load-bearingroofsolar-panels
I want to install 23 305w panels on my roof. It's a flat roof constructed with 2×8 beams spaced at 24". There is no snow load to consider and we get occasional wind and rain storms a few times per year.
Is this structure sufficient to support a solar array? I can space each panel a few feet apart. Each panel weighs 41lb with a psf of under 2.5.
Installing solar should be one of the last things you do. You should first concentrate on those things that will reduce the amount of energy you will be using. "The Green Building Advisor" has a good article on The Energy Efficiency Pyramid.
I believe this article will help you make some wise decisions about where to start.
Am I missing anything? Is there a piece of equipment I'm overlooking?
Yes. Large solar panels can be bought individually rather than cobbled together from smaller ones. These are designed to feed from the panel as-built rather than having to be modified. Example here.
So what you need to do is find a low voltage garden light system (perhaps one powered by the mains as suggested by @longneck) then replacing its mains voltage converter with a feed from a battery pack charged by the panel. The battery packs could be central or at each light.
Best Answer
2x8’s spanning 14’ can support between 31 psf and 53 psf depending on the species and grade of your 2x8’s.
Your existing flat roof “dead load” (load that does not change) is:
1) roofing between 3 psf and 8 psf depending on the type, number of re-roofs, etc.,
2) roof sheathing is between 1.5 and 2.5 psf,
3) roof joists of 2x8’s is 1.5 psf,
4) attic insulation (if any) is between 2 and 3 psf,
5) ceiling (if any) is between 3 and 4 psf,
6) miscellaneous, including lights, etc. is between 2 and 3 psf
Therefore, the total dead load is between 11.5 and 20.5 psf depending on all the materials on your roof. (Feel free to adjust my estimates depending on your exact materials.)
Generally, we add a “Live Load” (snow load, etc.) to the dead load to get a Total Load. However, you’ve indicated that there is no snow load.
Your 2x8’s spanning 14’ At 24” on center will easily support your solar collectors weighing about 2.5 psf.
So, the 2x8’s will hold them up, but we also worry about holding them down. If you live in a high wind area or seismic area, you’ll need to anchor the collectors to the roof too. Then, we worry about holding the 2x8’s to the bearing walls, then the bearing walls to the footings, etc.
Btw, solar collectors are the perfect shape to fly away...be careful.