Alternative Power sources - Pole Mount Specs

Author

Pole Mount Specs

jeff_s_g@yahoo.com

2006-06-12, 9:21 pm

Hi all,

I am looking to install the footing and pole for a pole mount PV array
and I am looking for some advice. I'll be using a Wattsun AZ-225
hosting 16 Shell SQ175s.

The specs for this include a surface area of 230 sqft with a total load
of ~ 1,400 lbs.

Winds could be as high as 100 mph as a general rule in the region where
I live, however the location of the array is surrounded by large groves
of vine maple and alder (yes, there is very good solar window at this
site). The soil is heavy clay.

Below are som specs, I've come up with:

5'x4'x8' hole

15' 8" Schedule 80 steel pipe where ~ 7' would be in the hole and ~ 8
above ground

5500 psi fiber mesh concrete

2 5/8" holes drilled through the pipe at 2' from the bottom of the
pipe and 2' from the top perpendicular to each other.

Grid of =BD " rebar wired together with 10 - 18" long pieces at the
width and 4 - 5' tall pieces at the height

I spoke with a sign company thinking that they would be able to
recommend a solution. Theirs was a much more shallow hole with no
rebar.

Anyway, looking for comments from those who have expierence or an
opinion. =20

Thanks!

2006-06-12, 10:21 pm

jeff_s_g@yahoo.com wrote:

> 16 Shell SQ175s.

I put up an array of eight 175s the other day on a ground mount. That's
a whole lotta PV...

> 5'x4'x8' hole

I'd suggest, for a single pole, 8x8 x four deep. It's not as big a pad
as you'd think...

> 15' 8" Schedule 80 steel pipe where ~ 7' would be in the hole and ~ 8
> above ground

Yep, I'd go for that, maybe even 12 feet through the pad (eight feet
into the ground below).

> 5500 psi fiber mesh concrete
>
> 2 5/8" holes drilled through the pipe at 2' from the bottom of the
> pipe and 2' from the top perpendicular to each other.

With another pipe through it?

> Grid of =BD " rebar wired together with 10 - 18" long pieces at the
> width and 4 - 5' tall pieces at the height

And I'd do a couple layers of it, say one foot up from the bottom, one
foot down from the top.
For the pole, though, too, I'd make sure it totally passed through the
pad. By several feet if possible, and then it could serve as a
grounding rod, too.

> I spoke with a sign company thinking that they would be able to
> recommend a solution. Theirs was a much more shallow hole with no
> rebar.

Because concrete is expensive, proper rebar takes time, and a sign
falling over won't cost them 15 000$ ;-).

> Anyway, looking for comments from those who have expierence or an
> opinion.

Does it really HAVE to be all 16 on the same pole?
Myself, I'd say you're just asking for it. I'd recommend TWO poles,
with the array between them.

The price of failure, as they say, is quite substantial...

DJ

Jefff

2006-06-12, 10:21 pm

Thanks for the reply, DJ. I can go with a smaller array of 12 quite
fine on a schedule 40 8" pole. Pole is nealy half the price. The
amount of concrete is going to be the same. The hole is already there.
It is hard to get a perfectly sized hole with a backhoe, so I am kind
of stuck with what I have.

Yep, that is a whole mess of panels.

DJ wrote:
> jeff_s_g@yahoo.com wrote:
>
>
> I put up an array of eight 175s the other day on a ground mount. That's
> a whole lotta PV...
>
>
> I'd suggest, for a single pole, 8x8 x four deep. It's not as big a pad
> as you'd think...
>
>
> Yep, I'd go for that, maybe even 12 feet through the pad (eight feet
> into the ground below).
>
>
> With another pipe through it?
>
>
> And I'd do a couple layers of it, say one foot up from the bottom, one
> foot down from the top.
> For the pole, though, too, I'd make sure it totally passed through the
> pad. By several feet if possible, and then it could serve as a
> grounding rod, too.
>
>
> Because concrete is expensive, proper rebar takes time, and a sign
> falling over won't cost them 15 000$ ;-).
>
>
> Does it really HAVE to be all 16 on the same pole?
> Myself, I'd say you're just asking for it. I'd recommend TWO poles,
> with the array between them.
>=20
> The price of failure, as they say, is quite substantial...
>=20
> DJ

nicksanspam@ece.villanova.edu

2006-06-13, 1:21 am

DJ wrote:

> I'd suggest, for a single pole, 8x8 x four deep.

Wow. Isn't there some easier way, like a small thrust pad at the bottom
and 3 or 4 deadmen with stainless steel cables and turnbuckles?

