Damp Heat Test on TOPCon Modules Made with Glass/Backsheets

Given the rising market share of TOPCon cell technologies, where the typical PV module configuration is Glass/Glass, there is a need to prove that also Glass/Backsheet can be considered as a valid alternative in terms of performance and reliability. On the one hand these backsheets need to have a high resistance towards water ingress; a factor which gains increasing importance with latest developments in cell technologies like TOPCon which are assumed to be more sensitive to humidity.[1] On the other hand, experience with a couple of premature field failures of modules which were equipped with certain backsheet types [2] suggests to investigate the reliability of backsheets combined with different BOM towards environmental stresses with a common test procedure following the existing standards. In order to test for the general backsheet durability, 8 modules have been tested in a standardized (IEC61215, MQT13) damp heat test (1000 h) in the TestLab PV Modules at Fraunhofer Institute for Solar Energy Systems ISE. The modules were built by two third-party module manufacturers. The module compositions are depicted in Table 01 and Table 02. The test consisted of a total of 1000 h damp heat exposure, The difference between the modules was the encapsulant supplier both being POE based. The aim was to understand differences in PV modules performance that might arise from various material combinations and different production process. At the end of the test all PV modules except one passed the test, remaining below the 5% power loss limit according to IEC 61215. The Glass/Glass module obtained the best result with only 1.68% power loss. The Glass/Backsheet modules power loss was between 3.0 % and 4.3% for all PV modules except one. In addition the backsheets employed remained clear and free of cracks. Only one module lost more then 5% but it is likely that the higher degradation of this module was not due to the backsheet, but rather associated with the difference in encapsulant. Another possibility could be a variation in module manufacturing quality.