No matter how many new ideas or versions of solar PV technology come out, everything ultimately depends on how reliable the solar module is – and that’s the part most at risk when prices drop sharply, as is the case now.
At the TaiyangNews Reliable PV Module Design 2025 Conference on November 6, 2025, top manufacturers and experts met to discuss how to ensure modules remain dependable through good design.
This edited panel transcript highlights their discussion on how new cell technologies and module designs, in a highly competitive market, are putting pressure on today’s reliability standards. The panel was moderated by TaiyangNews Head of Technology Shravan Chunduri, and included Fraunhofer ISE’s Head of Group ‘Degradation Analysis and Modelling’ PV Modules Ingrid Haedrich, GCL’s Technical Support Director - Europe Rojen Malachi, and Jietai Solar (JTPV) R&D Manager Xinrui An.
TaiyangNews: Are today's global reliability standards keeping pace with the speed of innovation in solar PV technology, or are we reaching a point where standards are starting to follow rather than lead the technology?
Ingrid Haedrich (Fraunhofer ISE): I’m not sure standards have ever really been ahead of technology. New tech usually hits the market first, and the standards take quite a while to catch up. For example, when backsheet problems started showing up, it took about 5 years from the first field issues to updating the standard with the sequence B test. So yes, standards tend to lag, but we’re actively working in the IEC groups to move things forward. Right now, there’s a lot of focus on updating the UVID IEC standard, and the whole industry, including us and all major test labs, is involved to make sure it works not just for TOPCon but also for heterojunction (HJT) and other technologies.
Rojen Malachi (GCL): I agree with Ingrid. Standards have usually lagged behind because the market pushes new technologies for profit, while standards bodies don’t work that way. They also can’t just stop companies from selling or buying certain modules; that’s not how the economy works. At GCL, we work closely with labs like TÜV Rheinland on qualifying our modules, and through that, we stay connected to the committees and understand what to expect and how to meet upcoming requirements.
Xinrui An (JTPV): I agree with Ingrid and Rojen that standards can fall behind products and technology. But I also want to add something. Take UV issues, for example: they aren’t very serious for aluminum BSF or PERC cells because their heavily diffused surfaces provide strong field-effect passivation, not just chemical passivation. But for newer cell types like TOPCon and HJT, the surfaces are only lightly diffused, so any damage to the chemical passivation has a much bigger impact. In these cases, it’s not just that standards lag technology; it becomes a loop where improving the technology creates new reliability problems, and then you need to study those mechanisms further.
TaiyangNews: Since UVID was first discovered in HJT, why wasn’t it tested for or detected earlier in TOPCon, especially when we already knew to watch out for issues like LID, LETID, and PID from PERC?
Rojen Malachi (GCL): UVID is already included in IEC 61215 with 15 kWh of UV exposure, but that level isn’t enough to reveal these defects. They only start to show up around the UVID 60 level. For us, UVID 60 is a good balance between realistic conditions and what’s practical in terms of time and cost for qualification.
Ingrid Haedrich (Fraunhofer ISE): Even though we knew about metastabilities, early on, people simply put a module through a UV 60 test and measured it straight after, without realizing light soaking was needed in between. That created confusion because the results mixed up metastability effects with real UV degradation. PERC didn’t show this issue in the same way. We only saw the problem so clearly because we extended the usual IEC sequence and measured after each step – after UV, after HF, and after UV again. Standard testing doesn’t include these intermediate checks, so normally you’d only see the start and end results. People check more now, but you still can’t design tests for every possible scenario.
TaiyangNews: Indoor tests sometimes seem tougher than real outdoor conditions, as shown in the Fraunhofer study you (Ingrid) mentioned, where the degradation patterns weren’t the same and indoor tests looked slightly over-engineered. Should we be worried that we’re over-testing? Or is it better to keep these stricter UVID test protocols to stay on the safer side?
Ingrid Haedrich (Fraunhofer ISE): Accelerated testing has always been tricky. We need to speed things up because we can’t wait a full year of outdoor exposure, so we push the modules harder. That naturally raises the question of how realistic the conditions are, like the long-standing debates about Damp Heat 1000 and whether its temperature is too high. If we lower the stress, the test takes much longer, which isn’t practical. So, we try to stay as close as possible to outdoor conditions while still keeping the timeline short.
