THE DESIGN OF HOTSPOT RESISTANT SHINGLED PHOTOVOLTAIC MODULES

Abstract

The shingled module has become an attractive interconnection architecture for its higher packing density and superior power generation. However, with longer strings and smaller cell areas, the modules are particularly vulnerable to developing hotspots from shading elements. In this dissertation, the author develops a framework for the design of hotspot and shading resistant shingled modules. The thesis investigates the susceptibility of shingled modules to higher hotspot temperatures and greater power loss during shading. A case study using commercially purchased shingled modules shows that not only can the architecture develop higher hotspot temperatures (up to 145 °C) than conventional modules, but that secondary hotspot sites can form in unshaded cells at parallel strings. From a study identifying the effects of illumination on reverse bias behavior in popular cell technologies, it was found that p-type cells in particular display an increase in leakage current when subject to illumination. As such phenomena is not currently accounted for in reverse breakdown models such as the widely used Bishop’s equation, a novel split-cell approach is proposed which sufficiently captures the observed light-induced effect.

Based on these findings, an electro-thermal model of a shingled module under variable shading is developed. After experimental validation through specially fabricated shingled modules that allow for string-level measurement and analysis, the model is used to perform stochastic Monte Carlo simulations to examine the relative influence of cell electrical characteristics on power loss and cell heating. Further investigation on cells with illumination dependent reverse breakdown shows the detrimental effect of this light-sensitivity where higher hotspot temperatures can develop. Module level parameters are also investigated where the interconnection architecture and cell fraction are studied in relation to their impact on shading response. Finally, these findings are condensed onto a design matrix which defines the parameter space within which module manufacturers may configure shingled modules such that hotspots do not exceed a set threshold temperature. Such an approach provides manufacturers with the flexibility to create shingled interconnection schemes based on their preferred cell technologies and module characteristics while ensuring that the shingled modules maintain operation under safe and reliable conditions.