Nick

Duane C. Johnson

2006-06-13, 7:21 am

Hi Jefff;

Jefff <jeff_s_g@yahoo.com> wrote:

> Thanks for the reply, DJ. I can go with a smaller
> array of 12 quite fine on a schedule 40 8" pole.
> Pole is nearly half the price.

Or use a different design that is stronger with
less material. See the tripod designs based on the
Traxle of Poulek and others:
http://www.redrok.com/electron.htm#traxle

The tripod designs place the main stress of the legs
in tension and compression instead of bending moments
as in the "Daisy" mounts.

Yes, there is a bending moment in the main leg but
this is a member supported at both ends which for
a given material is about 4 times as strong.

The total materials costs are much less expensive.

> The amount of concrete is going to be the same.
> The hole is already there.
> It is hard to get a perfectly sized hole with a
> backhoe, so I am kind of stuck with what I have.

And lastly the bases of the 3 legs are widely spaced
so the 3 concrete foundations will consume much less
material. They are designed to support only dead
weight instead of overturning forces.

The standard engineering criteria for wind loads
I use is 10 lbs/ft^2 for a 90 mph wind. Right out
of the national building code. Of course your local
conditions may require a higher loading. Wind loading
is roughly the square of the wind speed.

> Yep, that is a whole mess of panels.

I also suggest multiple tracking mounts for failsafe
reasons.

In addition, the basic bending stresses go up with
the cube of height. So all things being equil:
1. 2 mounts should each have 1/3rd the stress as a
single mount with 2 times the panel area.
2. 3 mounts should each have 1/5th the stress as a
single mount with 3 times the panel area.
3. 4 mounts should each have 1/8th the stress as a
single mount with 4 times the panel area.

> DJ wrote:

Duane

--
Home of the $35 Solar Tracker Receiver
http://www.redrok.com/led3xassm.htm [*]
Powered by \ \ \ //|
Thermonuclear Solar Energy from the Sun / |
Energy (the SUN) \ \ \ / / |
Red Rock Energy \ \ / / |
Duane C. Johnson Designer \ \ / \ / |
1825 Florence St Heliostat,Control,& Mounts |
White Bear Lake, Minnesota === \ / \ |
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Jefff

2006-06-13, 1:21 pm

Thanks Duane. I've seen your site, however it is kind of hard to
navigate, which makes it difficult to figure out what one needs. What
would you recommend for 12 Shell SQ175 panels? Be as detailed as you
wish. If I were to buy these, I need to know all of the pros and cons
as well as sighting issues, etc.

Thanks!

Duane C. Johnson wrote:
> Hi Jefff;
>
> Jefff <jeff_s_g@yahoo.com> wrote:
>
>
> Or use a different design that is stronger with
> less material. See the tripod designs based on the
> Traxle of Poulek and others:
> http://www.redrok.com/electron.htm#traxle
>
> The tripod designs place the main stress of the legs
> in tension and compression instead of bending moments
> as in the "Daisy" mounts.
>
> Yes, there is a bending moment in the main leg but
> this is a member supported at both ends which for
> a given material is about 4 times as strong.
>
> The total materials costs are much less expensive.
>
>
> And lastly the bases of the 3 legs are widely spaced
> so the 3 concrete foundations will consume much less
> material. They are designed to support only dead
> weight instead of overturning forces.
>
> The standard engineering criteria for wind loads
> I use is 10 lbs/ft^2 for a 90 mph wind. Right out
> of the national building code. Of course your local
> conditions may require a higher loading. Wind loading
> is roughly the square of the wind speed.
>
>
> I also suggest multiple tracking mounts for failsafe
> reasons.
>
> In addition, the basic bending stresses go up with
> the cube of height. So all things being equil:
> 1. 2 mounts should each have 1/3rd the stress as a
> single mount with 2 times the panel area.
> 2. 3 mounts should each have 1/5th the stress as a
> single mount with 3 times the panel area.
> 3. 4 mounts should each have 1/8th the stress as a
> single mount with 4 times the panel area.
>
>
> Duane
>
> --
> Home of the $35 Solar Tracker Receiver
> http://www.redrok.com/led3xassm.htm [*]
> Powered by \ \ \ //|
> Thermonuclear Solar Energy from the Sun / |
> Energy (the SUN) \ \ \ / / |
> Red Rock Energy \ \ / / |
> Duane C. Johnson Designer \ \ / \ / |
> 1825 Florence St Heliostat,Control,& Mounts |
> White Bear Lake, Minnesota === \ / \ |
> USA 55110-3364 === \ |
> (651)426-4766 use Courier New Font \ |
> redrok@redrok.com (my email: address) \ |
> http://www.redrok.com (Web site) ===

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