Solar glass is not supposed to break on its own. Increasingly, it does.
Since around 2021, scientists, operators, and testing laboratories have been recording glass breakage on solar modules with no apparent cause such as impacts or extreme weather.
What was once dismissed as isolated incidents has now been confirmed by independent testing laboratories as the single most significant module reliability issue in the global PV industry today, with direct financial and safety consequences for commercial building operators, HVACR-integrated solar installations, and the contractors who specify and maintain them.
The Scale of the Problem
The numbers from independent testing are alarming.
In the second quarter of 2025, Kiwa PVEL’s mechanical stress sequence testing recorded a historic high, with approximately one-third of modules’ glass breaking. In the final quarter of the year, results improved slightly, with roughly one quarter of samples failing. Those are still unprecedented results in decades of commercial module manufacturing.
Kiwa PVEL’s 2025 scorecard indicates that 83% of manufacturers failed at least one module reliability test, compared to 66% in 2024.
The trend is not improving fast enough.
Cases of cracked or broken modules, sometimes just weeks after installation, occur without any external shock or exceptional weather event being implicated.
Spontaneous glass breakage in glass-glass modules is the most significant reliability issue affecting modules today, according to Kiwa PVEL. The laboratory confirmed it is occurring in multiple countries, with multiple module model types, mounted to multiple trackers and racking solutions.
The Root Cause: Cost-Cutting Erodes Safety Margins
The cause is straightforward and industry-driven.
New PV modules in power plants are now larger than ever. With glass on both sides representing more than half of a module’s weight, it is not surprising that manufacturers found room to cut costs by reducing its thickness.
Previous generations of modules used 3.2 mm glass. Most current production uses glass approximately 2.0 mm thick.
Tristan Erion-Lorico, Vice President of Sales and Marketing at Kiwa PVEL, explained the consequence clearly.
“Generally speaking, we have thinned the glass, frames, and encapsulant and gone to more aggressive mounting. That probably all works on paper, where the perfect module should be reliable over the expected lifetime. However, we have eroded the safety margins, and now microscopic defects along the glass edges or surface, improperly placed silicone or frame adhesive, edge pinch, pressure from the busbars, and so on, can result in module breakage.”
The US National Laboratory of the Rockies surveyed contributing factors in late 2024, identifying reduced thermal strengthening in thinner modules, microscopic flaws, lamination-induced stresses such as edge pinch, increasing module size without corresponding mounting changes, and contact between glass and frame or trapped debris.
What the Science Confirms
For a 2026 paper, NLR developed a non-destructive method to measure glass surface stress directly on finished solar panels. Using this method, researchers collected data from numerous mass-produced panels from commercial fields where glass had spontaneously broken.
NLR module reliability researcher Elizabeth Palmiotti summarised the findings directly.
“We confirm that most 2.0 mm glass in PV modules is fully tempered; however, it remains weaker than traditional 3.2 mm glass. Our results show a clear correlation between lower surface stress and increased susceptibility to spontaneous breakage. This is an important consideration for modules that are supposed to survive in various environments for more than 30 years.”
Palmiotti noted that while 2.0 mm glass can meet fully tempered thresholds under certain standards, its surface compressive stress is generally lower, and the compressive layer itself is thinner.
Safety Consequences Beyond Energy Yield
For commercial building operators and HVACR-integrated rooftop installations, the consequences of spontaneous glass breakage extend well beyond lost energy production.
A broken module is no longer a Class 4 live appliance and therefore poses a risk of electrocution to on-site personnel.
Reduced impact resistance also increases breakage during module installation and maintenance, particularly when cutting vegetation with stones, which can damage the panels. In some projects, the breakage rate reaches significant levels, leading to production losses, replacement costs, and safety risks for personnel.
Erion-Lorico reinforced the long-term reliability concern.
“A module that breaks after static mechanical load or dynamic mechanical load tests is likely not going to last 30 years in the field.”
For building owners specifying solar systems with 25 to 30-year performance warranties, that statement carries significant contractual and financial weight.
What Can Be Done
A key solution to edge pinch is using spacers during lamination to ensure uniform glass thickness. The thin-film PV industry has used this technique successfully for decades, but many crystalline silicon module manufacturers still struggle with edge pinch.
Studies have found that contact between glass and frames is linked to spontaneous breakage in some modules. Using rubbery silicone spacers to maintain separation between the glass and the frame can prevent localised stress build-up. Power plant operators should also regularly inspect modules for signs of debris accumulation and clean frames to prevent sand-related abrasion.
Testing for internal stresses after lamination could also help detect modules that are at higher risk of breakage before installation.
The missing piece, however, is standardisation.
Manufacturing pressures and a lack of PV-specific standards are hindering solutions
across the industry, leaving specifiers and operators without a consistent benchmark against which to assess module glass quality before procurement.
The Specification Implication for HVACR and Building Professionals
For HVACR engineers, building services consultants, and commercial property operators specifying rooftop solar as part of integrated building energy systems, this crisis demands an immediate review of procurement standards. Asking manufacturers for mechanical stress sequence test results from accredited independent laboratories, specifically Kiwa PVEL or RETC, before finalising any module specification is now essential due diligence rather than optional caution.
Modules specifying 2.0 mm glass should be evaluated against independent SML and DML test data, not manufacturer data sheets alone. Where long-term warranties are a key contractual requirement, verified mechanical durability testing results must be part of the procurement evidence base.
The solar industry’s cost-cutting cycle has created a reliability deficit that is now visible in the field. The burden of managing that deficit has shifted, for now, to the specifiers, operators, and building professionals who install and maintain these systems on occupied commercial buildings.