Re: Solar panel mounting with VHB tape
AM Solar sells brackets wherein you mount the foot, and then another piece mounts to the panel. The panel piece has a captive nut, and a thumbscrew goes through the foot and into it. Each foot has 2.5 square inches of VHB surface area, and as far as I know they haven't had any fly off. The arrangement allows for tilting up the panels for better sun angle, or just to wire them up, clean under them, or etc.
Still, I wanted a bit more VHB surface area (I mean, why not? I couldn't see any downside.) I also didn't want to worry about the galling of stainless to stainless (fastener to captive nut). And too, the pre-made holes in the AM Solar feet weren't at quite the right place for my install. So, I made up my own mounting pieces. Caveat is that I have not mounted them yet, however I did help a friend mount three panels to my former SMB (he owns it now) and we used similar pieces. He reports that all is well.
What I went with is some 2" x 2" aluminum angle (3/16" thick - although I think 1/8" would have been fine). Each foot piece cut from this is 3" long, thus each "foot" has 6 square inches of VHB area. So a panel has 24 square inches (vs. 10 square inches on the AM Solar mounts, which reportedly work just fine). Then I made a "knuckle" piece that attaches to the bottom lip of the panel and hangs down - those are 1" x 1"x 1/8" angle. The theoretical plan is to put a rivnut in the knuckle and then use a shoulder bolt through the foot and into the rivnut. Another version of a captive nut.
My idea is fairly similar to the "sticky feet" pictured above in function, but with slightly different details.
I was originally going to put the rivnut in the "side wall" of the solar panel, but upon close inspection I found that must be a "hollow" wall (because while the aluminum is around 1/16" thick, the wall is more like 1/4" thick. Hence deciding to go with a "knuckle" attached to the bottom horizontal lip (which is solid). I originally wanted to go with the sidewall rivnut to get the panels closer to the roof for sleekness factor, but then I did an experiment with the panels up on the roof and decided that might heat up my roof too much. With the knuckle the panels will be around 1" to 1-1/4" off the roof.
When we did my buddy's SMB, he made the feet out of 2" x 3" angle, with the 3" side on the roof - so even more area for VHB. That said, in a couple of of spots the whole 3" part didn't contact the roof fully, due to the PH not being perfectly flat. It was still very close (he filled in with a little bit of caulk in a couple of spots), but I think 2" angle will be a good balance of the factors (at least I hope so!).
Another plus to using a separate foot and panel bracket is that you can accommodate a rounded or slanted roof (I mean, you can have the angle of the panel independent of roof angle, if you want to, but placing the locations of the holes).
I didn't like the idea of having the panels basically permanently VHB'd to the roof (as in the case of Z-brackets), so that's why one or another two piece design appealed to me (same thing as you are noticing).
Like I say though, I haven't actually mounted mine yet, so the jury's out on how well it will all work in reality.