## 3 Results and Discussions
### Outdoor Performance  
The outdoor analysis lasted over 3 days, to monitor the performance of the proposed system during the day-night cycle. The setup is shown in Figure 10.  
The reference case and the enhanced panel were investigated in parallel under the same atmospheric conditions. In Figure 11, the front temperature of the simple PV panel (red line) and the enhanced panel (blue line) are depicted. Results showed that the enhanced panel had a minor temperature in the morning, while during the remaining hours it was warmer than the simple panel. Numerically, the deviation of the two temperatures is represented in Figure 12. Positive numbers indicate that the enhanced panel was colder, vice versa for the negative ones. The maximum difference measured was almost 6 \({}^{\circ}\)C. Considering a temperature coefficient of 0.5%/\({}^{\circ}\)C for a monocrystalline panel, this means an increase in the electric conversion of 3%. During the evening and at night, the PCM maintained the panel warmer, but without affecting the electric yield as there was no solar radiation. Figure 11: Front temperature of the simple PV panel (red line) and the enhanced panel (blue line). Figure 10: Experimental outdoor setup. The different performances resulting during the daytime hours, made a greater deepening necessary. An analysis was differentiated in the function of the state of the PCM, to find a correlation. Figures 13-15 show the temperature difference in the two systems with solid state PCM, during phase change and liquid phase, respectively. The red line indicates the front temperature of the simple panel, while the blue one the enhanced panel. The black line is the average of the two thermocouples dipped into the PCM, to measure the thermal level of the PCM. Figure 12: Deviation between the reference case and the enhanced panel. Figure 13: Temperatures during solid state PCM. The red line indicates the front temperature of the simple panel, the blue one the enhanced panel. The black line is the average of the two thermocouples dipped into the PCM. Figure 13 shows the difference of temperature between the two system while the PCM was still solid. As the PCM temperature increased, the two front temperatures started to differ slightly. In this period, the average temperature of the panel was 32.1 \({}^{\circ}\)C, while in the case of the enhanced one, it was 30.9 \({}^{\circ}\)C. This meant that in the solid state, an increase in the electric yield of around 0.5% was obtained. In Figure 14, the same trends are depicted during the solid-liquid phase change. The temperature of the PCM was nearly constant, and the different between the two panels was more pronounced. The melting process lasted about 2 h, and the enhanced panel was about 5 \({}^{\circ}\)C colder (53 \({}^{\circ}\)C against 48.2 \({}^{\circ}\)C of the simple panel) with an increase in the yield of 2.5%. Once the PCM was completely melted, the trend was reversed and the panel became increasingly warm, surpassing the reference one (Figure 15). In this phase, the enhanced panel turned out to be 2.8 \({}^{\circ}\)C warmer with a decrease in the yield of 1.4%. Globally, throughout the day, the enhanced panel was 0.5 \({}^{\circ}\)C warmer than the reference case. This was due to the negative contribution of the liquid phase, the only one with a negative deviation. The melting process, on the contrary, showed the best results. This meant that, once the melting process was completed, an extraction system shall be activated to return the PCM to the beginning of the melting zone and re-exploit the phase change. Accordingly, the difference in temperature between the two system was maximized. Results are reported in Table 3.  
Figure 14: Temperatures during the melting process. The red line indicates the front temperature of the simple panel, the blue one the enhanced panel. The black line is the average of the two thermocouples dipped into the PCM. Figure 15: Temperatures during liquid state PCM.