· 5 min read · By Hotsolar engineering team
A heavy hailstorm hits, you hear the ice hammering the roof, and your first thought is the solar panels. The short answer is that normal hail won't break them. Every model sold in Europe has passed a test where ice balls are fired at it at more than 80 km/h. Very large hailstones can cause damage, and for that case it's worth checking your home insurance.
What the front of a solar panel is made of
The side of the panel you see is tempered glass, usually 3.2 mm thick. Tempering is a heat treatment that makes glass several times more impact-resistant than window glass, like an oven door or a shower screen. The cells sit underneath, encapsulated and bonded to that glass, and an aluminium frame holds everything together.
Some glass-glass modules (bifacial ones, for example) use two thinner sheets of about 2 mm each. They handle normal use well, but against large hail 3.2 mm glass holds up much better, as you'll see below.
The hail test every panel has to pass
To sell a module in Europe, the manufacturer has to certify it to the IEC 61215 standard. One of its tests, MQT 17, is the hail test:
- Ice balls 25 mm in diameter are made and kept in a freezer.
- An air cannon fires them at the panel at 23 m/s, about 83 km/h.
- There are 11 impacts, each on a specific spot: corners, edges and areas near the frame, where the glass is weakest.
- Afterwards the panel is checked for major visible defects and to make sure it still insulates properly, including when wet.
If it fails, the model doesn't get certified. So a panel with IEC 61215 certification has already taken eleven hits from 2.5 cm hail without breaking.
| Hail | Rough size | What usually happens |
|---|---|---|
| Up to 2.5 cm | chickpea, marble | What the test simulates. No damage to a certified panel. |
| 2.5 to 4 cm | walnut | Above the test. A panel with 3.2 mm glass usually withstands it. |
| Over 4 to 5 cm | golf ball or larger | Can break the glass or leave microcracks in the cells. |
Rough guide. What each panel withstands depends on the model, the glass and where the hailstone hits.
When it can break
Hail the size of a golf ball (about 4.3 cm) or larger can cause damage. In the module scorecard published by PVEL, an independent lab, panels were tested with 45 mm ice balls: about 97 % of panels with 2 mm glass failed, compared with 13 % of those with 3.2 mm glass.
Some manufacturers test their panels with balls larger than the standard requires, 35 or 45 mm. If you live somewhere with strong hailstorms, it's worth checking the datasheet.
With large hail the damage isn't always visible. The glass can stay intact while microcracks appear in the cells, which over time make the panel produce less.
What to do after a heavy hailstorm
- Check the inverter app over the following days and compare production with similar sunny days before the storm. A clear drop is the first clue.
- From the ground or a window, look for any glass with cracks or a spider-web pattern.
- Don't climb onto the roof to check them, especially if it's wet. If something looks wrong, call an installer.
- If there's damage, take photos and tell your insurer as soon as possible.
Does home insurance cover it?
Panels fixed to the roof are usually treated as part of the building (the "continente" in Spanish policies), so home insurance normally covers them like the rest of the house. Two things are worth checking in your policy: that it includes damage from hail and weather events, and that the panels are declared. If you added them after taking out the policy, tell your insurer so they're included.
Every policy has its own conditions and limits, so what yours says is what counts.
Frequently asked questions
Does normal hail break solar panels? No. Panels certified to IEC 61215 withstand 25 mm ice balls at about 83 km/h, which is more than a normal hailstorm brings.
From what size can hail damage them? Hail over 4 or 5 cm, golf-ball size or larger, can break the glass or cause microcracks. It's uncommon, but it happens.
How do I know if my panels are damaged? Production is the most reliable sign. If after the storm the inverter app shows clearly less on similar sunny days, have them checked.
Which panel handles hail best? One with tempered glass of 3.2 mm or more and, if possible, tested with larger balls than the standard requires. It's on the datasheet.
Worried about hail on your roof?
If you're thinking about getting panels, we'll help you choose modules with glass that holds up and show you what to look for on the datasheet. If you already have them and they produce less after a storm, tell us and we'll look at what might be going on. More on our homes page, or message us on WhatsApp with the word PANELS.
