Near-field partial shading on rear side of bifacial modules

It is well-known that near-field shading reduces the power output of a PV system drastically, especially when inhomogeneous shading creates a large current mismatch between series-connected solar cells. Typically, the front side irradiance is very uniform and near-field shading is avoided. In contrast, for bifacial panels, the rear side contribution is effected much more, both by the inhomogeneity of the rear irradiance and by (unavoidable) near-field objects, including the mounting system. In this paper, outdoor and indoor irradiance and IV measurements are combined with LT-spice modelling to show the limited effect of rear side shading on the performance. We will show that the actual rear side irradiance for an actual, tilted, equator-facing system, with cell-size resolution, varies between 47 and 83 W/m2. Varying distance and position of near-field objects, the drop in current is in good quantitative agreement with the measured reductions in rear side irradiance. Increasing the reflectance of the near-field object strongly reduces the effective shading, the measured loss in rear irradiance and the current drop in the IV curve.