Accurate Modeling of Partially Shaded PV Arrays

Partial shading is the condition of nearby objects casting shade onto part of a photovoltaic (PV) array, causing the PV modules to receive non-uniform irradiance. Non-uniform shading causes electrical mismatch between elements within the array, resulting in a non-linear reduction in energy capture. Accurately modeling mismatch conditions is a particularly difficult problem due to the large number of parameters needed to fully define a PV system and its operating state. Furthermore, the large number of possible system state conditions make the models computationally complex. Previous work on this topic has addressed these difficulties by simplifying the system representation, reducing the number of parameters used, and limiting the domain space to simple irradiance patterns that may not be representative of real shade conditions. In this paper, we review common modeling approaches to address this problem and provide an overview of PV equivalent circuit theory. We then present PV Mismatch-free open-source software written in Python by the authors for simulating full PV system current-voltage curves. Finally, we demonstrate an improvement over common practice for modeling this type of behavior, illustrating that modeling mismatch behavior at the PV cell rather than PV module level provides more accurate results-up to 30% less over-prediction with respect to module level estimates-and better insight into system behavior.