Early Detection of Module Faults in PV Systems Caused by Defective Backsheets

Recurring inspections of photovoltaic (PV) systems have revealed a significant increase in module defects caused by the backsheets in recent years. Abnormalities in backsheets, such as chalking, delamination, cracking, or browning, usually lead to a failure of the insulating properties and thus pose a safety risk.

While existing standards and regulations for safety testing mainly focus on the function of new products and research is working to prevent long-term faults in the future by intensively investigating the aging behavior of films and embedding materials, there is a lack of standardization documents that address the acute problems of backsheet quality in existing PV systems.

In Germany, approximately 60 GWp of PV systems are currently connected to the grid, a large proportion of which are now over five years old and are increasingly showing abnormalities in the backsheet. Some of the abnormalities observed are currently only cosmetic in nature, while others pose an inherent electrical risk as live parts are exposed. In addition to electrical safety, a defective backsheet can also lead to significant yield losses due to the shutdown of system components.

However, there is a lack of recommendations for action in the form of standardized rules and criteria regarding defective backsheets. The ANOMALOUS project addresses precisely this shortcoming.

The investigations carried out as part of the ANOMALOUS project aim to close the existing normative gap in the evaluation of backsheets in the field and to establish standardized criteria for the evaluation of anomalies.

The project focuses on the development of a VDE application rule and a standardization proposal that define criteria for evaluating older PV systems and provide recommendations for action for experts and maintenance companies. The resulting catalog of anomalies will also provide greater legal certainty in the individual steps of the value chain. In addition, the research results will be made available to the PV film market so that the service life of PV modules can be significantly increased, thereby contributing to a reduction in the CO₂ footprint required for the manufacture of new modules.

The project work resulted in the VDE SPEC 90027 “Guideline for the evaluation of PV modules with defective backsheets.” It provides guidance for the evaluation and recommended actions for anomalies in PV module backsheets. In addition to visual evaluations, analysis methods and possible electrical safety tests for in-depth evaluation are proposed. The VDE SPEC contains recommendations for experts and maintenance companies. The resulting catalog of anomalies will also provide greater legal certainty in the individual steps of the value chain. In addition, the research results will be made available to the PV film market so that the service life of PV modules can be significantly increased, thereby contributing to a reduction in the CO₂ footprint required for the manufacture of new modules.