and roundtrip efficiency of 76% are achieved.•Compression and expansion time ratio of 99% and 96% are obtained.