# Electrical and Thermal Behaviour of Crystalline Photovoltaic Solar Modules in Shading Conditions
## 2 Materials and Methods  
To study the electrical and thermal behaviour of crystalline PV modules under shading or soiling, three tests were made. The first test was focused to measure the electrical current through bypass diodes of the whole I-V characteristic curve. The second and third test was focused on studying the electrical and thermal behaviour in different operational voltage points under different shading and the electrical current of the corresponding bypass diode. The first and second tests were carried out on a monocrystalline PV module LUXOR LX195M/125-72 +, and the third test was carried out on a polycrystalline PV module AXTEC AC-250 P/60S. Monocrystalline and polycrystalline PV modules are composed of 72 and 60 PV cells, respectively, which are grouped in 3 substrings, each protected by a bypass diode. The tests were carried out in the absence of cloudiness. In the first test, the monocrystalline PV module was connected to a group of variable resistors. By varying the value of the resistances it was possible to characterize the I-V curve for each of the shadow sequences proposed. The proposed shadows, which are detailed below, are based on covering a single cell of each substring chosen at random. The resistance of the group gradually decreased from values of open circuit to short circuit. As the value of the resistance varied, voltage and current data were recorded. Electrical current values were obtained for each of the bypass diodes, as well as the total of the PV module. For the measure of the 3 bypass diode currents, the output PV module current, and the output PV module voltage, 4 DC ammeters and a Fluke 177 voltmeter were connected. The irradiance values were measured with a power analyser HT-SOLAR 300N for PV applications. In the second and third test, the respective PV modules, separately, were exposed to external environmental conditions and connected to a programmable electronic load, which allowed us to set an output voltage for all possible values of the I-V curve. The effect of the partial shading was done by covering different PV cells through an adhesive tape with a known emissivity value. The front temperature of the PV module was measured by infrared thermography. The voltage value of the programmable electronic load was modified depending on the experimental behaviour of bypass diodes. A total of 3 cells belonging to the 3 different substrings were covered to evaluate the performance of the 3 bypass diodes. The PV cells were covered one by one progressively every 30 min to reach a thermal stabilization. Then, the covered PV cells were uncovered until the PV module came back to the initial operating condition. PV cells were covered randomly without considering those close to the frame, to avoid its thermal effect. The sequence of covering and uncovering PV cells were carried out according to the following sequence, whose identification of the covered PV cell was done as indicated in the specification IEC-62446-3 [21]. Step 1. Covering E3 cell of 1 st substring;  
Step 2. Covering C4 cell of 2 nd substring;  
Step 3. Covering B6 cell of 3 rd substring;  
Step 4. Uncovering C4 cell of 2 nd substring;  
Step 5. Uncovering E3 cell of 1 st substring;  
Step 6. Uncovering B6 cell of 3 rd substring. The electrical behaviour of the second and third tests was studied by measuring the current of each diode as indicated in Figure 1. A total of four HAMEG HM8012 digital DC ammeters were connected, measuring the current through each bypass diode, as well as the total output current of the PV solar module. The thermal behaviour of the PV module was studied by measuring the temperature. Contact sensors and an IR thermography camera measured the back and front side PV module temperature, respectively. The environmental parameters (horizontal irradiance, ambient temperature, and wind speed) were recorded by a weather station located on the site. The equipment was connected as shown in Figure 2.  
Figure 1: Electronic load and digital DC ammeters diagram connection in the photovoltaics (PV) module.