## 3 Results and Discussion  
The electrical and thermal performances of the four PV panels were experimentally evaluated during the days of 12, 13, 15, 16, and 17 October 2022 at the Mechanical Engineering Department, Kind Saud University, Riyadh, KSA. The ambient temperature and total irradiance at the same inclination angle of the PV panels are depicted in Figure 5, for the five investigated days from 9:30 to 16:30. The average ambient temperatures of Day 1 to Day 5 were 33.36 \({}^{\circ}\)C, 32.69 \({}^{\circ}\)C, 31.87 \({}^{\circ}\)C, 33.54 \({}^{\circ}\)C, and 31.77 \({}^{\circ}\)C, respectively, while the average irradiances were 739.53 W/m\({}^{2}\), 754.77 W/m\({}^{2}\), 730.68 W/m\({}^{2}\), 760.58 W/m\({}^{2}\), and 774.37 W/m\({}^{2}\) for the five days, respectively. The recorded average ambient temperature in October was moderate compared to the average maximum temperature of 43 \({}^{\circ}\)C in August, while the solar irradiance in October was the highest over the year in Riyadh. This condition helped in examining the effect of the melting temperature of the PCM that was selected for the summer season on the PV performance in other seasons. In addition, the reference PV (PV1) panel was not surrounded by a higher ambient temperature which allowed natural cooling to play a role in managing the PV1 panel's temperature. Although the speed and direction of the surrounding air might affect the results, the simultaneous comparison of the four PV panels at the same location made the comparison independent of the air movement. The mass flow rates of the circulated cooling water at the back of the PV/T-PCM (PV3) and the LCPV/T-PCM (PV4) were identical on the same day. They were 0.3703, 0.96246, 1.93014, 1.93014, and 3.9049 1/min for the five days starting from Day 1 to Day 5, respectively. The same flow rate was repeated for Day 3 and Day 4 because this value is very close to the typical one used for solar collectors. The effect of cooling water was minimal on the temperatures of the PV3 and PV4 panels during Day 1 compared to the other days, while increasing the cooling-water flow rate decreased the average temperature of the PV3 and PV4 panels, which was affected by switching from a laminar flow scheme to a turbulent flow scheme after Day 2, according to the given water mass flow rate. The differences in the three temperatures measured for each PV panel were minimal for the reference PV (PV1) panel, while there was a noticeable difference in the remaining panels that employed the PCM, between the top and bottom ones. This was attributed to the variation in the time required to start the melting of the PCM between the top and bottom of the PCM-based panels, particularly in the PV2 panel. The PCM played its role in controlling the panel temperatures to be mostly less than 47 \({}^{\circ}\)C for the PV3 and PV4 panels with the help of active cooling. However, using only the PCM effectively reduced the PV2 panel's temperature compared to the PV1 panel's temperature until noon at around 13:30 for the five days. After that, with the reduction in solar irradiance, the heat stored in the PCM along with its low thermal conductivity hampered natural cooling from taking place, which was different to what was noticed with the PV1 panel's temperature after noontime. This observation highlights the importance of coupling PV-PCM systems with active cooling or a mechanism for effective heat releasing. It is important to mention that the average inlet cooling-water temperature was 21.87 \({}^{\circ}\)C coming from a tank under the basement over the five days, and the minimum and maximum temperatures were 18.91 \({}^{\circ}\)C and 24.55 \({}^{\circ}\)C, respectively. This low temperature noticeably reduced the PV3 and PV4 panels' temperatures with the higher flow rate used on Day 5.