Solar panel mounting system

[BAGW]

Hi,

I have a question on solar panels mounting system on metal roof decks. Have anyone had experience with solar panel ballast mount on metal roof deck? Do the solar panels come with the steel framing and is the framing directly mounted on the roof? How is the wind uplift resisted? Will the framing be screwed to the deck?

Do anyone see a problem with attaching the solar panels directly to the roof with no ballast if the deck gets properly insulated?

 

[jayrod12]

A lot of times what I've seen is a racking system where they pop down verticals every 4 or 6 feet, and then run a rail system between these verts. The panels then clip onto the rail system.

 

[VentengInfo]

Usually, the panels are independent of the racking. Solar panels companies don't like to install panels, just sell them. There is no magic formula that will work everywhere. Site location can make huge differences, is the area windy? What's the height of the building, you don't want a panel falling from the 30th floor, a lot of considerations must be verified. Pay special attention in the wind uplift before just thinking that a concrete block will work, calculations are mandatory. If some seller tells you that it works, ask for the wind calculations. Also, the slope of the array will increase the stress on the structure. On the other side, arrays without slope are not very efficient. Ideally, fix the structure and make sure to well insulate the roof penetration. See a picture of the proper seal after leaking issues. The racking contractor doesn't care also if the roof will leak. The insulation must be done by a good roofer. My recommendation is to fix it in a real structure (steel beam or concrete).

 

[Once20036]

I`ve heard a lot of things from a lot of solar installers recently, and I`m not sure I believe any of it. The two best were:
1) "We've done our own wind tunnel testing, and the ASCE uplift values are not applicable. Our tests show approximately zero uplift, therefore, no tension connection is necessary"
2) "the uplift is minimal. It is resisted by "welding" our rubber to the roof membrane. The roof membrane is rated for the uplift resistance, therefore, our system is too"

When we're going these, we don't allow any penetrations in the roof membrane. It just adds points that can leak.
I`m accustomed to seeing them installed on a rack system, as jayrod described. The posts will have a "basket" at the base than can be filled with paver blocks to increase the deadload of the solar array. An average of 6-8psf is what I`m accustomed to seeing.

 

[Dvdt18]

I'm unsure the area you are in, but in our area (Ontario, Canada) the national building code has very helpful structural commentaries for solar arrays on roofs to calculate the wind uplift on the array. Paragraphs 56 to 58 of NBC 2015 Structural Commentaries Part 4 of Devision B.

For part 9 buildings (mostly residential) the racking suppliers in our area have a standardized layout guidelines for the contractors to follow based on our local climatic conditions, roof slopes, wood construction, etc. Anything outside of that they typically prepare a site specific guidelines for the layout and fastening the racking system to the roof with their internal engineers. Similarly for any part 4 building (commercial, industrial, high occupancy etc) a site specific layout and guidelines would be prepared by the racking supplier for the contractor to follow. From there, the site specific EoR would check the structure out to ensure it can support the loads imposed by the solar array.

Other racking suppliers have wind tunnel testing data by various accredited agencies to approve their product and provide more information to the EoR and contractors.

If a ballast system can be used, but the roof cannot support an the dead weight of the ballasts, the contractors tend to connect the system directly to the roof framing members or strengthen the roof to accommodate the system. They tend to not like to connect to a low slope roof due to complications with water entering the roof penetrations.

The Solar America Board for Codes and Standards has some great resources and commentaries for solar arrays as well and can be found here.

http://www.solarabcs.org/about/publications/index.html

You can download their Wind Load Calculation for PV Arrays Report here

http://www.solarabcs.org/about/publications/reports/wind-load/index.html

 

[BAGW]

Thanks all. these are very helpful info