Experimental Evaluation of Performance Drop for Crystalline Photovoltaic Modules Affected by Snail Trails Defect

The understanding and quantifying of photovoltaic (PV) modules degradation is important to ensure their lifetime at harsh conditions. A test campaign on several pc-Si PV modules at semi-arid climate has been conducted after 3 years of outdoor exposure. As a result, 58,5% of modules showed snail trails formation. This defect has been observed increasingly during last decade whereas; the performance variation functions of snail trials have not yet been thoroughly investigated. In this work, the power drop of PV modules affected by this defect after 3 years of operating was performed. Besides, electrical parameter degradation is quantified by measuring the modules performance parameters under standard test conditions as a function of field exposure time. The degradation rate (Rd) for each PV modules have been analytically calculated with discrete data. Results show that the rate of power drop of studied PV modules could reaches 3%/years. EL imaging technic also conducted and demonstrates that the snail trails defect occurs at the micro cracks and can be considered as a simple way to its detection. In addition, 0,12%/y of yearly power drop may be due to both snail trails and cracks defects.