Techniques for installing piers with IronRidge ground mount on sloped ground.

[tomski72]

Thank you all for all your thoughts! My first post and first solar install so this forum is fantastic.

I doubt modifying the IronRidge top caps or piers would be OK with my county Inspector. I am getting an engineer involved because I need him to spec an alternate foundation for the 4' deep x 12" diameter hole that IronRidge calls out for my piers. My rocky ground makes that almost impossible, and he says a 2' x 2' x 1' deep footing will work. I will ask him about the lateral loads imposed by going off vertical on the piers and probably use cross braces to hold the assembled array in place before pouring concrete. I also think maybe breaking my 4x6 panel array into 2 smaller arrays of 4x3 panels and "stair stepping" down the east west slope may also solve the problem. Thanks again for the helpful information.

 

[Hedges]

Given a 10 degree slope to the East (West?) and a steep slope to the South, what about rotating orientation so array is facing down the fall line, horizontal is across slope and actually horizontal?

Rocky ground may be impossible to dig with an auger, but can you excavate with a backhoe? 4' isn't much.
If you dig in direction of the row, not in direction array will face, should still have strength of undisturbed soil. Form so concrete doesn't flow to fill trench between uprights. No torsional strength needed in that direction; just backfill.


If you actually had boulders (as large as your planned concrete footings), then I'd suggest core drill to fit your uprights (if single row of poles) or drilled holes for rebar to secure short 12" diameter footings on top.

If that is single row, 2' x 2' would not have same torsion strength as 4' deep by 1' diameter. Also, top 1' of soil would not be as secure as depth. Different material, and subject to erosion.

 

[tomski72]

Thanks Hedges! Sounds like you have seen your share of excavations. Great tips. I'll look into adjusting the array orientation to see if the loses outweigh the ease of install.

 

[CAD]

I have a 5 degree slope and also wanted to have the array match the slope for a 52' wide array.

After searching many places for something better I finally used Iron Ridge hardware.

To get a permit my array needed to be engineered. The engineer that Iron Ridge customer service referred me to, said to use shims at the top caps to deal with the 5 degree slope. But for one the u-bolts were too short for that. Also the Iron Ridge customer service guy said the top caps should be at 90 degrees!

Then after already being paid, the darn engineer stopped responding to me when I asked for options other than the shims.

So I was left with expensive engineering for an unbuildable design. What to do next kept me up at night.

So I submitted the engineer's plans, but then opted to not use the shims. Rather I opted to put a slight 5 degree bend at the top of each vertical so that the top caps could mount at 90 degrees as specified by Iron Ridge. This worked great and fortunately the inspector didn't complain.


While the cement cured and before the rails and panels were mounted it looked like this:



The bend is almost not noticeable unless you look. It allows the verticals to be true plum for optimal weight support. And it allows the downhill side of the array not to be so high in the air, meaning the ballasted foundation blocks didn't need to be as many or as huge as if it was more like a tall masted sailing ship.


(Note, under the tarps are insulated ballasted foundations to protect from freezing as they cured, i.e. huge concrete blocks embedded about 24" deep. A ballasted foundation was used because the ground is hard to dig or bore into here.)


But I had a lot of trouble figuring out how to bend the heavy 3" I.D. mechanical tubing. After calling all over, I couldn't find anyone who could bend these pipes.

In the end, the local welder lent me the old die from an old broken tubing bender he had (orange die in photo below), and I used it with my 27 ton log splitter in vertical mode with a bunch of fancy supports below the tubing including my dad's old anvil to cleanly make the bends without crushing in the front-side or backside from the high force needed for the bends. I got it to bend a test pipe first, then once this worked, launched into bending the actual vertical tubing.

I don't recommend this as it was very labor intensive, but it was the only solution I could come up with.



Note! While bending the free end of the pipe being bent needs to travel upwards! So this pulley and weight system counterbalanced as it was being bent so as not to crush the one underside of near the die.


I drilled all of the brace holes on my garage floor (3/4" bolt holes), then assembled them again after hung. This allowed me to get accurate brace holes with much less trouble.

Also hanging this much weight was tricky and dangerous. You can see the chain hoists to lift the heavy side. The tall leg ended up being set on a dobie (small concrete block used to support rebar) adjusted to make sure the long horizontals were straight.

The short leg was supported with temporary vertical 2x4s during the concrete pour and located N-S with wooden spacers between tall and short legs as seen in the first photo above to hold precise dimensions.






Note, my panel tilt angle is 45 degrees which makes it easy to keep the snow off. Also the short leg is high enough for a fair amount of snow to dump without covering the bottom panels. (Last winter we had a 50 year dump of snow, so I'm glad I allowed this much space for snow, as I expect we might get another 50 year dump once el-nino comes back around.)


And the result is something like this energy graph on a sunny day.