Ultraviolet-induced degradation (UVID), a potential reliability concern for TOPCon PV modules under long-term UV exposure, has recently raised concerns among project developers, insurers, and financiers. Although the degradation mechanism has been documented in several reports and early scientific publications, in-house test results from Fraunhofer ISE suggest that the commonly used UV testing process overestimates actual performance degradation.
Motivated by the observed meta-stable behavior of commercial TOPCon PV modules, the lab initiated a deeper investigation into the UV test procedure, including parallel outdoor testing. After destabilization at 60 kWh/m² of UV irradiation – equivalent to one year of UV exposure in Germany – the modules exhibited notable efficiency loss during dark storage. However, subsequent outdoor sunlight exposure triggered a significant recovery effect, according to the lab.
Following the stabilization process, most modules showed minimal degradation, although a few still experienced power losses of up to 5%. Furthermore, a comparison of field data from Fraunhofer ISE’s outdoor performance lab with analyses of returned TOPCon modules at the institute’s CalLab PV Modules validated the updated test procedure. The findings indicate that the revised approach yields degradation measurements much closer to real-world performance.
Overall, Fraunhofer ISE concludes that the actual impact of UVID on TOPCon modules is significantly less severe than what conventional UV tests suggest.
Daniel Philipp, head of the Department for Module Characterization and Reliability at Fraunhofer ISE, commented, “Unfortunately, many module types of the current generation of commercial TOPCon PV modules react sensitively to UV irradiation. This is also confirmed by modules returning from the field and comparisons between modules aged in the laboratory and in the field. However, the degradation rate does not appear to be as drastic as previously assumed.”
He continued, ”We recommend that users test PV modules according to the latest findings. In research, it remains necessary to further analyze the phenomenon to more accurately predict the long-term effects of UV-induced degradation on module yield”.
