In a fight between a fierce hail storm and a bunch of solar panels, who would win? | Image: Google Maps
A National Renewable Energy Laboratory (NREL) facility in Golden, Colorado was witness to an unscheduled test provided by Mother Nature of large hailstones pummeling its solar panels.
According to the Denver Post, a hailstorm earlier this week caused chaos across the area and wreaked a massive amount of damage. Hailstones up to 7cm in diameter smashed into cars, infrastructure and people.
Apparently the onslaught from the heavens may prove to be among the most costly hailstorms to ever hit the Denver area.
The region is home to the NREL’s Golden, Colorado Laboratories and Offices; which also experienced similar-sized hailstones. CBS Local reports that while many vehicles belonging to NREL employees were damaged, the facility’s solar power system fared pretty well.
Only one module out of the 3,168 solar panels on NREL’s Research Support Facility sustained damage.
Solar panels need to be able to withstand 25mm diameter hailstones weighing 7.53 grams traveling at a velocity 23 metres per second (82.8 kilometres per hour) per international standards (IEC61215). Particularly good quality modules in this regard will withstand larger hail traveling at a faster speed.*
“The test equipment is a unique launcher capable of propelling various weights of ice balls at the specified velocities so as to hit the module at 11 specified impact locations +/- 10mm distance variation. The time between the removal of the ice ball from the cold storage container and impact on the module shall not exceed 60s.”
The following video shows a “quick and dirty” experiment using a high-pressure pneumatic cannon loaded with ice, plastic and metal balls.
The resilience of solar panels to hail is largely due to high quality tempered glass, usually around 3 – 4mm thick. Even if damage occurs, the glass doesn’t shatter into sharp shards, but breaks into smaller pieces that retain form. As with any component, the quality of tempered glass used in various brands of solar panels can vary.
It’s reassuring that good quality modules can survive much of what nature may potentially throw at them. However, if you live in an area particularly prone to nasty hail storms, it’s a worthwhile exercise as part of your due diligence when choosing a solar power system to look into what size hailstones the panels can withstand.
“Hail testing is mandatory under Australian and international PV standards. IEC 61215 and IEC 61645 for crystalline and thin film modules respectively require modules to survive 25mm diameter ice balls fired at 23m/s on 11 points across the module for the Moderate Hail Test (Class MH) or 75mm under the Severe Hail Damage Resistance Test (Class SH) (TUV Rheinland 2009).
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There have been various articles and studies predicting increasing hail size with climate change, although there is no certainty. For example this article and the comments which follow it: https://theconversation.com/australia-faces-a-stormier-future-thanks-to-climate-change-35327
Even now, hail can occur in sizes much greater than that being tested on panels. For example, John Allen from Columbia University states that “The Sydney basin regularly sees size is greater than 7.5cm (the Melbourne hailstorm in 2010 produced 10cm hail, and other Victorian storms have reliably produce stones to 15cm). The largest documented hailstones in Australia have been between 15-20cm in present climate, even though the length of record is short. Recent research in the United States has revealed that 15cm+ hail is probably less uncommon that we think (state and national records have been broken several times in recent years), and often encountered with the strong updrafts associated with supercells.”
Also from John Allen: “Typically a 3cm hailstone will be enough to minor dent vehicles, 4.5cm will start to damage windows, pierce plastic roofing and do larger dents and may kill birds, 6-7.5cm will begin to do damage to tile roofs, will shatter windows and go through car side windows. At 10cm, stones do major damage to vehicle surfaces, will go straight through windows/windshield and do serious roof damage to homes. Once we get into the 15cm plus range, roofs will be pierced unless they are metal (and even then some will), and the stones are likely to kill on impact.”
While I welcome Michael Bloch’s contribution, I’d like to see how those of us in very hail prone areas CAN find out which panels are better for hail.
Michael says: “Particularly good quality modules will withstand larger hail traveling at a faster speed.” and “it’s a worthwhile exercise as part of your due diligence when choosing a solar power system to look into what size hailstones the panels can withstand.”
