Modeling Local Bias in Partially Shaded Solar Modules as a Basis for Assessing Stress on the Cells

Partial shade can cause electrical and thermal stress that accelerate degradation. A first step to quantifying that stress is to understand the local electrical bias of each component, also enabling modeling of the local heating. This work quantifies the local electrical bias as a function of operating conditions using measured data to derive the reverse-bias I-V characteristics of the solar cells from module-level I-V curves and then constructing module I-V curves for arbitrary shading conditions. For each module bias point, the local current and voltage are quantified for each solar cell, enabling estimation of each cell’s operating bias and temperature (and associated degradation). Forward bias operation does not result in significant heating but can cause degradation for cells sensitive to injected minority carriers. Our empirical algorithm can be applied to any module without prior knowledge of the cells’ characteristics.