A bit of an update:
I just spoke with someone at a glass sealing place. He reluctantly admitted that they would be able to do a custom sealing job, though he repeated many times that there would be no warranty - hey, no big deal; this was a homebrew project from the start, so I never expected any warranty.
He mentioned problems with tempered glass, such as heat buildup problems. He said that he has customers reporting exploding windows in springtime, as there are extreme temperature fluctuations sometimes - freezing at night, to 60-70F daytime. That, with the solar panels inside heating up the sealed environment - even thick tempered glass would explode. He suggested polycarbonate then, and said that it is a lot more durable, but also more expensive.
I'm wondering seriously about this other idea (and jimjjnn suggested something along these lines):
1/8" Aluminum 5052 sheet as a backing, reinforced by a few crossbeams if needed, which can also act as a heatsink, and polycarbonate in front, raised above the solar cells by maybe a quarter or half inch. This could be sealed - the aluminum should be able to sink some heat away, and the polycarbonate might be able to flex enough to allow for thermal expansion and contraction. Plus, the PC is treated for UV light, so, while it'll reduce some light transmission, it'll also not deteriorate over time.
Hopefully the seal will also keep water out - can't go and have condensation in there.
I just don't know where to get all of this material cheaply; if the costs keep going up like this, I might as well just buy ready-made panels! I don't want to make the panels so cheap that they just blow up in 2 years.
