Experts find increased incidence of module breakage has multiple causes

Cracked glass is a terminal event for a solar module. Allowing water in and current out, a cracked module needs to be replaced, which makes it a serious and urgent concern. A new report published by US experts sheds some light on an increased prevalence of module cracking.

While in recent years, solar technology has consistently progressed towards higher efficiencies at lower cost, glass cracking has become more common. In solar projects on the rooftop or ground mounted, Operations and Maintenance (O&M) providers and field engineers have been reporting cases where glass cracks are visible on either the front or nearside glass.

Interestingly, it is often not immediately apparent what has caused the cracking. Impacts from things like hailstones is an obvious candidate, but the cracking is far more widespread than hailstorms leading solar researchers to look more closely at the problem. And the rapid expansion of large format, dual-glass modules certainly appears to be one of the drivers of the development.

NREL findings

In December 2024, researchers at the U.S. National Renewable Energy Laboratory (NREL) released an illuminating study into the issue, called Tough Break: Many Factors Make Glass Breakage More Likely. And while its findings are not conclusive, they are illuminating.

In the 14-page paper, the solar boffins at NREL report that increased glass breakage is likely a result of multiple factors, and could very well be a number of factors working together to push the module glass beyond breaking point. The potential causes relate both to industry trends, balance of system (BoS) components, and manufacturing processes. And they are all underpinned by solar production’s defining dynamic: more power at lower cost – which is both a blessing and (in this case) a curse.

In summary, the Tough Break findings are:

- Thinner module glass (at 2mm) does not undergo the strengthening processes as thicker (3.2mm) glass in production

- Flaws can be introduced along the glass edge or surface

- The edge of dual-glass modules can become pinched during lamination

- Larger module formats – and they are getting big! – can be more prone to bending or flexing when it’s windy, attracting the term “big floppy modules"

- And, the module frame can contact directly with the glass and dirt/sand ingress can occur

How did we get here?

Before delving deeper into each of the phenomena reported by NREL in their module breakage report, it’s worth looking at the factors that lead to this difficult development. And the relentless pressure on module makers to reduce cost plays a significant role.

Module prices have decreased dramatically in recent years. While that may seem like a windfall for consumers, it should be kept in mind that it means that the companies making the modules are under serious financial pressure. Without naming individual module makers, large losses were commonplace among module manufacturers in 2024 and while there are signs that things are stabilising this year, PV manufacturing remains a business defined by the imperative to find savings wherever possible.

The result is that there is evidence of cost cutting in the factors that NREL found were contributing towards the increase in module breakage. Cost cutting can result in faults on the glass edge, less robust processes for lamination resulting in edge pinching, and a reduction in the amount of silicone used along the module frame meaning the aluminium touches the glass. Each of these factors, NREL finds, can result in faults in the glass or excessive stress, which ends up in cracking.

The shift to dual-glass encapsulation combined with large format modules has also been a big driver, behind the scenes, of cracking. As the era of PERC technology began to draw to a close earlier this decade, module makers generally turned to size as a way to boost power output – rather than next-generation PV cells like heterojunction or back contact. Crystalline silicon cell sizes got bigger, as did modules. This resulted in module formats that are more prone to cracking.

After this move to “bigger rather than better,” the switch to TOPCon occurred. While the adoption of higher-efficiency n-type technology is a positive development, TOPCon cell technology can be more sensitive to moisture – and module makers responded by adopting dual-glass encapsulation. Big modules with dual glass would be both prohibitively expensive and heavy if they used 3.2 mm glass, so 2 mm thicknesses became the norm.

Taken together, it’s almost the perfect storm: dual-glass, bigger module formats, thinner glass, and attempts to cut costs in production. The result has been a big increase in module breakage.

Expert opinion

To delve deeper into the issues, at Baywa Solar Systems we recently got in touch with international module testing and quality experts for a background briefing on the subject. They confirmed that glass breakage is becoming a significant issue.

“We were involved in several glass breakage issues in 2024 and defining an overall valid hypothesis for a root cause may not always be easy,” said one module quality expert. “There can be so many different causes for these thin, only partially-tempered glasses, and obviously many systems show issues.”

Speaking to another expert, they suggested that glass breakage could be linked to O&M, but it was not always the prime suspect. 

“Anecdotally, glass breakage (both front and rear) is an issue affecting multiple module manufacturers with multiple module sizes and multiple mounting configurations in multiple regions. In some cases, it’s an installation or O&M issue (e.g. rocks hitting the modules during vegetation abatement). In other cases, there is no clear external factor and poor module/glass quality is the logical (or only) culprit.”

What to do?

As the NREL study found, there’s no single cause for module breakage and, as such, no silver bullet to navigating the challenge posed by today’s modules. Certainly, working with a major module distributor can provide some protection. Highly skilled quality assurance teams can identify some of the failure causes highlighted by the NREL researchers – including flaws, edge pinch, insufficient silicone sealant, and larger formats that come with insufficiently-robust frames. And quality teams operating in multiple international markets can develop databases of breakage incidents, which can be used to guide future purchasing decisions.

There are also things that can be done by installers to reduce the risk of breakage. Firstly, proper module transportation and handling is more important than ever. Two-person handling reduces the risk of breakage and should be used wherever possible. Avoiding the use of large-format modules for residential rooftop projects is also advised.

For ground mounted systems, the interrelation between module clamps and what can be “big floppy modules” is crucial. Cheaper clamps and flimsy mounting structures increase the risk of movement under wind load and can compound module instability. It may also be worth instructing anyone who will be cutting grass or operating machinery nearby to an array to ensure that gravel or stones are not kicked up against the module glass.

At a recent quality-focused event, one engineer highlighted that it is the interplay between the mounting structure and the big, dual-glass module that is crucial. With pressure also on mounting structure suppliers to reduce the amount of steel that is used or to select lower-cost components, it is important to ensure that the module and its mount is considered together as a system. A “floppy” mounting structure is equally likely to cause breakages as the big “floppy” modules of today.

There is no simple solution to the problem of glass cracking and even precisely ascertaining one cause of the development is equally difficult. There is some hope that as experience using 2mm front and back glass increases that manufacturing, system, and handling efforts will evolve to reduce cracking to a minimum.