Comparative degradation analysis of accelerated-aged and field-aged crystalline silicon photovoltaic modules under Indian subtropical climatic conditions

Abstract

The understanding of the degradation modes in end-of-life (EoL) photovoltaic (PV) modules is essential to develop realistic and effective accelerated testing methods. In this paper, types of defects and degradations (D&Ds) observed in EoL field-aged modules (FAM) have been compared with the accelerated-aged modules (AAM) for their type and underlying mechanisms. For this purpose, the FAM exposed to outdoor environmental conditions for 20 years have been taken from two cities in India. The observed D&Ds in FAM were compared with modules subjected to the temperature and humidity accelerated tests as per IEC 61215-2 standards using visual inspection, electroluminescence imaging, microscopic inspection, and current-voltage measurement. Encapsulant discoloration and delamination were the dominant modes of degradation observed in the FAM from both locations. Further, thermo-mechanical and mechanical breakages were more pronounced qualitatively under accelerated testing conditions. On the other hand, different types of chemical-induced degradations impacting both metallization and interconnects have been observed in varying degrees within damp heat and humidity freeze subjected AAM and FAM. The loss in electrical parameters namely, short circuit current and fill factor has been observed to vary in FAM and AAM subjected to different stress conditions based on the loss incurring mechanism of dominant degradation modes. The comparative analysis highlights the need for the development of effective sequential aging tests which can take into account the actual mix of external environmental conditions responsible for the various mechanism of degradation in the PV modules.