Proposal and thermo-economic analysis of a combined cooling, heating, and power system based on compressed CO2 energy storage with external heat source

With the rapid development of intermittent renewable energy, large-scale energy storage has become a critical technique to maintain the balance of the power grid. In this study, a novel combined cooling, heating, and power system based on compressed CO2 energy storage with external heat source was proposed. Thermodynamic and economic models of the system were developed, and performance evaluation indicators, including equivalent round-trip exergy efficiency (RTE), energy storage density (ESD), and levelized cost of energy (LCOE) were defined to analyze and evaluate system performances from energy, exergy, and economic perspectives. Additionally, influences of key parameters were analyzed. The results show that the system achieves the RTE of 69.97%, ESD of 0.1498 kWh∙m−3 and LCOE of 0.0935 $∙kWh−1 under the design condition while delivering auxiliary outputs of 7.68 MW high-temperature steam, 3.01 MW medium-temperature hot water, and 0.56 MW cooling power. Heat exchangers are the primary sources of exergy destructions accounted for 61.61% of total exergy losses and representing 30% of total equipment investment. According to parameter analysis, a liquid storage tank pressure of 10 MPa can maximize RTE and minimize LCOE. The increased external heat source temperature can improve thermodynamic and economic performances while the heat feedback rate has little impact on RTE, but it increases LCOE. The second-stage turbine outlet pressure significantly affects the cooling supply of the system but may pose a challenge to system safety. Multi-objective optimization is implemented to derive the optimal performance, achieving a RTE of 70.98% and a LCOE of 0.0737 $∙kWh−1.