Photovoltaic Array Support

[RHTPE]

Hi folks,

I'm back with another interesting design challenge. This time it's a monopole PV array support that I've been asked to evaluate. I seek your thoughts on the following:

1. Should a ground-mounted PV support structure be designed for the same loads as the building it serves (i.e. ASCE 7)?

2. Has anyone in the US had experience with a local building official who actually questioned the design of the supporting structure? Did they require a design sealed by a P.E.?

The designer & fabricator of the PV array and its support are experiencing heartburn over what I've come up with. Their concern is that the competition is not building anything anywhere near as stout. Code required wind speed is 100 mph, exposure B. The initial pole was 8" schedule 40 pipe - we are now using HSS 12" diameter, 1/2" wall, primarily to deal with wind forces.

I am waiting for a letter from my State Building inspector to confirm my belief that the code mandated loads should be used. Yet, as a construction engineer, I feel my client's pain about his competition. I have suggested that he have a colleague contact the competition to see if they can provide a drawing for the building inspector that has been stamped by a P.E. If they can, I'd love to learn what the support has been designed for.

I'm sure you all have opinions, and I'd loved to hear what you all have to say.


Ralph
Structures Consulting
Northeast USA

 

[IRstuff]

This link is related to another thread about solar panel mounting: thread626-261703

http://www.unirac.com/mounting-solutions/unirac-large-array.php?solution=roof-mount

They claim "Capable of withstanding Zone 4 seismic events or extreme wind or snow loads"

TTFN

FAQ731-376

 

[JAE]

This is used for pole/light fixtures as well...might check it out:

https://bookstore.transportation.org/item_details.aspx?ID=1319

 

[RHTPE]

IRstuff - Thanks for the links. None really address the issue of proper design of the supporting structure though. Unirac seems to max out at 100 square feet of array on a single pole - my client is installing 475 square feet on a single pole.

JAE - Probably a very helpful publication, and one to put on my shopping list for that point in time when my billings far exceed my usual monthly expenses.

But what I'm really curious about is the building official attitude about the installation of these supports. Do they insist on an engineer signing off on the installation, or do they simply take the hardware manufacturer's cut sheet and accept that as adequate? Unirac has an interesting comment on all of their cut sheets:

"The installer is solely responsible for: complying with all applicable building codes, including any that supercede these instructions; pole installation appropriate for local wind and soil conditions; ..."

This effectively shifts the responsibility off their shoulders and onto some one else's.


Ralph
Structures Consulting
Northeast USA

 

[dcarr82775]

IMO the simple answer is yes, the foundation/support needs to be designed to code loadings.

I think it depends on the size of the equipment. The large wind turbines in CO have foundations designed by PE's, but I would be surprised if many of the smaller pieces of equipment have an engineered foundation/supporting structure. The loadings in ASCE7 for non building structures apply. In the past I have found that the Canadian Code is better equipped to handle odd individual shapes than ASCE7 so I take a few liberties and combine bits and pieces of each code in a manner that makes sense to me.

 

[fcuneo]

Hi Ralph,

With stricter regulations, most PV manufacturers rather have a PE sign off the design and avoid major problems.

I think we might be able to help you out. We have a vast experience providing wind-loading assesments on solar pannels.

Feel free to contact me,

Fernando Cuneo


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Newmerical Technologies International
Montreal, QC, Canada
Tel: +1 (514) 398-2671
Web:

http://www.cwe.newmerical.com