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

Abstract

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.