# Numerical and Parametric Analysis for Enhancing Performances of Water Photovoltaic/Thermal System
## 3 Results and Discussion
### Parametric Analysis
#### 3.2.2 Effect of Water Film Thickness  
Among the other geometry parameters for flow, the water film thickness presented an important effect on the optimized cooling of the PV cells and the PV/T electrical and thermal performances. Hence, four water thicknesses of 3 mm, 5 mm, 7 mm, and 10 mm were selected to investigate its impact on the cooling of the PV cells with water velocity and inlet temperature ranging from 0.010 to 0.035 m/s and 20 to 30 \({}^{\circ}\)C, respectively. The study was carried out under the same weather conditions mentioned above (solar irradiance of 1000 W/m\({}^{2}\), outdoor temperature of 35 \({}^{\circ}\)C, and wind speed of 1 m/s). Figure 4: Effect of water velocity on the cooling of the PV cells for different thicknesses: (**a**) \(\delta\) = 3 mm, (**b**) \(\delta\) = 5 mm, (**c**) \(\delta\) = 7 mm, (**d**) \(\delta\) = 10 mm. As illustrated in Figure 5, as the water film thickness increased (3 mm, 5 mm, 7 mm) for the different water velocity cases, the PV temperature decreased. This is due to the important heat removed from the PV panel, while by further increasing the water film thickness from 10 mm the PV temperature start increasing (inflexion point). As a result, a minimum value of PV temperature was noted to be 27.7 \({}^{\circ}\)C for an optimal water film thickness of 7 mm (water inlet temperature and velocity of 20 \({}^{\circ}\)C and 0.035 m/s, respectively). In Figure 6, the effect of the water film thickness on the fluid heat transfer coefficient and thermal power is illustrated for variable water velocity and inlet temperature. From this figure, it can be seen that with the increase in water thickness, the heat exchange coefficient dropped which decreases the fluid outlet temperature. However, the thermal power is higher than the thermal power, which is due to the increase in water thickness. Figure 5: Effect of water thickness on the cooling of the PV cells for different velocities: (**a**) V = 0.01 m/s, (**b**) V = 0.015 m/s, (**c**) V = 0.02 m/s, (**d**) V = 0.025 m/s, (**e**) V = 0.035 m/s. According to Equation (27), the thermal power was not only depending on difference between the inlet and the outlet temperature, but also a function of the water mass flow rate. At a fixed value of water inlet temperature and velocity, the thermal power is related to the water mass flow rate and the outlet temperature. In this study, the water film thickness increase clearly affected the cooling of the PV unit and the heat gain. Noting that, further increase of water thickness will also affect the cost and the PV/T system heavy weight. Consequently, the PV/T system with a coupled optimum water velocity and thickness of 0.035 m/s and 7 mm provided the best cooling effect and highest electrical and thermal performances (Table 4). The PV and PV/T performances were also depicted and compared under real weathers conditions of Iasi, Romania. A daily simulation was conducted for a typical day of summer (28 July 2016), with weather data involving solar irradiance \(E_{sun}\) and ambient temperature \(T_{a}\) reported by the PVGIS data [36] as shown in Figure 7. During this day, a maximum solar irradiance about 1022 W/m\({}^{2}\) and ambient temperature of 27.6 \({}^{\circ}\)C were noted at 13:00. The simulation was done supposing the inlet water temperature for PV cooling equal to the ambient one with a maximum temperature of 27.6 \({}^{\circ}\)C. The optimum case of PV/T system was chosen in terms of water velocity of 0.035 m/s and water film thickness of 7 mm. Given these weather conditions, the evolution of PV and PV/T temperatures (PV/T at \(T_{int}\) = \(T_{a}\)) is illustrated in Figure 8. It can be clearly observed that both temperatures presented the same trend during this day. Moreover, the PV/T system provided a lower PV cell temperature of 33.8 \({}^{\circ}\)C at 13:00, due to the cooling effect compared with the conventional PV unit (61 \({}^{\circ}\)C).