Thermodynamic analysis of novel carbon dioxide pumped-thermal energy storage system

To address the issue of instability in power systems caused by the large-scale integration of renewable energy into the grid, the importance of large-capacity energy storage technologies has been increasingly recognized. To cope with the large storage tanks required for compressed carbon dioxide energy storage systems, two carbon dioxide pumped-thermal energy storage systems are proposed and modeled. Thermodynamic analyses of systems are conducted and sensitivity analyses of key parameters are performed. Parameter improvements are conducted based on the results of sensitivity analyses. The results show that the Rankine cycle-based carbon dioxide pumped-thermal energy storage system achieves a higher round-trip efficiency. For the Rankine cycle-based carbon dioxide pumped-thermal energy storage system, most exergy destruction occurs within the heat exchange units, with the highest exergy destruction in the first regenerator, accounting for 18.16% of the total. Through parameter improvement, the round-trip efficiency of the Brayton cycle-based carbon dioxide pumped-thermal energy storage system can be improved from 49.83% to 62.83%, while the round-trip efficiency of the Rankine cycle-based carbon dioxide pumped-thermal energy storage system can be improved from 60.16% to 69.28%.