Thermodynamic characteristics of a novel supercritical compressed air energy storage system

• A novel supercritical compressed air energy storage system is proposed.
• The energy density of SC-CAES is approximately 18 times larger than that of conventional CAES.
• The characteristic of thermodynamics and exergy destruction is comprehensively analysed.
• The corresponding optimum relationship between charging and discharging pressure is illustrated.
• A turning point of efficiency is indicated because of the heat transfer of crossing the critical point.

A novel supercritical compressed air energy storage (SC-CAES) system is proposed by our team to solve the problems of conventional CAES. The system eliminates the dependence on fossil fuel and large gas-storage cavern, as well as possesses the advantages of high efficiency by employing the special properties of supercritical air, which is significant for the development of electrical energy storage. The thermodynamic model of the SC-CAES system is built, and the thermodynamic characters are revealed. Through the exergy analysis of the system, the processes of the larger exergy destruction include compression, expansion, cold storage/heat exchange and throttle. Furthermore, sensitivity analysis shows that there is an optimal energy releasing pressure to make the system achieve the highest efficiency when energy storage pressure is constant. The efficiency of SC-CAES is expected to reach about 67.41% when energy storage pressure and energy releasing pressure are 120 bar and 95.01 bar, respectively. At the same time, the energy density is 18 times larger than that of conventional CAES. Sensitivity analysis also shows the change laws of system efficiency varying with other basic system parameters. The study provides support for the design and engineering of SC-CAES.