# Electrical and Thermal Behaviour of Crystalline Photovoltaic Solar Modules in Shading Conditions
## 4 Conclusions  
This article analyses the output current of the PV module, the bypass diode electrical behaviour, and the thermal response of a PV polycrystalline and monocrystalline module under conditions of shading or soiling. These conditions can occur in greenhouses with the possibility of dirt and shading of modules.  
Both electrical and thermal PV module behaviour in shading or soiling depends strongly on the operation voltage point imposed by the system, turning on the bypass diode or not. If the PV module is operating under voltage values below the knee of the I-V curve, which means that the output current is still high, the covered PV cell limits the current through the sub-module. Therefore, the remaining current that can produce the uncovered cells belonging to other sub-modules is derived by the bypass diode of the covered cell sub-module. In this case, the covered PV cell will increase its temperature with regards to uncovered ones. This electrical behaviour is maintained until at least one cell of every sub-module is covered. Then, the total output current decays at very low values, and the bypass diodes don't conduct any current or a very low value of it (mainly due to differences between the shading of different cells).  
When the bypass diode is turned on, the temperature of it increases as a result of the circulation of the current. The temperature of the covered cell increases quickly, while the temperature of the rest of the cell belonging to the sub-module affected increases more slowly. It was noticed that a relationship exists between the bypass diode temperature and the current that flows through it.  
Figure 16: Thermocouple temperatures on the back side of the PV module in test 3.  
Figure 15: IR thermographic camera temperatures on the front side of the PV module in test 3.  
**Author Contributions:** Conceptualization, G.A.-T., C.G.-L., J.A.C.-B., and A.G.-G.; methodology, [PERSON]-T. and C.G.-L.; validation, R.J.-C.; formal analysis, [PERSON]-[PERSON], [PERSON], [PERSON], and [PERSON]; investigation, [PERSON]-[PERSON], [PERSON], and [PERSON]; data curation, [PERSON], [PERSON], [PERSON], and [PERSON]; writing--original draft preparation, [PERSON], [PERSON], and [PERSON]; writing--review and editing, [PERSON]-[PERSON], [PERSON], [PERSON], and [PERSON]-[PERSON]; visualization, [PERSON]-C.; supervision, [PERSON]-C.; project administration, [PERSON], [PERSON], and [PERSON].  
**Funding:** This research received no external funding.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Abbreviations**  
**Acronyms:**  
PV Photovoltaic  
MPPT Maximum power point tracking  
IR Infrared  
MPP Maximum power point  
LMMP Local maximum power point  
GMPP Global maximum power point  
**Nomenclature:**  
\(I_{di}\) Bypass diode current \(i\) in the substring with the covered PV cell  
\(I_{p}\) Total PV module current when \(V_{p}<V_{\alpha}-V_{S}\)  
\(V_{p}\) Operating voltage of the solar PV module  
\(V_{\alpha c}\) Open circuit PV module voltage  
\(V_{S}\) Open circuit PV module voltage of the substring with the covered PV cell  
\(N_{S}\) Number of PV cells in a substring protected by a bypass diode  
\(V_{f}\) Crystalline silicon cell forward voltage  
\(I_{p^{\prime}}\) Total PV module current when \(V_{p}\geq V_{\alpha c}-V_{S}\)