Laboratory experimental analysis of crystalline silicon photovoltaic module degradation after operating over 6 years: A case study in Ghana

Abstract

This paper systematically analyzes and evaluates the performance of photovoltaic (PV) modules after six years of outdoor exposure in Winneba, Ghana, under a hot and humid climate. Unlike conventional field tests, all data were obtained through rigorous laboratory testing conducted on the PV modules and their materials in accordance with IEC 61215 standards to investigate the causes of power degradation. The results indicated an average power degradation of 35.36 %, equivalent to an annual degradation rate of 5.89 %. Although most modules met the wet insulation test criteria specified by IEC 61215, they exhibited potential safety risks for future field operations due to wet insulation values approaching the standard threshold of 24.5 MΩ. The primary cause of power degradation was identified as potential-induced degradation (PID), with modules experiencing power losses of 44.60 % and 99.57 % under PID testing with a 1000 V negative voltage stress. Electroluminescence (EL) images showing dark edges provided strong evidence supporting the presence of PID. Additionally, poor peel strength test results suggested a risk of delamination, which could be attributed to ion migration during the PID process. Four out of five tested module gel contents were comparable to those of typical unexposed ethylene–vinyl acetate (EVA), and two modules still met the standard requirements even after exposure to damp heat (DH1000), indicating that EVA degradation may not be the primary cause of power loss. The water vapor transmittance rate (WVTR) of the module backsheets, after six years of outdoor exposure, continued to meet the requirements of the Chinese National Standard, further suggesting that moisture ingress may not be a significant contributor to power degradation. This study represents a valuable effort to assess the long-term performance of field-exposed PV modules using accelerated aging tests conducted according to IEC 61215 standards.