# Electrical and Thermal Behaviour of Crystalline Photovoltaic Solar Modules in Shading Conditions
## 3 Results and Discussion
On top of Figure 8, the covered cell in each step has been represented, showing the results below each one. Depending on the covered PV cell and the voltage output of the PV module established, the bypass diode currents and total output current are shown. The test is carried out in the absence of cloudiness and with an irradiance interval between 798 W/m\({}^{2}\) and 970 W/m\({}^{2}\). Figure 9 shows the output voltage point set by the programmable electric DC load in each step of test 2. If any cell is covered and if the output voltage is close to the MPP of the module, the output current will be much lower than the MPP current, and no bypass diode will carry an electrical current. However, when the output voltage point set is changed to certain lower levels, the total output current increases, while the bypass diode starts to carry an electrical current. In this case, the number of bypass diodes turned on will depend on sub-modules with an affected PV cell. Something different happened when all sub-modules were affected by a covered PV cell since the total output current was lower than the MPP one and no bypass diode was turned on. As Figures 8 and 9 show, in step 1, a PV cell was covered, while the programmable DC electronic load was set at 35 V, giving place to a decrement of the current from 4 A to 0.7 A without turning any bypass diode on. Once the imposed voltage was changed to a lower value, 10.3 V, the behaviour of the  
Figure 8: Total output PV module and bypass diode currents measured in test 2. Figure 7: Experimental monocrystalline solar module I–V characteristic curve in condition 4.  
system changed completely, since the total output current increased up to 4.5 A and the bypass diodes of the sub-modules affected started to carry an electrical current of 3.9 A. The imposed voltage in step 3 was decreased up to 5 V without turning any bypass diode on, because all sub-modules had one PV cell covered. In steps 4, 5, and 6 the imposed voltage was kept constant at 5 V and the behaviour of the PV module was the same as shown in steps 3, 2, and 1, respectively. Figure 9 also shows the output power in each step according to the output voltage imposed by the programmable DC electronic load. As the PV module was working with a low voltage value, the output power kept a constant low value between 40 and 50 W  
Figures 12 and 13 show the thermal results obtained in test 2. Figure 12 shows the measurements obtained by an IR thermographic camera from the front side of the PV module, while Figure 13 shows the measurements obtained by the thermocouples connected on the back side of the PV module. The evolution of both temperatures through the six steps is similar in both measurements. However, it was noticed that the temperature on the back side is about 10 \({}^{\circ}\)C higher than the temperature on the front side. It was possible due to the thermal conductivity of the materials and the different ventilation produced by the wind on each side of the PV module. In steps 1 and 2, the temperature measured in the covered PV cells was higher than the healthy cell, F4, which was not covered. Those temperatures are limited by the bypass diode when turned on. However, the temperature in step 3 was lower than previous steps 1 and 2 and approached that of F4, since each sub-module shared a covered PV cell. Due to having one cell of each sub-module covered, the total output current is low at any voltage, so covered cells convert less energy into heat and become cooler than before. Figure 11: Programmable DC electronic load voltage imposed and output power in test 3. \[I_{di}=I_{p}-I_{p^{\prime}} \tag{1}\]0 Infrared (IR) thermographic camera temperatures on the front side of the PV module in test 2. Figure 14 shows PV module IR images on the first three steps in test 2. IR images show that PV cells kept higher temperatures when they were covered. Furthermore, an overheating of the junction box is noticeable when bypass diodes were turned on. Figures 15 and 16 show the thermal results obtained in test 3.