Common misinterpretations of thermal signatures on polycrystalline PV modules under different operational conditions

Abstract

Thermal Infrared (TIR) images may be misinterpreted due to the dynamic nature of the operational current–voltage (I-V) and thermal characteristics of photovoltaic (PV) cells and modules. This study investigates and analyses the I-V and thermal characteristics of polycrystalline PV modules to understand the behaviour of abnormal thermal signatures (hot cells) under varying operational points on a module’s I-V curve. A change in operational conditions influences the operational voltage points such that the mismatched cells behave differently under changing load conditions, varying irradiance and partial shading. Mismatched cells can operate in reverse bias and cause abnormal thermal signatures when the module’s operational voltage is less than the maximum power voltage(VMP), 24 V. The mismatch becomes more significant when the operational voltage is 0.2 V, close to short circuit conditions. Cell partial shading of < 10% results in dynamics of the abnormal thermal signatures and can mislead decisions during TIR imaging inspections when bad cells do not show abnormal thermal signatures on TIR images. Carrying out TIR imaging on clean PV modules operating at < VMP will enhance mismatch and the bad cells can show as hot cells, unlike when operating at > VMP. Under low irradiance of < 600Wm−2, mismatched cells can easily emerge on TIR images, however, at irradiance levels > 600Wm−2, only cells having large isolated parts will cause significant mismatch and appear hot on TIR images. This study advances the understanding of the dynamics of operational I-V points and thermal signatures and can improve the operation and TIR imaging inspections of PV modules.