Even if 60 kWh of UV is a bit higher than what a module sees in a year, the test is still useful because it lets us compare many module types against each other. Standards aim to provide a common benchmark, not to perfectly replicate every environment. But if a test becomes so harsh that a material fails indoors even though it would survive in real outdoor use, then the test isn’t doing its job. That’s why we sometimes adjust our procedures depending on the module design. We know what’s realistic, we know what the standard expects, and we try to bridge that gap for the specific material combinations we’re evaluating.
Rojen Malachi (GCL): From a module maker’s perspective, there are countless ways a module can fail, but the real question is which tests actually matter for the customer. If you know a project site has certain conditions, like high elevation or strong UV exposure, you can extend specific tests, such as UVID, to match those risks. The idea is to focus on the reliability tests that are relevant for that environment, instead of trying to test every module for every possible failure mode beyond the standard IEC 61215.
Xinrui An (JTPV): What matters for us as a manufacturer is that even if these exaggerated stress tests sometimes ‘overkill’ a product, they push us to understand the underlying mechanisms. Today’s cell types, like TOPCon, HJT, and BC, have very different surface structures compared to older designs. And when we compare their UV results, the differences are clear. This helps us think about what’s causing those differences and guides us toward designing products that aren’t just more efficient but also more stable and better-engineered overall.
TaiyangNews: In short, if we use down-conversion films that turn UV light into visible light, like the ones shown in the HANGZHOU FIRST presentation, does that fully solve the UVID issue in TOPCon modules? Or is it not that straightforward, and are there still potential hidden UVID risks even with such materials?
Ingrid Haedrich (Fraunhofer ISE): UVID is pretty well understood now, and TOPCon modules already react better to UV than before. But if you change the module design, like adding down-shifting materials, you also introduce new questions. The polymers in the encapsulation might age differently under UV, so you may need extended UV tests to see how stable they are. And if you tweak the cell design or layer stack, it could lead to other unexpected effects, too. So, every design change means you have to test again in a slightly different way. Overall, though, testing over the past year shows clear improvement in TOPCon UV performance. The only challenge is that older data from 2 years ago can't really be compared, because those measurements weren't stabilized the way they are now.
TaiyangNews: Rojen, as an integrated manufacturer, what part of your internal qualification process is now more demanding than the formal certification part?
Rojen Malachi (GCL): For every new product or cell architecture, we don’t just rely on the standard IEC certification; we go beyond it, usually doing 2 times IEC 61215 tests like Damp Heat, Thermal Cycling, PID, and sometimes even three times. For issues like LETID, we test n-type cells for 324 hours. We also run salt-mist tests up to class 8 and include dynamic mechanical load testing, even though that’s not part of IEC.
On top of that, we carry out power measurement round-robins with a golden reference module to ensure the power we claim is the power customers actually receive. We test packaging too, because it matters for long-distance shipping, and we participate in PDEL qualification testing.
All of this is necessary because offering a 25–30-year module warranty is a huge commitment; if we fail on reliability, we lose money. So, our internal tests have to be tougher than the formal certification.
TaiyangNews: In your presentation, you showed GCL’s carbon data platform, which tracks carbon information across the entire value chain. From a reliability and warranty standpoint, how can this platform actually help improve or support module reliability? Could you explain how it works in that context?
Rojen Malachi (GCL): We launched our carbon data platform a little over a year ago, so it’s still quite new. But from a traceability point of view, it already helps us find the root cause of a problem much faster. If there’s ever a serial defect in the field, the biggest challenge is quickly understanding what went wrong. Normally, you’d rely on flashing or standard tests, but those can take time. With full traceability across the value chain, we can narrow down the cause much sooner.
The second part is AI. We’re already testing AI tools in our cell production lines and plan to bring them into module manufacturing next. In the future, when there’s a warranty claim, this combination – field data, manufacturing data, and AI-driven analysis – will let us identify the root cause much more quickly. All the data feeds into one loop, helping us respond faster and more accurately.
TaiyangNews: Xinrui, are you seeing any new or increasing degradation signatures at the cell level that are specific to TOPCon and not fully covered by today’s testing protocols? Anything you think should be added or emphasized more going forward?
Xinrui An (JTPV): In general, our current protocols already address most cell-level issues. But with today’s cell technologies, the focus may need to shift. UV is one area, and we’ve talked a lot about that. Another, in my view, is damp heat. High-efficiency cells now use pastes with very little aluminum, which is good, but the newer silver pastes are also becoming less corrosive to boost VOC by a couple of millivolts. That’s attractive for manufacturers, but it also means the paste doesn’t penetrate the silicon nitride the way older pastes did, which could make DH more of a concern. There’s a limit to how low you can push corrosivity. So, I’d say UV and DH are the 2 mechanisms we need to stress more in the current protocols.
