To make purchasing decisions a little more complex for solar panel buyers, there may be a conflict between single and double/double glass panels. So, which is better?
Back in November we checked whether bifacial panels were worthwhile for installation in residential buildings. These panels collect reflected light from the back of the panel as well as direct light from the front. Instead of an opaque backing film, they have a glass back. But not only bifacial modules use double glass, some monofacial modules also use it.
An example is right above my head as I write this. Our 10 kW solar system consists of TrinaSolar 415W Vertex S+ modules. These have 1.6 mm thick glass panels at the front and back. Single glass solar panels typically feature a 3.2mm film on the front and a back made of a polymer material such as PVA.
Advantages of double glass
I have not based our choice of solar panels on whether they are single or double glass panels. However, the latter’s alleged benefits include:
- Although each sheet is thinner, together these provided improved structural strength and reduced the risk or occurrence of microcracks in the cells.
- Increased protection against moisture affecting the solar cells.
- Greater resistance to chemical reactions.
- Less prone to scratches on the backing during installation – and scratches can compromise the integrity of the backsheet.
Disadvantages of double glass
- They may be heavier if the manufacturer used thicker glass (e.g. 2mm). Our 1.6mm front and back panels weigh 21kg, which is comparable to single glass. (But thicker glass can be a very good thing).
- They used to be more expensive – but the price difference has narrowed significantly in recent years. For example, SQ’s solar panel comparison chart shows that 440W Trina Vertex S+ panels retail for around $133 each. This is a cheap chip for a decent quality panel.
- Hail resistance can be a problem.
And with that in mind…
Double glass solar panels and hail
A few years ago, several homes in northern Adelaide were hit by a freak hailstorm. Ours was among the many properties affected. There was tens of thousands of dollars in damage, and after the SES initially provided security (thank goodness), we lived for quite a while with a few large holes in the ceiling of our kitchen and living room covered with plywood .
I would like to say that our panels survived the onslaught unscathed. But we hadn’t installed the solar system yet, which might have been for the best. And if we were particularly prone to large hail, this would have been an important factor in choosing our solar panel.
While our Trina panels meet the basic hail resistance requirements (25mm hailstones are fired at 80km/h – and I’ve read that newer versions exceed this), there is hail and then there is hail. It’s not just the size of the hailstones that matters, but also their speed and direction – and the angle at which the panels are installed (usually the same as the roof).
I don’t know if these panels would withstand the kind of pounding we experienced on this day in 2021. But the damage caused by this event in our case was due to the amount of hail in a very short period of time rather than the size of it. And on stormy days I spend a lot of time staring at BoM’s radar, looking for dark spots; Not that there’s much I can do about it, no matter what happens.
In Kiwa PVEL’s 2024 Scorecard, hail test results showed that 3.2mm fully tempered glass/backsheet solar modules were significantly less susceptible to glass breakage than *2.0mm* heat tempered glass/glass modules.
But even many single-glass solar modules don’t survive particularly strong hailstorms very well. So if your area is prone to large hail and you are considering single or double glazing; Consider placing improved hail resistance at the top of your list of must-have features.
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