Defects and fault modes of field-aged photovoltaic modules in the Nordics

Abstract

PV module durability and reliability influences its efficiency and return on investment. Hence, collection of ample and credible PV module reliability data in each climatic zone becomes increasingly essential. In this work, defects and fault modes of field-aged multicrystalline silicon PV modules installed outdoors in Grimstad from 2000 to 2011 are investigated. The investigations were done using visual inspection, current–voltage characterization, temperature coefficient profiling, ultraviolet fluorescence, electroluminescence, infrared thermal imaging, and SEM-EDS analysis. Most PV modules show signs of microcracks, moisture ingress, corrosion, potential induced degradation, optical degradation, and irregular temperature sensitivities. Oxidized silver, tin, and lead were observed in the SEM-EDS results, which confirmed the remnants of moisture ingress. On average, the modules show power output of 78% and their efficiency dropped from 13% to 10%. The average temperature coefficient of efficiency of the module was found to be ca. -0.5%/°C, corresponding to an average degradation rate of 1.09 %/year over the 20 years period. However, the annual degradation rates when the modules were in the field and indoors were 0.98% and 1.33 %, respectively. It is believed that limited evaporation of activated volatile carboxylic products under indoor conditions led to the formation and accumulation of carboxylic acids, hence higher rate of degradation. Moisture induced degradation (MID) mechanisms was the root cause for the overall degradation in the PV modules’ power output, especially over the later years.