TaiyangNews: And a quick follow-up. Bo from HANGZHOU FIRST mentioned that cell design and paste choice are crucial when selecting encapsulation, but module makers who buy cells don’t control those aspects. Do you work closely with such module makers and help them choose the most reliable BOM? How does that collaboration look?
Xinrui An (JTPV): Yes, we do. When we develop a new cell architecture or a new material like silver paste, we run the cell-level tests in-house – LID, LTID, UV, and so on – but we also need to see how it behaves in a full module. So, we work with regular module partners, we send them our new products, they build modules with their standard BOM, and then test for UV, DH, and anything relevant. They share the results with us – whether the modules pass or fail – and based on that, we decide whether the new product is ready to be introduced more widely.
TaiyangNews: Rojen, in your presentation, you mentioned that using multi-cut cells – not just half-cut, but 2-, 3-, or 4-cut – can lower the current and therefore reduce hotspot temperatures. Do you have any early results or even a rough idea of how much the hotspot temperature drops?
Rojen Malachi (GCL): I’d need to check the exact numbers, to be honest. I can’t give you a figure right now.
TaiyangNews: That caught my attention because Heng from LONGi noted that starting from around 110°C, the reduction could be almost 50%, maybe somewhere in the 40–50% range. That’s significant. So, if someone sticks with the same technology but adds multi-cuts and still manages to bring down hotspot temperatures that much, it would be a big win.
TaiyangNews: Ingrid, you spoke about glass and the many uncertainties around these circular cracks. At the same time, glass itself is a broad topic: tempered glass, coated glass with different layer stacks, and even polymer alternatives replacing glass. Are all these variants on your radar for evaluation, or are you already stretched with the issues you’re currently investigating?
Ingrid Haedrich (Fraunhofer ISE): We’ve seen a huge rise in glass-related claims and failure analyses in recent years, and the trend isn’t really settling. Sometimes the cause is obvious, like clamping or mounting issues. But when we get modules with those circular crack patterns, where we may or may not find a glass impurity, the root cause becomes much harder to define. There’s simply no dedicated test for that yet.
Right now, we still can’t clearly distinguish between different glass manufacturers or glass quality levels through our standard tests. That’s something we’d like to achieve, and we’re working toward it, but we’re not there. Glass quality is generally assessed through destructive methods – bending tests, double-ring tests – on large samples of glass sheets. In a PV lab, we only receive a few finished modules, so we’re very limited in how deeply we can assess glass quality. We’re improving, but the constraints are real.
Another challenge I hear from EPCs is the field side: once modules start cracking, identifying and replacing them is extremely costly, especially in Europe. Technicians have to inspect modules one by one, and these cracks are tiny, not the big, obvious break patterns. So, we’re also working on methods that could support detection in the field.
We’re trying to set up projects with glass manufacturers to better understand what can be done on the production side. But overall, glass quality is a huge topic, and I don’t envy module producers who have to manage this complexity right now.
TaiyangNews: If you had to recommend only one additional test that should be added immediately to the current IEC qualification for new n-type cells worldwide, which test would it be?
Ingrid Haedrich (Fraunhofer ISE): I’d align with the comment mentioned in the chat: I’d focus on glass quality. We’re developing a low-impact test – not a full mechanical load, but a small load combined with a light impact – to help quantify glass quality. That’s something we’re actively working on, and we’re looking for partners. So, if anyone is interested, feel free to reach out.
Rojen Malachi (GCL): For me, it’s not specific to n-type – this is a general wish – but I would add glare and glint testing to the IEC standards. At the moment, everything relies on ISO 9050, and it’s not written with PV modules in mind, especially for applications near airports, highways, rail lines, and so on. There’s a lot of confusion because we have IATA guidance, ISO rules, and then country-specific rules. I think it’s time for a dedicated IEC standard for glare and glint.
Xinrui An (JTPV): From the cell side, I think most things are already covered. I just want to emphasize that we need to make sure that all existing test types are still fully satisfied. We shouldn’t assume that a degradation mode we solved in the past will never come back; new cell structures or new module materials could cause old issues to reappear. So, we need to keep checking everything.
TaiyangNews: Great, thank you. So, to sum up: at the cell level, the testing seems well in place. And at the module level, the main focus is clearly on glass – its quality and its optical behavior. A very fitting closing remark. Thank you.
The complete panel discussion video is available on the TaiyangNews YouTube Channel.