RETC’s 2024 Module Report Flags Rising UVID Risk In n-TOPCon Modules

US based third party Engineering advisory and test services provider Renewable Energy Test Centre (RETC) just put out its 6th annual report, which focuses on solar panel reliability across various factors. Solar panels from multiple manufacturers are run across a suite of testing procedures and graded according to their performance. The modules are then categorized according to their performance in the tests.

The Qualities That Matter (Source: RETC)

1) Ultraviolet Induced Degradation: A high risk in new PV cell technologies, UVID is an irreversible source of damage that might cause panel quality degradation. This testing sequence exposes test samples to 220 kwH/square meter, allowing for conditions similar to leaving the panel for 2.8 years in the field. RETC noted that some of the new cell technologies-most notably n-TOPCon-appeared susceptible to UVID. 40% of the models tested med UVID high achiever criteria, which means that degradation was below 2%. More worryingly, 40% of the panels also returned a UVID red flag result, with 10% to 16% degradation in some products on both sides. Without immediate and collective action, UVID has the potential to become a major reliability issue for industry stakeholders.

2) Thermal cycling: Intended to be used to characterize a PV module’s ability to withstand stresses associated with diurnal and annual temperature fluctuations, the thermal cycling test cycles modules between two temperature extremes- 85 C and -40C. Products that pass this test are given the TC600 certification, which means that they lasted thrice as long as product certification (TC200). The goal of TC testing is to probe module designs for thermal fatigue failure node. These are highly relevant for deployment in areas with wide temperature swings. As of 2024, 67% of models tested met TC high achiever criteria, with 9% returning a TC red flag result. 11 different manufacturers were TC high achievers.

3) Hail Durability: Because the hail durability test is an optional sequence within the Thresher Test program, RETC did not establish a red-flag threshold in this category. To address the gap in the IEC’s standards only requiring modules to withstand a kinetic impact energy of 2 joules, the RETC exposes modules to 45mm diameter freezer ice ball impacts, followed by 50 thermal cycles and hot spot endurance testing. For test category high achiever recognition, RETC required that samples withstand an effective kinetic energy of at least 20 joules. A class-A hail classification indicates that a test sample experienced less than 1% maximum power degradation upon completion of the test without incurring significant visual abnormalities or defects.

4) Damp Heat Resistance: The damp heat sequence in RETC’s test suite tests whether a module is equipped to withstand prolonged exposure to humid, high temperature environments. The modules are subjected to a controlled temperature of 85 C at a relative humidity of 85% for a set amount of time. The DH sequence for the test has a 2000 hour duration, which is twice the duration typically required for product certification. The samples also undergo a modified boron-oxygen light-induced degradation test. DH results have been trending downwards on a year-over-year basis, likely a sign of manufacturers getting loose with tolerances. 26% of the models tested met DH achiever criteria, with 18% of the models tested returning a DH red-flag result.

Yash Singh