[RE-wrenches] Tall pole mount

[R Ray Walters]

I designed a pole mount for the US Forest Service that was 20 ft out of the ground. Its basically telescoping sections of pipe, welded together. The base was 8" Sch 80 for 10 ft, then 6" diam, and finished the last 6 ft in 4" diam.
We used a massive footing with lots of rebar that was 8 ft below the ground, and spread out quite a bit. The torque calculations are not that hard to do, but its amazing how much ballast you need as the torque increases with height. (we used the inverted mushroom shape, and then made use of earth ballast on top of the concrete.)
I would recommend a base plate that bolts to J bolts in the concrete, as setting the pole in concrete, and securing it level while the concrete drys is a PIA.  Getting a used (pre engineered) large sign post would be your most cost effective solution, I would guess, and they probably would have a standard design for the footing for your particular soil conditions.
Then you just match the array sq ft to the sign's sq. ft.
An engineer would save you money possibly, as its easy to over kill this design, and blow the budget. You want it specifically for your soil type, and your local code requirements for wind speed.

Another option I've tried is just a straight 6" pole, with guy wires and screw in earth anchors (or set in concrete if your soil type requires it). This doesn't require near the foundation, but you have to deal with guy cables similar to a wind install.
Not as pretty, but perfectly acceptable from an engineering stand point.
I can send you some pics of both if you like.
I've considered the timber lattice structure as well, I think its better for larger arrays that won't fit on a single pole (over 2000watts?)

BTW, Most of the times that I've run into this, we just went with a roof mount.

R. Walters
ray at solarray.com
Solar Engineer




On Mar 22, 2011, at 7:13 AM, <holtek at sbcglobal.net> wrote:

> Situation:  Client has limited locations for array due to trees. There is one spot that would work IF pole mount is 20-25' (that would put the array top edge at 30'+). Will need to incorporate tracker to maximize production. Will definitely be consulting structural engineer.
>  
> Questions: Anyone tried this? Comments or lessons learned?
>  
> Holt E. Kelly
> Holtek Fireplace & Solar Products
> 500 Jewell Dr.
> Waco TX. 76712
> 254-751-9111
> www.holteksolar.com
>  
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