Magnetic Field Imaging (MFI) of Shingle Solar Modules

Abstract

Within the last years, a new characterization method for solar modules called Magnetic Field Imaging (MFI) has been introduced. MFI reveals the strength as well as the direction of currents flowing within solar modules by analyzing the magnetic field distribution and thereby allows to trace back electrical defects. Within our work, we demonstrate how MFI can be exploited to characterize solar modules that contain stripe-like solar cells interconnected in a roof tile manner - so called shingle solar modules. In comparison to conventional solar modules, shingle modules yield the potential for higher power densities, exhibit a more homogeneous appearance and are less prone to power losses when being partially shaded. Due to these advantages, shingle solar modules are expected to gain a growing share of the solar module market within the next years, reaching 11% by 2027. As we demonstrate, MFI allows to detect different defects that are typical as well as unique for shingle solar modules, namely a local shunt by smudged electrically conductive adhesive (ECA), a systematic tilt between individual shingles, and locally poor shingle interconnection. Each defect type shows a fingerprint-like characteristic within MFI measurements and thus can be identified without ambiguity. Compared to electroluminescence (EL), MFI tends to display the defects more prominent and clearer. Furthermore, we demonstrate that MFI can be used to study the response of shingle modules to partial shading and observe that the module current bypasses shaded regions, as predicted by theory. We conclude that MFI would allow to investigate any kind of module under partial shading revealing the current flow through the solar cells, the connectors, and the bypass diodes.