The panels them selves are not very heavy. The problem of getting up there to install might prove to be the issue. Also, if you decide to go ahead with installing them, I would suggest you make sure
you anchor them to the rafters, not just to the roof.
They also have the stick on panels. I'm not familiar with those and not sure just how well they have worked out for people. I have heard it said that laying tight up against the roof, they can't get rid of the the heat. That's where the traditional panel has the advantage being up off the roof with a mounting bracket.
Good luck with it if you proceed.