I didn't want to screw them directly into the roof (worried about causing a leak). I ended up tying them down with thick rope, the rope is pinned to the back with an alumnium bracket which is screwed into the side of the wood roof. They are plenty sturdy so that they wont budge during heavy winds which is all I worried about.
Last year before I tied them down, I woke up on a VERY windy night and found them inches away from getting blown off the roof... couldn't believe it!
http://i269.photobucket.com/albums/jj62/dnix71/solar31.jpg
You can see the tape on the second from the right.[ Parent ]