Optimization of dynamic compressed CO2 energy storage system: The role of supercritical fluid properties

The rising demand for efficient energy storage has spurred the development of technologies like liquefied CO2 energy storage systems, which reduce pressure fluctuations by storing CO2 as a liquid. Traditionally, the storage temperature of CO2 is the saturation liquid temperature because evaporation compensation helps maintain stable pressure during gas release. However, the liquefied CO2 energy storage system suffers low round-trip efficiency due to low temperature for liquefaction. Here, we propose a compressed CO2 energy storage (CCES) system using the properties of supercritical fluids to extend the discharging time. The core optimization strategy involves storing sCO2 near the pseudo-critical temperature during the charging process, which facilitates more efficient expansion of sCO2 during the discharging process, thereby extending the discharging time. Then, a dynamic CCES system incorporating three-stage compression and three-stage expansion are proposed. With the compression power consumption of 100 MW, the high-pressure tank is set to be 14.00 MPa and 7.50 MPa before and after discharging. Based on the discharging optimization method, the round-trip efficiency improves from 66.50 % to 69.32 %, and the discharging time extends from 0.96 h to 3 h. Our work fills the gap in the selection criteria for storage parameters of CCES system, and significantly improving the performance of CCES system.