Lessons from Field Forensic Investigations
Do the up-front cost savings associated with PV module value engineering efforts come at the expense of reduced resilience to field conditions of use? To find out, we interviewed an expert in failure mode and effects analysis.
RALF SCHULZE, SOLEN ENERGY
Ralf Schulze manages field forensics services for RETC. A 15-year veteran in the renewable energy sector, he has worked as a managing engineer at Kaco new energy and Yingli Green Energy Americas and as a quality manager for Sunrun. A renowned source for end-to-end renewables technology problem-solving and specialized services, Schulze is an expert in quality assurance, failure mode and effects analysis, system diagnostics, and corrective and preventative maintenance.
RETC: What is your experience with glass breakage in fielded PV systems?
RS: Glass breakage in the field is not necessarily a new phenomenon. Over the years, we have documented glass breakage in utility solar due to terrain issues, sinking piles, construction errors, installers using impact tools, and incorrect torque settings—the list goes on and on. Having said that, my personal experience suggests that the leading causes of glass breakage may be changing over time as PV modules become larger, using thinner glass and reduced frame profiles. In more recent glass breakage investigations, we are seeing signs pointing to the glass itself, which is not fully tempered anymore.
RETC: How does module glass specification impact project durability?
RS: Laboratory testing clearly indicates that thin, heat-strengthened glass has higher breakage and failure rates as compared to fully tempered glass. While thinner glass may be an ideal way to keep module costs and weight down, there may be other considerations to balance, especially with large-scale modules. Stress on module glass in the field is substantial, especially in the east and west corners of the array under certain wind or weather conditions. While these environmental stress factors have always been there, they were not the leading cause of glass breakage. Today, we are sometimes being called to investigate glass breakage at sites where modules seem to be failing under normal conditions of use. While I have not seen that many impacted sites, a lot of people within the broader community are seeing similar problems. We know this because NREL and DuraMAT share information regarding field failures relatively quickly. For the few sites I have investigated—which are large utility projects on the order of 100 MW–300 MW in capacity—we are seeing spontaneous glass breakage rates of 2%–5%.
RETC: Is there a typical field forensics process for investigating glass breakage?
RS: When we want to pinpoint a root cause, the first step is to isolate each individual problem, starting with the terrain, tracker, installation process, mounting hardware, torque settings, and so forth. Then we start to look for patterns. Is the glass breaking at the mounting rail locations? Is the glass breaking during the installation process or after the commercial operations date? Has the site experienced a severe weather event and been subjected to pressure ratings beyond the allowable design loads? When there is a pattern that repeats itself—either across a site or based on experience—we can identify a particular issue as the likely root cause. When breakage patterns are random, that could suggest the glass itself is not suitable for the specific installation environment. In other words, if we see breakage inconsistent with anything we have seen in the past, it could be because the glass is not fully tempered.
“When breakage patterns are random, that could suggest the glass itself is not suitable for the specific installation environment.”
RETC: Who is most impacted by spontaneous glass breakage?
RS: The parties feeling the pain tend to be the EPC, project owner, or whoever builds the project and then wants to transfer it to a final owner. If glass breakage is documented during the commissioning and handover process, it leads to bigger questions. People will ask, “If spontaneous glass breakage is happening to some modules now, won’t it happen to the other modules, too?” This type of scrutiny is uncomfortable for the module manufacturer, who will generally try to help mitigate the problem. From professional experience, I believe PV module manufacturers are aware of these issues, and I suspect some manufacturers are starting to rethink module construction practices.
RETC: How can laboratory testing help prevent these problems?
RS: There are many aspects to this type of technical due diligence. First, you need to investigate and fully test the resiliency of the glass, especially with ultra-largescale module designs. Hail durability testing is the most likely to identify vulnerabilities associated with the glass itself. Importantly, this testing must exceed the minimum standards for product certification. Second, you need to understand how module frame and tracker mounting rail details impact module resilience to glass breakage. Static and dynamic mechanical load sequences are useful for investigating module glass vulnerabilities related to the frame and rails. This type of testing has consistently shown a tremendous decay in load-bearing capacity whenever module frame profiles drop below 35 millimeters [1.38 in.].
“Once you have qualified vendors and identified resilient BOMs [bills of materials], you need to verify that the product leaving the factory matches one of the BOMs you have locked down.”
RETC: What additional due diligence measures do you recommend?
RS: Ideally, laboratory testing is done as part of a systematic vendor qualification program that starts with long-term durability testing—such as RETC’s Thresher Test—followed by 12 to 18 months of in-field monitoring. Once you have qualified vendors and identified resilient BOMs [bills of materials], you need to verify that the product leaving the factory matches one of the BOMs you have locked down. So if you are building a 1 GW project over a period of years, you need to require monthly BOM verification inspections and ongoing random sample testing to ensure the product you approved is being delivered to the field. Once the product reaches the project site, look for smart ways to improve installation practices as modules increase in area. For example, you may be able to optimize installation quality using robotic suction-cup machines for module handling.
This interview with Ralf Schulze originally appeared in the industry trends section of the 2024 PV Module Index Report.
