## 5 Results and Analysis
### Parametric Study Based on Thermodynamics and Exergoeconomics  
The system is equipped with some devices, such as the liquid storage tank, the compressor, and the turbine. And the liquid CO\({}_{2}\) pressure (\(P_{\rm liq}\)), compressor and turbine isentropic efficiencies (\(\eta_{\rm C}\), \(\eta_{\rm T}\)), and CO\({}_{2}\) evaporation pressure (\(P_{\rm evap}\)) are selected as main \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Component** & \(\dot{E}_{\rm F}\) & \(\dot{E}_{\rm P}\) & \(\dot{E}_{\rm D}\) & \(\epsilon_{\rm D}\) & \(\epsilon_{\rm F,k}\) & \(\epsilon_{\rm P,k}\) & \(\dot{C}_{\rm D,k}\) & \(\dot{Z}_{\rm k}\)+\(\dot{C}_{\rm D,k}\) & \(\gamma_{\rm k}\) \\  & **MW** & **MW** & **MW** & **\%** & **\%**/GJ** & **\%**/GJ** & **\%**/h** & **\%** & **\%** \\ \hline C & 14.08 & 12.92 & 1.15 & 28.43 & 13.89 & 24.82 & 57.61 & 508.76 & 88.68 & 78.73 \\ TES1 & 4.27 & 4.24 & 0.03 & 0.87 & 28.65 & 29.27 & 3.63 & 9.49 & 61.73 & 2.17 \\ TES2 & 2.21 & 2.02 & 0.19 & 4.67 & 28.65 & 31.67 & 19.53 & 21.94 & 10.98 & 10.54 \\ Cond & 6.45 & 6.36 & 0.09 & 2.24 & 28.65 & 29.11 & 9.36 & 10.67 & 12.26 & 1.63 \\ Valve & 6.36 & 6.27 & 0.09 & 2.17 & 29.51 & 29.94 & 9.34 & 9.62 & 3.00 & 1.44 \\ Evap & 6.27 & 6.19 & 0.08 & 1.99 & 29.94 & 30.48 & 8.70 & 11.95 & 27.24 & 1.79 \\ TES3 & 2.02 & 1.61 & 0.40 & 9.97 & 32.61 & 41.45 & 47.46 & 51.41 & 7.67 & 27.09 \\ TES4 & 4.23 & 4.06 & 0.17 & 4.27 & 29.83 & 31.24 & 18.59 & 20.61 & 9.77 & 4.73 \\ T & 11.38 & 10.00 & 1.38 & 34.19 & 32.23 & 38.43 & 160.76 & 223.03 & 27.92 & 19.22 \\ Cooler & 0.48 & 0.02 & 0.45 & 11.19 & 2.39 & 30.75 & 0.78 & 1.43 & 45.21 & 1185.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: System components’ exergy results. Figure 5: Operation cost ratio of system components. \begin{table}
\begin{tabular}{c c} \hline \hline
**Main Performances** & **Value** \\ \hline CO\({}_{2}\) mass flow rate/kg\(\cdot\)s\({}^{-1}\) & 29.75 \\ Compressor input power/MW & 14.08 \\ Turbine output power/MW & 10.00 \\ Energy storage efficiency/\% & 71.04 \\ System total exergy destruction/MW & 4.05 \\ Exergy efficiency/\% & 71.21 \\ Volume of GST/m\({}^{3}\) & 478.938.18 \\ Volume of LST/m\({}^{3}\) & 1342.50 \\ Volume of HST/m\({}^{3}\) & 367.22 \\ Volume of CST/m\({}^{3}\) & 339.16 \\ Volume of HWT/m\({}^{3}\) & 296.53 \\ Volume of CWT/m\({}^{3}\) & 239.41 \\ Cost per unit power product/USD-GJ\({}^{-1}\) & 40.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Main system performances under typical conditions. system variables, and their influences on the system energy storage efficiency (\(\eta_{\rm stor}\)) and the unit power product cost (\(c_{\rm P,tot}\)) are calculated and analyzed. Table 9 shows the ranges of key variables [54; 58]. Figures 6 and 7 show 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 \(P_{\rm liq}\), respectively. It is clear that \(M_{\rm CO_{2}}\) and \(\dot{W}_{\rm C}\) both decrease linearly with the increase in \(P_{\rm liq}\), while \(\eta_{\rm stor}\) and \(c_{\rm P,tot}\) both have opposite change with the increase in \(P_{\rm liq}\). The compressor input power per unit working medium rises with the increase in \(P_{\rm liq}\), while the turbine output power per unit working medium also rises for higher inlet temperature, which is improved by the greater compression heat. Because the increase in unit turbine power is slightly higher than unit compressor power, \(\eta_{\rm stor}\) is improved under the combined influences. Also, \(M_{\rm CO_{2}}\) decreases while the system total output power remains at 10 MW, leading to the decline in \(\dot{W}_{\rm C}\) with the rise in \(P_{\rm liq}\). Meanwhile, the rise in \(P_{\rm liq}\) could also induce higher wall thickness and investment cost of high-pressure components; hence, \(c_{\rm P,tot}\) is increased to some extent.