Application of the NREL Test-to-Failure Protocol for PV Modules

Initial results of application of the NREL Test-to-Failure Protocol are presented and discussed. Six commercially available multicrystalline Si-cell flat-plate modules were subjected to the protocol with controls. The samples were divided among three test sequences, (1) 1000 hours of 85C/85% relative humidity with positive or negative 600 V bias to the active layers with respect to the grounded frame, (2) -40/85C thermal cycling with electrical load at the rated module power, and (3) an alternating sequence between tests (1) and (2). Application of the protocol manifested in the acceleration of degradation mechanisms seen in the field including backsheet delamination, corrosion, bubble formation within the laminate, discoloration of the antireflective coating, and localized heating with degradation of the backsheet as a result of moisture ingress, corrosion, and concentrated current flow. Significant differences in performance after one round of the protocol are seen in damp heat depending on the polarity of the bias applied to the active layer (the short-circuited power leads of the module). The protocol is found to successfully accelerate module degradation mechanisms that have been observed in the field and will help to differentiate the performance and reliability of various module technologies.