SOLAR VS HAIL: PIVOTING AWAY FROM DANGER
Understanding Why Solar Farms are Vulnerable to Damage from Hail
PV Module Trends
Beyond the fundamental characteristic of all PV modules being encased in potentially breakable glass, recent advancements in PV module technology have inadvertently increased hail vulnerability. Many utility-scale projects today are opting for larger-format PV modules (e.g. 72 or 144-cell, 1 x 2m or 2 x 2m respectively) with thinner front glass—most commonly 2mm thickness for primary reasons of weight and cost reductions.
There are two primary PV module constructions:
Monofacial
The more conventional PV module design, featuring a front-glass and polymer back-sheet, which represents the majority of global installed PV modules. Traditionally, thicker front glasses >3mm have been used, although thinner glasses in the range of 2-3mm are now the most common[1].
Bifacial or dual-glass
This higher yield PV module option can absorb light on both sides, which is why it has growing traction particularly for utility-scale, with a market share of 90% in 2024. This share is anticipated to remain stable for the next 10 years[1]. Given the increased weight associated with dual glass, thinner 2mm glass on both sides is the most common configuration.
Current research and situational evaluation between these configurations to withstand hail impacts and accompanying wind loading is not developing at the pace of the solar PV capacity deployment. This is complicated by the substantial number of PV module models in the market, each with unique cell technologies. It is, however, established that the front glass type does make a difference in the resiliency of the PV module.
- Glass can be heat-treated as part of the manufacturing process to strengthen it and prevent breakage; glass that undergoes this process will be ~2x stronger than untreated glass and 2mm glass will almost always only be heat-strengthened
- By speeding up the cooling process using forced air to create an even higher surface compression, fully tempered glass is produced, which is ~4x stronger than untreated glass. 3.2mm glass is usually fully tempered but this should always be checked
Considering these factors, there are arguments both for and against monofacial and bifacial PV modules for resiliency. For instance:
- Thicker and full-tempered glass is more common with monofacial PV modules, making them more resistant to mechanical impact damage causing glass breakage than bifacial PV modules where thinner and heat-strengthened glass is used instead
- Bifacial PV modules can better distribute impact stress thanks to its layer symmetry, and removal of the vulnerable back-sheet. In one claim involving a site of co-located monofacial and bifacial PV modules, the bifacial models suffered far less cell damage
The ability of fully tempered glass PV modules to withstand impact from hail is documented. So-called “freezer ball tests” carried out by Kiwa PVEL for hailstones 50mm in diameter resulted in the following breakage rates being recorded [2]:
- 2.0mm heat-strengthened glass: breakage rate of 89%
- 3.2mm fully-tempered glass: breakage rate of 40%
It is anticipated that PV modules with 2-3mm glass will remain steady in dominating market share over the next 10 years, although glass thicknesses less than 2mm are expected to have an increasing market share, approaching 20% by 2034[1]. The cost and weight benefits of these designs are attractive, although concern arises where these may be deployed in areas exposed to hail, particularly those without the awareness of hail from past losses.
The Long-Term Impacts
When a hailstorm passes over a solar PV installation, damaging hailstones can fall within a matter of minutes. And, while not a long-lasting event, the impacts to PV modules are permanent.
Hail often falls within thin lines known as swaths as seen below.
Highly localized hail damage to monocrystalline PV modules, with those in-between exhibiting no visible damage. Very large hailstones in the range of 2.75-4 inches were reported. Included with permission of the asset owner.
Hail damage to rooftop installation in Colorado. PV modules were monocrystalline with tempered glass. Large hailstones in the range of 1.7-2 inches were reported. Published with permission of the asset owner.
In other cases, it can cause substantial damage spanning most, if not all, of the solar PV modules on site.
A severe case of extensive hail damage to monofacial PV modules with tempered glass where the tracker system failed. Very large hailstones in the range of 2.5-three inches were reported. Published with permission of the asset owner.
The immediate to longer term impact of a hail event is a drop in power generation. In a severe event, the utility-scale plant may go offline entirely or operate at substantially reduced power capacity. This is not only due to loss of cracked modules but for safety, as operators may shut down parts of the site including affected inverters and combiner circuits until repairs are made. Therefore, availability can plunge to near zero until repowering is completed.
Clean-up is not a trivial task—numerous inspections will be required, and crews must remove damaged PV modules and debris before repowering can begin, also adding concerns regarding environmental and worker safety.
The logistical challenge of procuring and installing large numbers of PV modules is significant. Delays and cost challenges can arise if the original PV module model is discontinued or if global PV cell or module supply chains are restricted, which is of particular concern to the solar industry in the US, given tariff changes and a reliance on PV module imports—$14billion worth in January to October 2024—partially due to domestic manufacturing unable to keep up with demand[3]. Further repowering works and costs may arise if the pre-existing mounting structure and tracker are not suitable for the available PV modules.
Project owners must also consider the long-term performance hit—even PV modules without glass cracking may have cell damage or experience microcracking. Different cell crack severities are shown below from an example electroluminescence (EL) test:
Cracked cells from a PV module under an electroluminescence test with the following crack types[4]:
- Type A: microcracks (not visible to the naked eye)
- Type B and C: visible cracks
Microcracking
Microcracking may cause damage to PV modules even when there is no visible cracking of the glass and, as such, need to be detected by an EL test. Studies show that panels with hail-induced microcracks can exhibit normal power initially but then degrade faster, with significant power drops appearing years after the event due to degradation after subsequent mechanical and thermal cycling.
[1]. International Technology Roadmap for Photovoltaics (ITRPV) Results 2023 Fifteenth Edition, May 2024 ITRPV-15th-Edition-2024-2.pdf
[2] Kiwa PVEL. Hail Stress Sequence, 2024 www.scorecard.pvel.com/hail-stress-sequence. Accessed July 2024
[3] Share of solar PV modules imports in the U.S. 2024, by country. Published by Ian Tiseo, May 22, 2025. US solar panel imports by country 2024| Statista
[4] Review of photovoltaic module degradation, field inspection techniques and techno-economic assessment - ScienceDirect L. Koester, S. Lindig, A. Louwen, A. Astigarraga, G. Manzolini, D. Moser. Review of photovoltaic module degradation, field inspection techniques and techno-economic assessment, Renewable and Sustainable Energy Reviews, Volume 165, 2022, 112616, ISSN 1364-0321, https://doi.org/10.1016/j.rser.2022.112616.
