Ground mount helical pile specifications

[unhandled]

I’m looking at helical piles for a ground mount installation in Canada and I’m a newbie to solar installs to start with.

I had a poor experience with sonotube install for my fence, probably a poor job from the installer.

The helical pile manufacturer asked for for the specs as to what would be necessary but I’m not sure how to figure that out. I can probably figure out compression specs by calculating panel + racking weight. For the rest, not sure.

I was thinking of having 2 separate sections of 3x4 panels in landscape maybe 3’-4’ feet off the ground to clear snow accumulation while also to minimizing wind effects.

Has anyone went through a similar install and could provide guidance?

Thanks!

 

[Mike 134]

Several racking manufactures have design programs for ground mounts. You might find your answer there.

 

[OzSolar]

The helical pile manufacturer asked for for the specs as to what would be necessary but I’m not sure how to figure that out. I can probably figure out compression specs by calculating panel + racking weight. For the rest, not sure.

You have lift, shear and vertical loads on the piers. Lot more going on there then one might think.

In a perfect world you'd get an civil/structural engineer to calculate and design the appropriate anchoring. They will need a soils (geotech) report to do that.

Are you going to have pull a permit for this project?

 

[MarkSolar]

You can get helical piles from a lot of solar places, I got my ground screws from Sunmodo, they have helicals too. Ironridge carries ground screws, not sure about helical piles. Buy from some place that will give you the engineering drawings with the equipment, you won't have to get involved in doing any calculations.

Why do you want piles instead of ground screws? Helical piles are almost impossible to drive into rocky soil, they're really only good for sandy/soft soil or with high water tables. You also have the option of pouring a floating concrete slab and attaching it to the slab. Then you don't have to dig holes and you don't need any specialized equipment.

 

[unhandled]

Why do you want piles instead of ground screws?

Good question! After looking more into ground screws, I don’t think that would be well suited to Quebec’s climate. Helical piles go well under the frost line vs ground screws seem to not go deep enough. That’s probably why the installers around here all install helical piles.

 

[SparkyJJO]

I have ground screws (small ones) for my fence and they're working there so far through a couple winters, but I've wondered about frost heave over time. Definitely wouldn't want them for something that needs to remain perfectly in place.

There are larger ground screws that very well may go below the frost line. I'm not sure.

 

[MarkSolar]

Good question! After looking more into ground screws, I don’t think that would be well suited to Quebec’s climate. Helical piles go well under the frost line vs ground screws seem to not go deep enough. That’s probably why the installers around here all install helical piles.

Ground screws and helicals are both required to have the threaded/helical part below the frost line so they can't heave. Around here the frost line is 40", my ground screws are 7' and they extend above the ground about 6", so that puts the threaded portion entirely below the frost line. Helicals and screws make the same design assumption: the soil that feezes to the top part of the shaft and tries to heave it is resisted by the force of the helical/screw holding it down below the frost line. I think as long as you choose a device that's long enough it won't matter from a heaving standpoint which device you use.

 

[SparkyJJO]

The sides of the piles/screws at the frost line are also relatively smooth so not as much for frost and ice to lift on.

 

[harjms]

One system I've been considering instead of ground screws is a system by Osprey. One of the solar installers quoted me with this over IronRidge system and it piqued my interest. It's something that the installers used in my area (rocky ground) without the need of heavy equipment. Definitely something someone can do with a SDS it seems.

Osprey PowerRack™ - Ground Mount Solar | Nuance Energy Group, Inc.

The revolutionary innovation behind Nuance Energy’s ground mount solar racking system and the award-winning Osprey PowerRack™, is our utility patented earth anchor foundation system and the methodology patent used to install and pull “Load Test” earth anchors in real time soil conditions.

nuanceenergy.com

 

[MarkSolar]

One system I've been considering instead of ground screws is a system by Osprey. One of the solar installers quoted me with this over IronRidge system and it piqued my interest. It's something that the installers used in my area (rocky ground) without the need of heavy equipment. Definitely something someone can do with a SDS it seems.

Osprey PowerRack™ - Ground Mount Solar | Nuance Energy Group, Inc.

The revolutionary innovation behind Nuance Energy’s ground mount solar racking system and the award-winning Osprey PowerRack™, is our utility patented earth anchor foundation system and the methodology patent used to install and pull “Load Test” earth anchors in real time soil conditions.

nuanceenergy.com

Interesting, those are called duck bill anchors. I've used that style anchor to hold down fabric buildings, they work well. The only problem I've ever had is the stainless cable connected to the anchor corrodes and fails. Must have been a poor quality stainless.
It's not clear if you have to buy that load tester, rent it, or if it comes as part of the purchase.