Yet following the links in Michael’s article do not seem to reveal any information that helps the panel buyer find the better panels, and in my experience asking installers is a waste of time, with a brush off like: “yeah I’ve been in business for X years (generally 5-7) and it does not happen” when clearly it does sometimes, somewhere in Australia, just not yet where he works. More facts about panels, hail size, actual storm results and panel testing would be welcome as well as anecdotes, superficial videos and opinions.
There is some data available, though not on specific brands. In this 2012 study, 3 out of 5 rigid panels were intact after 1″ and 1.5″ simulated hail, but failed with 2″ hail. http://rci-online.org/wp-content/uploads/2012-CTS-koontz.pdf
This study from Intersolar 2015 shows a difference in crack frequency with simulated 25mm, 35mm, 45mm, 50mm hail between solar panels which have 3.2mm and 4.0mm glass, although the frame type seems to also be relevant. http://iea-pvps.org/fileadmin/dam/public/report/technical/03_Intersolar_2015_TASK13_Hail_Mathiak_ohne_-_2.pdf
Thanks Greg for the interesting information. Apologies for the slow response.
My take aways are:
One possible reason why we do not see more hail damage is because ice ball testing perpendicular to the panel does not replicate the structure of real hail which is layered so may have different characteristics as the ice ‘explodes’ on impact.
The testing outlined seems to be an engineering or physics based response based on assumptions, not a scientific one based on observations of real life followed by hypothesis testing.
Hail in reality comes from widely varying angles, and it has varying shape, mass density, structure, velocity and durations For example, in real life would panels deform differently when struck concurrently or quick succession by multiple hail stones rather than one single one? Would actual hail with a layered and non-uniform structure, as it deforms and explodes, transmit different forces (perhaps greater, perhaps lower) over a different number of milliseconds compared to a comparable mass uniform ice ball?
As well, in real life panels have widely varying structures not only in glass thickness and type, but also in panel structure. For instance the latest LG panels can take twice the force on the face side as say Canadian Solar which is around the average for all panels, but who knows if this figure relates to snow, wind or hail or a combination? Perhaps some examples of stronger panels could be less able to absorb forces through deflection of the glass?
As shown in your links, ice balls (and presumably hail) if they increase in diameter by 60% which is not much, can impose an increase in force of 300%, so imagine the huge force of the really large hail.
Finally, as quoted in one of your articles: “Damage to some of the PV panels was very subtle and not easy to see. Following a hail event, a user may want to monitor the PV system, comparing performance before and after a hail event to deter- mine if there has been any substantial drop in electrical output.”
This could mean that more damage is happening than gets reported because installers are only called out when there is damage visible from the ground, and most current systems cannot show small faults at panel level.
I guess we have to wait until a huge hail event which insurers fail to cover because it was outside the tested ability of the panels, to find out what the future holds. In the mean time anecdotes prevail.
Great article. Berowra has just had one of those once in a hundred years (small exaggeration as they happen more frequently) hail storms. Many solar panels were horribly damaged. Might be time for an update. There will be many damaged panels that insurance companies are removing for you to investigate.
Ditto to the Berowra Hail storm …. Most Solar panels in Berowra Heights were destroyed, I have 23 panels and all were destroyed. Over half were smashed to pieces and the rest had cracks. Several were not only smashed but pulverised down into a bowl shape up to 5 cm deep in the middle. They look like they have been taken to with a sledge hammer. The hail looks like it came down in clusters as many have multiple hard impacts damage ten next to those there is one or two with micro cracks and then more smashed to pieces. I have an evacuated solar tube hot water system as well. 25 of the 30 tube were smashed to pieces about the size of a 20 cent piece. Also my Colourbond roof which was only 2 years old and installed with the heavier gauge steel (.48 BMT instead of the usual .42 BMT to meet bushfire regulation) was also destroyed. The tops of the corrugations dented down 2cms in place over the entire roof, carport, garage and shed. The hail was a mix of perfectly round hail the same size as a tennis ball and slightly larger hail (6 to 7 cm) with jagged edges sticking out All about around $60Ks damage. Fortunately the Colourbond roof although destroyed saved the day and kept us water tight as many houses with tile roofs were destroyed inside with sever water damage and collapsed ceilings. The hail also puts a dent in the ROI calculations!