# Investigation of a Solar-Driven Organic Rankine Cycle with Reheating
## 4 Conclusions  
The goal of the present work is the analysis of a solar-fed organic Rankine cycle with reheating and its comparison with the conventional organic Rankine cycle. Both ORCs include a recuperator after the expander device, while the solar field consists of evacuated tube collectors. The comparative analysis is conducted mainly on dynamic conditions with a created model in Engineering Equation Solver. The analysis is energetic and economic for the weather data of Athens. Below, the most valuable conclusions are briefly presented:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Reheat ORC** & **Simple ORC** \\ \hline \(T_{sat,opt}\) (\({}^{\circ}\)C) & 130 & 90 \\ \(P_{d,mean,opt}\) (kW) & 15 & 10 \\ \(\eta_{sys,y}\) & 6.98\% & 5.09\% \\ \(\eta_{ORC,y}\) & 16.94\% & 10.46\% \\ \(T_{sol,y}\) & 41.44\% & 48.82\% \\ \(E_{d}\) (kWh) & 38,721 & 28,213 \\ _SPP_ (years) & 10.04 & 10.84 \\ _NPV_ (\(\xi\)) & 68,004 & 44,008 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of the optimum scenarios for maximization of the NPV.  
The reheating system presents higher performance mainly due to the lower expansion ratio in every expanding device and consequently to higher isentropic efficiency.  
For the reheat ORC, the global maximum system efficiency is found for 25 kW electricity capacity and 140 \({}^{\circ}\)C saturation temperature. The yearly system efficiency is 7.33%, ORC efficiency is 18.09%, and solar field efficiency is 40.70%.  
For the simple ORC, the global maximum system efficiency is found for 25 kW electricity capacity and 90 \({}^{\circ}\)C saturation temperature. The yearly system efficiency is 5.45%, ORC efficiency is 10.81%, and solar field efficiency is 50.51%.  
The optimum financial capacity is 15 kW for the reheat case and 10 kW for the simple case. The optimum saturation temperature is 130 \({}^{\circ}\)C for the reheat system and 90 \({}^{\circ}\)C for the simple case.  
It is important to state that the optimum financial designs are found for the smaller capacities, while these present lower efficiency than higher capacities. This result indicates that the increase in capacity does not lead to a significant energy yield increase in order to overcome the extra cost due to the extra capacity.  
It is useful to highlight that the results of this work indicate that the reheat system can operate in higher saturation temperatures compared to the simple system.  
For optimum cases according to the NPV maximization, system efficiency for the reheat system is 6.98%, presenting an increase of 37.1% compared to the conventional case.  
The maximum NPV for the reheat ORC is found at 68 k\(\xi\), while it is 44 k\(\xi\) for the simple ORC.  
In the future, this system can be investigated with different working fluids (e.g., mixtures), phase change materials in storage devices, and other heat sources. Biomass and concentrating solar collectors are interesting choices that can be checked with the ORC reheat cycle.  
Conceptualization, E.B.; methodology, E.B. and P.L.; software, E.B., P.L. and C.T.; investigation, E.B.; writing--original draft preparation, E.B., P.L. and C.T.; writing--review and editing, E.B., P.L. and C.T.; supervision, C.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data available after request.  
The authors declare no conflict of interest.