Photovoltaics testing laboratory Kiwa PVEL recently released the 2026 version of its PV Module Reliability Scorecard, which includes eight Top Performer categories that correspond to tests conducted by the laboratory under its Product Qualification Program (PQP) testing regimen.
The Scorecard’s newest top performer category looks at ultraviolet-induced degradation (UVID), a problem that occurs when exposure to high-energy UV photons causes damage in the passivation layer applied to silicon solar cells, which can result in large decreases in the output power of solar modules as they are exposed to UV light in the field.
The mechanism behind UVID has been known for decades, but concerns surrounding about the degradation came to prominence in 2022, because the effects of UVID on solar cells can be particularly pronounced in modern technologies such as tunnel oxide passivating contact (TOPCon) and heterojunction (HJT) solar cells.
Kiwa PVEL has actually been conducting the UVID testing on modules as part of the PQP since 2023, but the organization prefers to use the first few years of a new test to gather and share data with manufacturers. Based on that data, the test lab devises a benchmark for what constitutes best-in-class performance.
For 2026, a top performer in the UVID test is any specific module build (known as a “bill of materials,” or BOM) that displays less than 2% power loss degradation after being subjected to 120 kWh/m² of ultraviolet light, which simulates approximately one year of outdoor exposure.
“Normally, we create a page of the scorecard to share our findings with the industry after a new test is released, so that manufacturers can learn from what we’re seeing and downstream (stakeholders) can understand how much risk is involved,” said Kiwa PVEL vice president of sales and marketing Tristan Erion-Lorico in comments to pv magazine USA. “We want to share our findings, but we (also) want to give manufacturers some time to improve their modules, (so) when calling out top performers, we’re not just saying one or two BOMs or one or two companies were a top performer in that new test.”
For 2026, Kiwa PVEL recognized 91 individual solar panel models (also known as “bills of materials” or BOMs) as UVID top performers, representing 19 of the 43 manufacturers whose modules were submitted for UVID testing.
Dark storage degradation
In addition to helping manufacturers understand the factors that lead to better performance in a new test, the waiting period before incorporating the test as a top performer category gives Kiwa PVEL a chance to examine and refine its test methodology to be sure it is fairly assessing module quality.
For example, in looking through the results of its past UVID tests, Kiwa PVEL engineers discovered that modules continue to lose significant power as they sit in storage after being subjected to UVID testing.
In the example shown above, the leftmost image shows a module’s performance under an initial “flash” test to determine its power output characteristics. The next image to the right shows that the module displayed 4.5% power degradation after the UVID sequence, and the third image shows how a flash test revealed an additional 4.4% of degradation after a period of dark storage.
The final image in the example displays the result of a flash test conducted after the module had been exposed to a short full-spectrum light soak for 0.1 kWh/m² under open-circuit conditions, essentially mimicking a brief period in the sun. The module recovered some of its lost performance, but at 4.3%, degradation was still more than double the limit necessary to qualify as a top performer.
Findings like these led the Kiwa PVEL team to develop a new standard of testing in which modules must be flash tested within 48 hours of their UVID sequence. The 48-hour threshold allows for testing that more accurately portrays a module’s performance.
Furthermore, not all modules are equally susceptible to dark storage degradation. The ones that are will be those that already exhibit higher UVID within the 48-hour period.
“If the module is generally UV stable, it’s also more or less dark storage stable,” said Erion-Lorico. However, he said, “if you see, for example, 5% UV degradation, you might see 10% after a few weeks in dark storage. That dark storage power loss is greater on modules where the UVID power loss was greater.”
Kiwa PVEL and pv magazine USA webinar
Topics like UVID and all the other PQP top performer categories will be discussed in an upcoming webinar: Evaluating solar module reliability: Inside the Kiwa PVEL Scorecard.
Tristan Erion-Lorico will join pv magazine USA editors Ryan Kennedy and Ben Zientara to discuss how major differences in module performance are shown through the PQP testing process, focusing on the most prevalent causes of module failure, including breakage, delamination, and Ultraviolet-Induced Degradation.People interested in attending can register for free at the webinar page.
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