# Financial Optimization of a Solar-Driven Organic Rankine Cycle
## 3 Results and Discussion
### Parametric Analysis
#### 3.1.1 Energy Analysis  
The first examined index is electricity production, which is the most important parameter. Figure 2a shows that higher collecting increases electricity production on a yearly basis. However, after the 160 m\({}^{2}\), the increasing trend of the curves reduces. Moreover, the curves for storage tanks between 16 and 30 m\({}^{3}\) are extremely close to each other, while for smaller tanks the electricity production is generally lower. Another interesting result is that for small collecting areas, the optimum storage tanks are smaller. More specifically, Figure 2b indicates that for collecting areas of 100 and 120 m\({}^{2}\), the optimum storage tank is the smallest examined (10 m\({}^{3}\)), while for higher collecting areas, the optimum volume increases. The results indicate that the optimum storage tank volumes generally range from 12 up to 16 m\({}^{3}\) in order to have the maximum electricity production. The yearly production of electricity can reach up to 52.16 MWh for a 300-m\({}^{2}\) collecting area and a 30-m\({}^{3}\) storage tank volume, which indicates a system that operates about 60% of the year.  
Figure 2: Electrical production (**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.  
It is useful to note that a higher storage tank gives the possibility for greater storage capacity and so higher solar irradiation amounts to be used in the afternoon after the sunset. Especially in the summer, the higher storage tank volumes are critical in order not to reach the maximum temperature limit of 400 \({}^{\circ}\)C and so not to stop the system operation for some hours per day. On the other hand, an extremely great storage tank leads to high thermal losses due to the high outer tank surface. Moreover, a very huge tank creates difficulties in the operation during the winter because there is not the ability to reach the temperature limit of 334.7 \({}^{\circ}\)C for operation.  
The next examined parameter is the yearly system efficiency. This fact shows the ratio of the produced electricity to the available solar irradiation of the examined days. Figure 3a illustrates that for every storage tank volume curve, there is a specific collecting area that maximizes energy efficiency. Generally, the maximum energy efficiency is found for collecting areas in the range from 120 to 140 m\({}^{2}\). The maximum yearly system efficiency is 15.38% and it is found for a 140-m\({}^{2}\) collecting area and a 12-m\({}^{3}\) storage tank volume.  
Figure 3: System efficiency (**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.  
Figure 3b shows that there is an optimum collecting area that maximizes the energy efficiency for all the storage tanks volumes from 14 up to 30 m\({}^{3}\). However, for the storage tanks of 100 and 120 m\({}^{2}\), the tank volume is the minimum examined of 10 m\({}^{3}\). At this point, it is critical to state that, in this work, the optimum collecting area for the smallest examined volumes is lower than 100 m\({}^{2}\) and thus some curves have different shapes in the examined range. However, this fact does not play any role in the overall optimum choice because the optimum designs are included in the examined ranges of collecting areas and storage tank volumes.