Solar-integrated trans-critical compressed CO2 energy storage system: A key solution for long-duration energy storage application

Conventional compressed carbon dioxide energy storage systems face performance limitations due to low expander inlet temperatures. Adding thermal energy through conventional fossil fuel combustion raises operational complexity and economic costs, with limited environmental advantages. This study introduces a trans-critical compressed carbon dioxide energy storage system that integrates solar energy, offering significant potential for development. Thermodynamic models of trans-critical compressed carbon dioxide energy storage system, incorporating distinct heat recovery sources (compression heat recovery and exhaust waste heat recovery), have been developed. Thermodynamic analyses were conducted using temperature-entropy diagrams. Under identical power consumption, the solar energy conversion efficiencies of systems are 21.22 % and 27.29 %. The round-trip efficiencies, at 81.86 % and 81.92 %, represent increases of 9.70 % and 9.76 % over conventional compressed carbon dioxide energy storage systems. Additionally, the electricity generation per unit volume of storage improved from 0.22 kWh/m3 to 0.38 kWh/m3. From a thermodynamic perspective, the trans-critical compressed carbon dioxide energy storage system utilizing exhaust waste heat recovery outperformed the system with compression heat recovery. Exergy analysis indicates that the established systems exhibit exergy efficiencies of 45.12 % and 51.75 %, respectively. The systems were further analyzed for exergy flow and exergy destruction, revealing that the trough solar collector is the primary source of exergy destruction in the solar thermal storage-equipped trans-critical compressed carbon dioxide energy storage system, accounting for 65.43 % and 59.03 %, respectively. In summary, the proposed system mitigates the limitations of renewable energy generation while enhancing operating parameters and efficiencies of the trans-critical compressed carbon dioxide energy storage system. This work provides a reference for selecting coupled solar energy schemes in next-generation long-duration energy storage systems.