 

[unhandled]

One system I've been considering instead of ground screws is a system by Osprey. One of the solar installers quoted me with this over IronRidge system and it piqued my interest. It's something that the installers used in my area (rocky ground) without the need of heavy equipment. Definitely something someone can do with a SDS it seems.

Osprey PowerRack™ - Ground Mount Solar | Nuance Energy Group, Inc.

The revolutionary innovation behind Nuance Energy’s ground mount solar racking system and the award-winning Osprey PowerRack™, is our utility patented earth anchor foundation system and the methodology patent used to install and pull “Load Test” earth anchors in real time soil conditions.

nuanceenergy.com

That looks pretty interesting. I'll ask for a quote on that to see what that looks like. Looks like something I could put together myself. Not sure about that load testing device though. Looks like a motor block crane with a a gauge attached to it. Not sure that would make sense to buy that for a DIY setup. We'll see what they say!

 

[harjms]

Interesting, those are called duck bill anchors. I've used that style anchor to hold down fabric buildings, they work well. The only problem I've ever had is the stainless cable connected to the anchor corrodes and fails. Must have been a poor quality stainless.
It's not clear if you have to buy that load tester, rent it, or if it comes as part of the purchase.

Yea it almost looked like you could rent it. Maybe schedule it for the week and ship back to them with the loading results? Seemed reasonable.

 

[harjms]

That looks pretty interesting. I'll ask for a quote on that to see what that looks like. Looks like something I could put together myself. Not sure about that load testing device though. Looks like a motor block crane with a a gauge attached to it. Not sure that would make sense to buy that for a DIY setup. We'll see what they say!

Agree. If the quote includes the loading device it seems like a pretty good deal. My issue with the screws or Dino tubes is digging 7’ holes and sourcing 21’ Sch 40 pipe.

 

[OzSolar]

Yea it almost looked like you could rent it. Maybe schedule it for the week and ship back to them with the loading results? Seemed reasonable.

We just did a few of these in rocky ground and it was not pleasant. Won't be making that mistake again.

 

[harjms]

We just did a few of these in rocky ground and it was not pleasant.

Oof. That’s not comforting. Did you use SDS or post driver?

 

[OzSolar]

Oof. That’s not comforting. Did you use SDS or post driver?'

Predilled with SDS Max. We ended up driving the rod right though the anchor when we tried to just use the drive rod. It was a nightmare.

 

[unhandled]

Off topic but I’m now wondering if I should go with a ballasted mount instead. Probably need to prep/level the ground at the block locations but that might be less expensive than 500-600 per helical pile. ?

 

[Zwy]

Off topic but I’m now wondering if I should go with a ballasted mount instead. Probably need to prep/level the ground at the block locations but that might be less expensive than 500-600 per helical pile. ?

It would depend on how large the array will be. My array, 32 feet x 16.5 feet tall. For the poles, it is 6 inch schedule 80 pipe with 2 poles. The force at the ground level in a 104mph wind rating is 72,000 lbs of force per pole. I have to bore a 36 inch round hole with an earth auger 7.5 feet deep according to the engineering specs and fill the hole around the pipe with concrete. That process starts next few weeks.

The issue with blocks in areas where it freezes is the frost will move each individual block up and down. A slab may be a better choice. I was at Grand Portage just a few weeks ago, the rest area for trucks had a solar array mounted to a floating slab, it wasn't just blocks. Frost will move the whole floating slab in one piece. Ok for smaller size arrays, can get cost prohibitive for large arrays.

Other choices are driven piles, around here the solar installers use a pile driver and drive an I beam upright into the ground. It works but I have seen some push up with frost, soil type could play into it. I assume they do drive below the frost line but haven't seen them drive the posts in. Pile drivers are not cheap but if you know someone you might get it done reasonable. It is fast.

Another choice would be to rent a small earth auger such as 6 or 8 inch, bore a hole below frost line and install pipe down the hole. Then fill the hole with concrete.

 

[peakbagger]

Its very soils dependent. Helicals and screw augers both have a tough time with glacial till full of rocks. Nothing really works with wetland type soils, its not just frost heaves, changes in ground water will seasonally heave the soil from far deeper than frost line. I had a recent project in area that was a filled in wetlands. There was 5 feet of fill on top of 20 feet of peat. The parking lot adjacent to it showed all sorts of signs of reflective cracking. It was a very expensive and time consuming effort to come up with something that would work to hold up a building. I also have had to deal with marine clay and the helicals had to go down 40 feet to get to the point where the it would hold anything up. In some cases it just makes sense to go with frame type structure supported off multiple piers and leave long anchor bolts to shim as needed every few years.

 

[unhandled]

I’m really pulling my hair now! Listening to people here, it looks almost impossible to ground mount solar panels! ?

I’m trying to avoid roof mount as my shingles are about halfway through their lifecycle.

Need to have an anti-gravitational mounts hovering above the spot!