Wind-Loading and Tilted panels on roofs [RE-wrenches]

[Ray Walters]

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   we need to mount some modules to a roof that has an East/West 
orientation (ie the ridge line runs N-S)....so that to face our modules 
south we would have to mount them on either the east or west roof space 
tilted to the south. Unfortunately this is the only good solar access on 
the property...but we have concerns about the wind-loading.
>
>Any comments?
>
>Thanks!
>-Justine Sanchez
>Solar Energy International
>
Hi Justin;

We deal with odd angles like that by using a pole mounted array close to 
the roof, but not attached at all. The pole runs down the north wall sits 
in concrete and is attached to the facia or rafter tails with unistrut and 
the proper sized pipe clamp. Usually 5 to 6 ft of pole past the roof edge 
is enough to still get a decent winter tilt on the array and leave a foot 
or so clearance between the bottom modules and the roof. The Trig can get 
pretty involved, but as they say "its not rocket science".
I prefer this method for many reasons:
1) NO roof penetrations or liability for leaks.
2) Looks cleaner than odd angled stuff on the roof.
3) Easy tilt adjustment, and even some degree of azimuth adjustment possible.
4)  You have a combination of mounts that work together, pole set in 
ground, attachment to rafter ends, and even could add an additional bracing 
to the wall midway.
5) No DCGFI required, since you are NOT actually attaching modules to the roof.
The down side of this method is that you often are confronted with very 
tall pole (18 ft for a single story with 4:12 pitch), so you may need a 
crane or backhoe, etc. to handle it.
We slide the pole off the top of our truck roof rack, and let one end down 
into the hole. Then we secure the high side of the pole to an extension on 
our roof rack, and slowly back up till the pole is near vertical. At this 
point, we loosen the bindings enough to get a few degrees of tilt, so that 
we can set the pole plumb, then we secure it to the Unistrut with the 
clamp, and pour the concrete around the base. This method works for 6" 
poles up to 24 ft, taller or larger diameter than that, and you would 
definitely want a crane.





Ray Walters
ray at solarray.com
President, SolarRay, Inc.
NABCEP Certified Solar PV Installer
BS Mechanical Engineering, UT Austin 88
Returned US Peace Corps Volunteer 

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