Thermo-economic performance of a compressed CO2 energy storage system with a flexible gas holder

In recent years, engineers' eyes have been increasingly captured by the compressed CO2 energy storage since it is a competitive electricity storage technology equipped with massive renewable power plants. Nevertheless, how to design an effective system configuration, for instance the scenarios of storing CO2 in high and low pressures, vacillates to the left and right in the researchers. A CO2 energy storage cycle, configured by three section compression/expansion, two-tank heat storage, artificial tank for storing high pressure CO2 liquid and gas holder for storing ambient pressure CO2, is comprehensively examined in this paper. Both the thermodynamic and economic performances are considered. Results demonstrate that the round trip efficiency is capable of arriving at 71 % along with the levelized cost of electricity being 0.1252 $/kWh. Inspiringly, the system is operated with low pressures, charge pressure being 8 MPa and discharge pressure being 6 MPa. The turbomachineries are provided with the 68.18 % share of overall exergy destruction. The high pressure heater carries the largest exergy destruction among heat exchangers. By integrating with low grade waste heat of 39 degrees C, the efficiency can be further improved to 72.66 % with the levelized cost of electricity being 0.1242 $/kWh. Meanwhile, the discharge pressure should be raised to 6.58 MPa.