This is a prototype on my shed before I make actual project with 20 panels, which will use pressure treated rails and oak brackets, sealed and stained.
80" 2x4 rail sits on 1" spacer (and silicone caulk mess) to allow water flow, held by 2 large deck screw. There are 3 spacers in this prototype, but only 2 have screws that connect to rafters. There will be 2 rails per solar panel pair, top and bottom. Each bracket is held by 2 smaller deck screws.
Actual project will sit on metal roof with 20deg slope (4/12). It has 1.25" high ribs so I will not use spacers there.
Mounted brackets form 0.75" deep slots to slide panels frame in (picture 2 and 3). Once they are in, they will be secured on the bottom rail with single screw to prevent up and down movement.
Panels are 41lbs each and they will be mounted in pairs like here. I have 250lbs and stepped on this rail, did not bend, tried to shake and rip it out, whole shed was shaking instead. I think even 2x2 could be enough for the given load.
Looking for some idea about ice buildup under rail and snow loads, not particularly worried about wood, but screws. Do I need to use structural screws or deck screws will be fine? I am told that panels wont hold much snow, it will slide off. There will be about 1ft of the roof ridge above panels, so IMO there should not be enough snow load to shear strip the screws. I have lost electrical mast to the snow on this same roof last spring, but nobody was there to heat the house up, so it was whole winter snow buildup of the whole 13' roof slide. This wood mount is not meant to last 25yrs but 10 would be nice.
Why would you bother making wood racks for solar panels when purpose-made aluminum racks are readily available?
20 panels is a very large array. I have 6 at my off grid cottage which run everything including my electric fridge from April - November with no issues. What are you powering?
This installation is going to attract a lot of attention and you will get a visit from the ESA and your local building inspector. You need a building permit to put panels on a roof and you need permits/inspections for the electrical work.
Your home made wood racking is not likely to pass any inspections, could be considered a fire hazard etc. And current codes typically do require a barrier around the panels to prevent critters from nesting under them and also a disconnect for the array that the fire department can easily access.
