PV cell and module degradation, detection and diagnostics

With crystalline silicon photovoltaic (PV) modules being on the market for over 3 decades, investigation into usual causes and extent of module degradation after prolonged exposure in field conditions is nowadays possible. Degradation phenomena vary significantly between cells, modules and installations, giving rise to different power degradation rates reported. The main defects that have been observed in field aged PV modules, include EVA browning, degradation of the anti-reflective coating, delamination between the glass-encapsulant and the cell-encapsulant interfaces, humidity ingress, corrosion of busbars and contacts, shunt paths, cracks/ micro-cracks in the cell, damage of the glass and the back sealing, and bypass diode failure. This study presents severe degradation effects observed in PV modules operating outdoors for over 20 years. In many of the cases investigated different defects were seen to coexist within the same cell or module, leading to more severe effects of optical/physical, thermal, and electrical degradation phenomena significantly reducing the PV power output. Other modules which exhibited extensive optical/physical degradation showed milder degradation in performance. Detection of module degradation was carried out in this study first through visual inspection and I-V curve analysis. Further non-destructive diagnostic techniques were used such as infrared thermography for the identification of hot spots, that were seen to be mainly linked to resistive busbars and contacts, and electroluminescence imaging for the identification of shunts and other defects. The detection, diagnosis and monitoring of such defects is of great importance for a deeper understanding of the complex ageing mechanisms that take place after prolonged PV exposure in field conditions, and the identification of underlying causes, assisting the early identification of defects and the extension of the energy life of PV systems.