Tempered glass is made from regular glass, but once it's heat treated you can't cut it.
You might find tempered glass already framed. You would have to make your solar panels to fit. We used to sell motivational lithos framed in tempered glass. It was made in large quantities to match the frame/litho. We threw away a dumpster load after too many got broken shipping. We use polycarbonate now.
http://www.amazon.com/gp/product/B000EZMHEI
If you shop WallyWorld or Target, they sell "pyrex" glass cutting boards for $10 and up.
Those are tempered glass and reasonably clear. Make your solar panel that size and frame it.
http://www.hollidaypictureframes.com/products/Glossblackmetalframe.phtml
Will cut to your specified size. The frames we buy for lithos assemble easily with a flat-tip screwdriver.