# Dynamic Investigation of a Solar-Driven Brayton Cycle with Supercritical CO2
## 4 Conclusions  
In this study, a dynamic investigation of a solar-driven power plant was conducted. This STP integrates a solar thermal system with a Brayton cycle through a counter-current heat exchanger. The solar thermal system is a solar tower, combined with a heliostat field and two TES. The Brayton cycle operates with sCO\({}_{2}\) as its working fluid. The modeling of the solar thermal system was created based on the mass and energy balance analysis. The modeling of the thermodynamic cycle was created based on the fundamentals of thermodynamics. The mathematical modeling for all the components that form the total system was developed using Modelica, a powerful programming language for modeling dynamic systems. The simulation process was done using the Dymola software, a software that integrates and simulates models based on Modelica. The main conclusions of this study are the following:  
* The optical efficiency was found to be 63.8%, whereas the thermal efficiency was found to be 50.7%. The thermodynamic efficiency of the cycle was calculated at 42.9%, and finally, the total system efficiency was 18.0%. * The total thermal losses of the central receiver are mainly the result of the thermal losses due to convection, but thermal losses due to radiation also exist. * The total system efficiency presents an increasing rate during the first hours of sunlight and the last hours before sunset. This efficiency increase is due to the usage of the two TES. * The net electrical power output presents a peak during the summer, where the density of DNI is higher and the TES is fully charged. * The use of a recuperator increases the system and the thermodynamic cycle efficiencies. Without the use of such a regenerator, the annual average system efficiency is found to be 16.1%, and the annual average thermodynamic cycle efficiency is found to be 34.2%. These values are significantly lower compared to the respective values of 18% for the system efficiency and 42.9% for the cycle efficiency with the recuperator. In the future, the present system will be optimized, and it will also be examined for different climate conditions. Moreover, different configurations of gas turbines can be examined, for example, with intercooling in the compression and multi-stage expansion with reheating. Furthermore, economic and environmental analysis can be performed. \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & & \multicolumn{4}{c}{**Efficiency Index [\%]**} \\ \hline
**Studies** & \(\mathbf{n_{o}}\) & \(\mathbf{\eta_{th}}\) & \(\mathbf{\eta_{cycle}}\) & \(\mathbf{\eta_{sys}}\) \\ \hline Current study & 63.8 & 50.7 & 42.9 & 18.0 \\ \hline [PERSON] et al. (2015) & 65.0 & - & 35.4 & - \\ \hline [PERSON] et al. (2019) & 64.1 & - & - & - \\ \hline [PERSON] et al. (2018) & 67.1 & - & - & - \\ \hline [PERSON] et al. (2014) & - & - & - & 16.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Annual average efficiency indexes for STP modeling. **Author Contributions:** Conceptualization, C.S., E.B., C.T. ; methodology, C.S., A.K., P.L., E.B. ; software, C.S., A.K., E.B. ; investigation, C.S., A.K., E.B. ; resources, C.S., P.L. ; data curation, C.S., A.K., P.L. ; writing--original draft preparation, C.S., A.K., P.L., E.B., C.T. ; writing--review and editing, C.S., A.K., P.L., E.B., C.T. ; supervision, E.B., C.T. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Available after request. **Conflicts of Interest:** The authors declare no conflict of interest.