One of the most crucial issues for PV modules is the thermal stability during shading situations.
Principally, the hot spot risk can be attributed directly to the properties of the solar cell. The increased hot
spot risk at cells results on the one hand from local shunts, deformations of the p-n-junction, impurities
and the resistance of the raw wafer material and on the other hand from bad cell processing. The risk can
be reduced by using shorter solar cell strings and by using advanced in-line quality control tools for cell
testing. This work presents the investigation about the operating principle of shadowed solar cells in PV
modules. Thereby a focus is the understanding of the current flow in the dark and in the irradiated part of
the shadowed cell. Finally, by means of this current examination the dissipated power can be determined.
Keywords: Photovoltaic; Hot Spot; Crystalline silicon cells; Reliability
2. Introduction
PV installation density increases, and more systems suffer from shadowing along with the related hot spot
risks. Typical shading situations of PV modules are resulting from antennas, bird droppings, self-shading of
adjacent modules, trees, smokestacks and/or from support structures. Basically, each solar cell has a certain
hot spot risk which causes (under unfavorable conditions) that the cell’s operating point is transferred into
reverse voltage and results in heat dissipation. A typical shadowing situation of a standard multi-crystalline
PV module and the origin of a hot spot are shown in Figure 1.