Why are solar panels encased in glass instead of tougher materials?
bluesolar
| Posted in Energy Efficiency and Durability on
Hi all — Why do PV solar panels use glass instead of tougher materials like polycarbonate?
I realize that solar panels tend to be fairly tough, but wouldn’t they be even tougher if they weren’t made of glass? (I mean the exterior encasement.)
Bonus question: Why do solar panels have glass backs? That really stumps me. I first learned of this when I watched this First Solar video outlining how their new Series 6 panels are made. I’m not sure if this is true of all panels or just some: https://vimeo.com/245803424
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Replies
I don’t have a definitive answer, but my guess is that glass is cheaper than polycarbonate and (although more fragile) doesn’t scratch as easy. Also, glass can probably handle extended UV better than polycarbonate and perhaps snow slides off glass easier.
Glass also has a low rate of expansion/contraction across wide temperatures, which may explain why the bottoms are also glass (consistent with top). construction would be simpler ave cheaper with lower envelope expansion rates.
Glass is also very dimensionally staple, while polycarbonate may be more prone to warp over time in this type of application.
Glass is impervious to ultraviolet light, the high temperatures you get in full sun, and is very stiff which helps to protect the solar cells inside. Polycarbonate will haze in ten years or less in most cases, and it’s relatively flexible which means bending of the panel risks damaging the solar cells inside.
There is a nasty tradeoff in materials: harder means more brittle, tougher means more malleable (flexible). Since the solar cells themselves are made primarily of silicon, they have properties very similar to that raw element: stuff and relatively brittle. Glass is also stiff, so much thicker (compared to the solar cells themselves) glass panels provide good protection to the silicon material the solar cells are made of.
Glass is actually a pretty durable material. Remember that many things are “fiberglass reinforced”. I can tell you from experience that the 125 micron diameter glass strands in fiber optic cables are VERY strong compared to their size. It is nearly impossible to break one by stretching it with your hands.
Bill
You can get solar cells embedded in flexible material, plastic backed with some sort of clear epoxy holding the hole thing together.
These panels are more expensive, scratch easily, and will probably cloud from extended UV exposure. I’ve used them in applications where a glass panel would get smashed and for that they are worth it, but otherwise I’d go with glass.
These flexible panels also have much lower energy density in terms of watts per square centimeter compared to the crystalline silicon (rigid) solar cells.
Bill