Na-free glass for elimination of potential induced degradation

Na-free glass was investigated as a means of reducing or eliminating potential-induced degradation (PID) in c-Si PV modules. Multi-cell and single cell modules, manufactured with glass on both the front and back sides (glass/glass), were biased at -1000V while being subjected to PID-accelerating conditions - 85°C and 85%RH, and 85°C while wrapped in Al foil. Under these conditions, all modules having conventional soda lime glass (SLG) on the front side failed. The use of sodium-free (Na-free) glass on both sides of glass/glass modules eliminated both moisture ingress and PID. Modules with Na-free glass on the front and SLG glass on the back exhibited significant PID resistance compared to modules with SLG on the front. Multicell modules with either glass type on the front, but with conventional backsheets, failed due to moisture ingress under 85°C/85% RH conditions. During the course of the testing, it was observed that shunt resistance was a sensitive leading indicator of PID, decreasing by almost two orders of magnitude before a decrease in efficiency became detectable.