# Investigation of a Solar-Driven Organic Rankine Cycle with Reheating
## 3 Results and Discussion
### Yearly Energetic Performance  
The annual investigation of the studied configurations is very important in order to define their real performance. The climate conditions in Athens are selected for this analysis. One typical data for every month was examined, which is a usual methodology for solar thermal application analysis. Figure 10 displays the results of the yearly system efficiency of the reheat system for different electricity capacities and saturation temperatures. It is useful to state that a higher capacity leads to a higher yield, a reasonable result because greater nominal capacity offers the possibility to produce higher amounts of electrical energy, especially in summer when there is adequate solar potential. The global maximum system efficiency was found for 25 kW electricity capacity and 140 \({}^{\circ}\)C saturation temperature. In this design, system efficiency was 7.33%, ORC efficiency 18.09%, and collector efficiency is 40.70%. It is also useful to state that for this case, electricity production yield was maximized at 40.6 MWh. Figure 11 displays the monthly variation of the electricity yield production and system efficiency. It can be said that system efficiency is maximized in August, while yield production is maximized in July. Generally, the system has a higher performance in the summer compared to winter, an acceptable result because in the summer there is higher solar potential and the solar rays are more \"vertical\" in the ETC aperture.  
Figure 8: Daily system efficiency for different combinations of saturation temperature levels and electricity capacities (reheat case).  
Figure 10: Yearly system efficiency for the reheat ORC case for different combinations of saturation temperature levels and electricity capacities.  
Figure 9: Daily system efficiency enhancement with the reheat system compared to the simple system for different combinations of saturation temperature levels and electricity capacities.  
Figure 12 displays the yearly performance of the simple system, while Figure 13 shows the monthly performance for the optimum case. The maximum saturation temperature is selected to be up to 130 \({}^{\circ}\)C in order to avoid very high expansion ratios in the system. In addition, Figure 12 indicates that in high saturation temperatures, the system efficiency is significantly reduced, so this range is not interesting. According to Figure 12, the optimum saturation temperature of the ORC is found at 90 \({}^{\circ}\)C, while the capacity of 25 kW is the best choice. For this scenario, the yearly system efficiency is 5.45%, cycle efficiency is 10.81%, and collector efficiency is 50.51%. The electricity yield for this case is found at 30.2 MWh. Figure 13 shows that monthly efficiency is maximized in April and monthly yield in July.  
The energetic comparison of the two optimum scenarios indicates that the reheating system leads to 34.5% higher performance, which is an important enhancement. This result clearly shows that on a yearly basis, the suggested reheating configuration can lead to a significant enhancement in solar irradiation harvesting, which can make solar-fed ORC a viable choice for achieving the sustainable development goals of 2030 [30].