# Financial Optimization of a Solar-Driven Organic Rankine Cycle
## 3 Results and Discussion
### Optimization Results  
The optimization of the examined system is performed in various ways. In the first part, there are single-objective optimization procedures and in the second part, there is a multi-objective optimization procedure. Tables 4-6 show the optimization results with different criteria and more specifically for maximizing the energy efficiency, minimizing the payback period and maximizing the net present value respectively. It is critical to state that the minimization of the payback period leads to the minimization of the LCOE in all the examined cases and thus there is not a separate table for LCOE minimization. Moreover, Tables 4-6 include results about the optimum collecting areas, according to different criteria, for all the examined storage tank volumes. Moreover, the overall optimum values can be found in these tables by observing all the results together. Figure 7: Simple payback period (**a**) for different collecting areas with the storage tank volume as the main parameter (**b**) for different storage tank volumes with the collecting area as the main parameter. Table 4 shows that the overall maximum yearly energy efficiency is 15.38% and it is found for a 140-m\({}^{2}\) collecting area and a 12-m\({}^{3}\) storage tank volume. In this case, the yearly electricity production is 38917 kWh, the payback period is 8.58 years, the yearly solar collector efficiency 52.22%, the LCOE is 0.0989 \(\epsilon\) kWh\({}^{-1}\) and the NPV is 102.63 k\(\epsilon\). Moreover, Table 5 proves that the overall minimum payback period is 8.37 years and it is found for a 160-m\({}^{2}\) collecting area and a 14-m\({}^{3}\) storage tank volume. In this case, the yearly electricity production is 43328 kWh, the yearly energy efficiency is 14.99%, the yearly solar collector efficiency 50.68%, the LCOE is 0.0969 \(\epsilon\) kWh\({}^{-1}\) and the NPV is 116.29 k\(\epsilon\). Furthermore, Table 6 shows that the overall maximum net present value is 123.21 k\(\epsilon\) and it is found for a 220-m\({}^{2}\) storage tank volume. \begin{table}
\begin{tabular}{c c c c c c c} \hline \(V\) & \(A_{capt}\) & \(E_{el  
collecting area and a 14-m\({}^{3}\) storage tank volume. In this case, the yearly electricity production is 48275 kWh, the yearly energy efficiency is 12.14%, the yearly solar collector efficiency 40.77%, the LCOE is 0.1025 \(\upepsilon\) kWh\({}^{-1}\) and the payback period 8.96 years. So, it can be said that different optimization criteria lead to different optimum design parameters. Thus, an extra multi-objective optimization procedure is conducted. Figure 8 is a depiction of the multi-objective optimization procedure. The energy efficiency and the NPV are used as the two goals that have to be maximized. This procedure has an energetic and a financial index and thus it is interesting. Moreover, the optimum design points with these two criteria separately give different results and so the multi-objective optimization is emerging. It was found that the optimum design is the one with a 160-m\({}^{2}\) collecting area and a 14-m\({}^{3}\) storage tank. This design is the one that has been found to be the best one for minimizing both the payback period and the LCOE. Thus, it can be said that this design can be adopted as the overall optimum case for the present system. At this point, it is interesting to state that the found values of the LCOE are around 0.1 \(\upepsilon\)/kWh. In the literature, the reported values are generally higher and thus this work shows that the optimization is able to significantly reduce the LCOE. More specifically, [PERSON] et al. [11] found the LCOE to range from 0.145 up to 0.280 \(\upepsilon\) kWh\({}^{-1}\), [PERSON] and [PERSON] [13] found the LCOE around 0.4 \(\upepsilon\) kWh\({}^{-1}\) and [PERSON] et al. [16] calculated the LCOE at 0.17 \(\upepsilon\) kWh\({}^{-1}\). So, this work has to add to the literature promising results about the financial viability of the solar-driven ORC technology.