A trans-critical carbon dioxide energy storage system with heat pump to recover stored heat of compression

In this paper, the heat pump system is used as the thermal storage system to reheat the heat of compression of the trans-critical CO2 energy storage system based on the underground gas storage reservoir, and the thermodynamic analysis and sensitivity analysis of the main equipment of the energy storage system are carried out. Considering the limitation of the thermal properties of the heat storage medium, the influence of the energy storage system composed of different heat storage medium on the system performance is studied. Results have shown that the round-trip efficiency, energy storage efficiency and heat storage efficiency of the system are 66%, 58.41%, and 46.11%, respectively. With the increase of energy storage pressure, the round-trip efficiency and energy storage efficiency increase gradually, while the heat storage efficiency decreases first and then increases. When the energy storage pressure is 23 MPa, the system has the lowest heat storage efficiency. The round-trip efficiency, energy storage efficiency and heat storage efficiency increase with the increase of the energy recovery pressure. The study also shows that the energy storage system with water as the heat storage medium has the highest efficiency and the best performance.