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Second Quadrant Electrothermal Characterization of Photovoltaic Cells for Safe Reverse Bias Operation and Improved Shadow Performances

The operating point of photovoltaic (PV) cells on the panel can shift from the first to the second quadrant (IIQ) of their current-voltage (IV) plan under certain conditions such as shading. This causes power losses, heat sinking, and hot spots (HS) mainly on the shadowed cell. Manufacturers match cells according to their IV measurement in the first quadrant (IQ) and add a bypass diode (DBS) to alleviate the related issues. However, these solutions cannot avoid the IIQ operation of the involved cell which results in HS. This paper presents the importance of IV electrothermal characterization of solar cells IIQ to mitigate HS. Additionally, it investigates the IIQ safe operation of different types of cells. Accordingly, we examine the power balance of a partially shaded PV panel in different operating points with individual IIQ of IV cell profiles. This work utilizes an experimental bench which has been developed to characterize the reverse behavior. An infrared thermal camera with ResearchIR software is used to evaluate temperature distributions of the cells surface and HS. Moreover, an environmental chamber is used to observe heating effects on the IV curves and breakdown (BD) mechanisms. The results demonstrate that the IV IIQ characteristics are inherently tied to the cell's thermal properties. In addition, the power losses of each type of cells with HS damage is simulated to define worst-case scenarios. As a result, the ability of high BD to survive IIQ operation excels cell with low or secondary BD. Indeed, this paper elaborates remarks to enhance shaded PV panel performance and safety regarding real implementations.