Results from an International Interlaboratory Study on Light- and Elevated Temperature-Induced Degradation in Solar Modules

This paper reports the results of an international interlaboratory comparison study on light- and elevated temperature-induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection and screen a large and diverse set of prototype modules for LETID. Results across labs indicate the reproducibility of LETID testing is likely within ±1% of maximum power (P_MP). In intentionally engineered LETID-sensitive modules, mean degradation after the prescribed detection stress is roughly 6% P_MP. In other module types the LETID sensitivity is smaller, and in some we observe essentially negligible degradation attributable to LETID. In LETID-sensitive modules, both open-circuit voltage (V_OC) and short-circuit current (I_SC) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the estimated loss of cell I_SC, which drives loss of module I_SC. Overall, this work has helped inform the creation of a forthcoming standard technical specification for LETID testing of PV modules, IEC TS 63342 ED1, and should aid in the interpretation of results from that and other LETID tests.