The effect of backsheet repairs on insulation resistance in photovoltaic modules

Abstract The degradation of the back sheet layer in photovoltaic modules has emerged as a critical issue, particularly in modules produced around 2010, drastically shortening their operational lifespan. This issue was not initially anticipated, as the materials used in back sheets, such as polyvinyl fluoride and polyethylene terephthalate, were considered durable. This degradation can lead up to the disconnection of entire photovoltaic strings due to safety concerns, causing considerable production losses. Previous studies have largely focused on accelerated laboratory testing, however, real-world conditions and short-term assessments of repair effectiveness have been insufficiently addressed. To fill this gap, our study examines the impact of field repairs using polysiloxane gel on the insulation resistance of photovoltaic modules with degraded back sheets. The experiment involved testing four photovoltaic modules, manufactured in 2010, that showed signs of back sheet degradation. Various repair methods were applied, including partial and full coating with polysiloxane gel, while one module was left unrepaired for comparison. Our findings demonstrate that fully repaired modules showed a substantial improvement in insulation resistance, maintaining values above 200 MΩ, whereas unrepaired modules exhibited significant drops below 10 MΩ during periods of high humidity. These results suggest that field repairs, particularly those using polysiloxane gel, can effectively restore insulation resistance and extend the functional lifespan of photovoltaic modules. Our results not only confirm the positive impact of these repairs on insulation resistance but also highlight the need for further long-term evaluations to fully assess the durability and reliability of these solutions over several years. Graphical abstract