## 5 Results and Analysis
### Parametric Study Based on Thermodynamics and Exergoeconomics
The turbine power generation capacity falls with the decline in its inlet pressure, and rises with the increase in the turbine import temperature when other conditions remain unchanged. Therefore, the turbine unit power rises first and then drops with the effects of two factors, which leads to the above changing trend of \(\eta_{\rm stor}\). Meanwhile, the increase in \(P_{\rm evap}\) not only changes \(M_{\rm CO_{2}}\), which has a significant impact on the investment cost, but also increases the requirement of the wall thickness, pressure resistance, and sealing properties of high-pressure components. Therefore, \(c_{\rm P,tot}\) shows the U curve trace with the increase in \(P_{\rm evap}\). The following analyses examine the influences of key parameters on the system exergy efficiency (\(\eta_{\rm ex}\)) and the exergy destruction of each component. Figure 12 exhibits the changes of \(\eta_{\rm ex}\) and the exergy loss for system components with valid \(P_{\rm liq}\), and \(\eta_{\rm ex}\) increases with the increase in \(P_{\rm liq}\). The specific analyses of each component are as follows. For the compressor, the unit exergy loss per CO\({}_{2}\) rises because of the increase in the pressure ratio, but the total exergy destruction of the compressor drops with the decrease in \(M_{\rm CO_{2}}\); for the TES1, \(\Delta T\) rises with the increase in hot terminal temperature, causing the growth of its exergy loss; for the TES2, the specific heat capacity of CO\({}_{2}\) from the inlet section is more sensitive to the pressure, and it increases when \(P_{\rm liq}\) rises. Therefore, \(\Delta T\) in the inlet section comes down correspondingly, causing a decrease in the exergy loss; for the condenser, the exergy loss increases with the decrease in the heat transfer efficiency; for the throttle valve, the pressure drop increases and the exergy loss increases; for the evaporator, due to the increase in CO\({}_{2}\) inlet enthalpy, the heat transfer rate and the mass flow rate of the hot working medium both decrease, resulting in the decrease in the exergy loss; for the TES3 and TES4, they have the same tendency as the TES2 and TES1, respectively; for the turbine, due to the increase in the import temperature, the power generation capacity increases and the exergy loss decreases under the same inlet and outlet pressure; for the cooler, the exergy loss increases with the increase in \(\Delta T\). Figure 11: Influence of \(P_{\rm evap}\) on the system energy storage efficiency and unit power product cost. Figure 13 exhibits the changes of \(\eta_{\rm{ex}}\), \(\dot{E}_{\rm{D}}\), and exergy destructions of related components with valid \(\eta_{\rm{C}}\). \(\eta_{\rm{ex}}\) rises with the increase in \(\eta_{\rm{C}}\). It is because \(\dot{W}_{\rm{C}}\) and \(\dot{E}_{\rm{D}}\) both decrease with the increase in \(\eta_{\rm{C}}\); thus, \(\eta_{\rm{ex}}\) increases under the comprehensive effects. The specific analyses of the relevant components are as follows. For the compressor, the exergy loss decreases due to the increase in the power generation capacity; for the TES1 and TES4, the heat transfer rate decreases owing to the decrease in the outlet temperature during CO\({}_{2}\) compression, and thus, the exergy loss decreases; for the turbine, due to the drop in the inlet temperature, its unit power generation capacity decreases and the exergy loss increases; for the cooler, the exergy loss decreases due to the drop in the inlet temperature; for other components, the exergy loss increases with the increase in \(M_{\rm{CO}_{2}}\). Figure 14 presents the changes of \(\eta_{\rm{ex}}\) and \(\dot{E}_{\rm{D}}\) with valid \(\eta_{\rm{T}}\). \(\eta_{\rm{ex}}\) increases with the increase in \(\eta_{\rm{T}}\), while the system total exergy loss slumps with the decrease in \(M_{\rm{CO}_{2}}\). Figure 15 shows the changes of \(\eta_{\rm{ex}}\), \(\dot{E}_{\rm{D}}\), and exergy destructions of related components with valid \(P_{\rm{evap}}\). \(\eta_{\rm{ex}}\) climbs first and then drops with the increase in \(P_{\rm{evap}}\).