## 4 Results and Discussion  
### Parameter Study  
It is very important to study the influence of key parameters on system performance. Thus, the parameter study, including effects of turbine inlet temperature and pressure, compressor inlet temperature, and pressure on specific work, overall efficiency, and cost of core equipment is performed. In order to make a fair comparison of the three types of cycles, and considering that the solar collector used is the parabolic trough solar collector, the basic condition is shown in Table 4.  
Figures 7-9 show the results of the parameter study on three cycle layouts. It should be noted that the heat exchange efficiency and working temperature of the parabolic trough solar collector are \begin{table}
\begin{tabular}{l l l} \hline \hline
**Constant Parameters in the Cycle** & **Value** & **Unit** \\ \hline Temperature of environment & 25 & \({}^{\circ}\)C \\ Isentropic efficiency of turbine & 85 & \% \\ Isentropic efficiency of compressor & 80 & \% \\ End temperature difference in regenerator & 10 & \({}^{\circ}\)C \\ Direct solar radiation intensity & 1000 & W/m\({}^{2}\) \\ Recuperator effectiveness & 95 & \% \\ Turbine inlet pressure & 18 & MPa \\ Turbine inlet temperature & 350 & \({}^{\circ}\)C \\ Compressor inlet pressure & 8.0 & MPa \\ Compressor inlet temperature & 35 & \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Base condition for the parameter study. Figure 6: Results of the present study compared to data from [PERSON]’s and [PERSON]’s studies. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Constant Parameters in the Cycle** & **Value** & **Unit** \\ \hline Re-heating pressure & 16.19 & MPa \\ Turbine efficiency & 93 & \% \\ Compressor efficiency & 89 & \% \\ Recuperator effectiveness & 95 & \% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._low, so overall efficiency of the three cycles are low, but the actual thermal cycle efficiency of them is about 25%-30%, while the turbine inlet temperature is 350 \({}^{\circ}\)C. In contrast, due to the limitation of the inlet temperature of the turbine, the actual thermal efficiency of ORC Rankine cycle is basically 20%-24% [41], which is lower than the actual thermal efficiency of the S-CO\({}_{2}\) cycles in this study. However, for the steam Rankine cycle, the overall efficiency is 24.5% when the turbine inlet temperature is 390 \({}^{\circ}\)C, which is higher than the S-CO\({}_{2}\) cycles in this study [42]. However, S-CO\({}_{2}\) cycles have fewer phase changes, so it needs no condenser arrangement and can reduce the number of valves, resulting in fewer total area and cost. Figure 7 illustrates the effects of the above parameters on a simple recuperated cycle, respectively. Specific work, overall efficiency, and cost of core equipment increase with the rising turbine inlet temperature and pressure, as shown in Figure 7a,b. Figure 7c shows that the specific work decreases and cost of core equipment increases with the rise of the compressor inlet temperature due to the increase of compression work. However, the overall efficiency changes tinily, and then decreases as the compressor inlet temperature rises. Figure 7d is the influence of compressor inlet pressure on specific work, overall efficiency, and cost of core equipment. In the range of compressor inlet pressure, there will be extreme values of specific work and overall efficiency due to pseudo critical pressure. Figure 8 illustrates the effects of the same parameters on the intercooling cycle respectively. Similar to the simple recuperated cycle, the relevant parameters generally increase as the turbine inlet temperature and pressure rises, which is shown in Figure 8a,b. It can be seen from Figure 8c that the cost of core equipment increases while specific work and overall efficiency decreases as the compressor inlet temperature rises. Figure 8d shows that overall efficiency and the specific work firstly increases as the compressor inlet pressure rises, and then decreases.