## 5 Results and Analysis
### Parametric Study Based on Thermodynamics and Exergoeconomics
Figures 8 and 9 exhibit the changes of the CO\({}_{2}\) mass flow rate (\(M_{\rm CO_{2}}\)), system total input (\(\dot{W}_{\rm C}\)), system energy storage efficiency (\(\eta_{\rm stor}\)), and unit power product cost (\(c_{\rm P,tot}\)) under valid \(\eta_{\rm C}\), respectively. \(\eta_{\rm C}\) is the main index to measure the compressor performance, and the increase in \(\eta_{\rm C}\) represents the decrease in the unit power consumption per CO\({}_{2}\) under the same condition. The increase in \(\eta_{\rm C}\) causes the decrease in the compressor export temperature as well, and the heat reserved in the hot salt tank and the hot water tank decrease correspondingly. Thus, the turbine inlet temperature drops, and the unit output  
Figure 6: Influence of \(P_{\rm liq}\) on the CO\({}_{2}\) mass flow rate and compressor input power. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variables** & **Unit** & **Range** \\ \hline Storage pressure & MPa & 6.5–7.1 \\ Evaporation pressure of CO\({}_{2}\) & MPa & 5.0–6.0 \\ Compressor isentropic efficiency & \% & 75.0–85.0 \\ Turbine isentropic efficiency & \% & 80.0–90.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Variation of key parameters. power generated during the energy release process also goes down. Thus, \(M_{\text{CO}_{2}}\) would rise with a constant \(\dot{W}_{\text{T}}\). With the increase in \(\eta_{\text{C}}\), the decrease extent of the compressor unit power is higher than the changes of the turbine unit power, resulting in the increase in \(\eta_{\text{stor}}\) and the decrease in \(\dot{W}_{\text{C}}\). Furthermore, the lower compressor export temperature brings down the heat transfer rate and the high-temperature resistance requirement of the TES1, TES4, and HST, inducing the decrease in the investments of the above components. Therefore, \(c_{\text{P,tot}}\) maintains a prominent upward tendency due to the co-influence. Figure 8: Influence of \(\eta_{\text{C}}\) on the CO\({}_{2}\) mass flow rate and compressor input power. Figure 7: Influence of \(P_{\text{liq}}\) on the system energy storage efficiency and unit power product cost. Figure 10 presents the changes of \(\eta_{\rm stor}\) and \(c_{\rm P,tot}\) with the changes of \(\eta_{\rm T}\). It could be seen that \(\eta_{\rm stor}\) increases with the increase in \(\eta_{\rm T}\), while \(c_{\rm P,tot}\) shows the U curve trace. The change of \(\eta_{\rm T}\) will not affect the energy storage process, and the compressor input power and the heat recovered in the system energy storage process remain unchanged. When \(\eta_{\rm T}\) increases, the unit mass CO\({}_{2}\) with unchanged import parameters generates more power during the expansion process, making \(\eta_{\rm stor}\) demonstrate a rising trend. For \(c_{\rm P,tot}\), the investment cost of the turbine rises with the increase in \(\eta_{\rm T}\), whereas the investment costs of other system components decrease with lower \(M_{\rm CO_{2}}\). Because the investment cost proportion of the turbine is large, \(c_{\rm P,tot}\) declines first and then increases with the increase in \(\eta_{\rm T}\). Figure 10: Influence of \(\eta_{\rm T}\) on the system energy storage efficiency and unit power product cost. Figure 9: Influence of \(\eta_{\rm C}\) on the system energy storage efficiency and unit power product cost. Figure 11 exhibits the changes of \(\eta_{\rm stor}\) and \(c_{\rm P,tot}\) with changed \(P_{\rm evap}\). \(\eta_{\rm stor}\) reveals a tendency of first rising and then decreasing with the increase in \(P_{\rm evap}\), and there is an optimal evaporation pressure point enabling the highest \(\eta_{\rm stor}\). \(c_{\rm P,tot}\) declines a little and then increases with the increase in \(P_{\rm evap}\), and the change extent is negligible. The reason is as follows. CO\({}_{2}\) with lower pressure could be heated to a higher temperature for unchanged compression heat. Thus, the increase in \(P_{\rm evap}\) induces the improvement of the turbine import pressure and the decrease in the turbine import temperature.