In this answer Russel says solar panels are:
a sandwich of glass + bonder + silicon PV cells + bonder + backsheet
This got me wondering how much of those materials are needed to make the solar cells easy to transport and/or install. Assuming (for the sake of this question) that I invent a robot that will 3D-print solar cells directly on to my roof, how could such a machine work, and would it still need all those layers?
EDIT: to clarify, the main thrust of my question is: isn't the backsheet (and its bonder) just needed for ease of transportation? And isn't the glass needed for protection? (e.g. so if I am putting silicon PV cells directly on the roof, and not needing to transport/install big panels, can this glass be much, much thinner, or even done away with completely, and some simple waterproof spray used instead?). I.e. do the backsheet and glass layers do anything beyond make the panels easier to transport and install?
In addition, and especially as this is the Sustainable Living site, how might their overall energy cost compare? E.g. we have solar cars, so a robot crawling over my roof using only solar-power seems reasonable. Assume I have a good source of sand within 1km. Can I just pour sand in to get the silicon, or is making silicon from sand in your own back-yard not reasonable, and is always going to require a big facility?
P.S. I'm not asking how to do the above today. I'm wondering with say 5-20 years of direct R&D effort, what kind of product might be possible. (And I'm thinking not just roofs, but also robots that paint solar panels on top of deserts, or over radioactive areas of Fukushima, etc.)