Performance and Reliability Implications of Two Dimensional Shading in Monolithic Thin Film Photovoltaic Modules

TL;DR

This paper investigates how partial shading affects the performance and reliability of monolithic thin film photovoltaic modules, revealing unique shading effects, potential damage risks, and the limited protective role of bypass diodes.

Contribution

It provides a detailed analysis of shading impacts specific to monolithic TFPV modules, highlighting the effects of shadow shape, size, and orientation on module reliability and performance.

Findings

Unshaded parts of shaded cells experience higher heat dissipation.

Thin edge shadows can cause reverse bias damage.

External bypass diodes do not protect individual cells from shadow-induced stress.

Abstract

We analyze the problem of partial shading in monolithically integrated thin film photovoltaic (TFPV) modules, and explore how the shape and size of the shadows dictate their performance and reliability. We focus on the aspects of shading problem unique to monolithic TFPV, arising from thin long rectangular series-connected cells, with partial shadows covering only a fraction of cell area. We find that due to the cell shape, the unshaded portion of a partially shaded cell experiences higher heat dissipation due to a redistribution of voltages and currents in this two dimensional geometry. We also analyze the effect of shadow size and orientation by considering several possible shading scenarios. We find that thin edge shadows can cause potentially catastrophic reverse bias damage, depending on their orientation. Finally, we show that external bypass diodes cannot protect the individual cells from shadow-induced reverse stress, but can improve the string output for larger shadows.