I. Introduction
Accurate performance prediction of PV systems with shading is important. PV systems are often built with shading either from adjacent rows or from obstacles both near and far. Variable terrain and uneven row spacing may compound row to-row shading. Shade can decrease PV system performance up to 20% by decreasing incident irradiance on cells in the module and changing their electrical response [1]. This causes electrical mismatch at both the module and string level because circuits in series must carry the same current, and circuits in parallel must have the same voltage. Unfortunately, electrical mismatch is not linear with shading, so using a constant shade impact factor (SIF) with a point performance model will be inaccurate [2]. Therefore, accurate performance prediction of a PV system with complex shading requires a continuous model of the current and voltage relation to account for non-linear electrical mismatch [3], [4].