Roundtable: Busting Solar Foundation Myths for Colder Climates

This online roundtable has past. We've added the video below for your convenience.

Join Arash Yazdani from PRI Engineering, Greg Rossetti from OYA Solar, Vishal Lala from Polar Racking, and Dan Carrocci from Determination Drilling Services for this lively roundtable on solar foundation design myths on June 7th, 2022 at 2 pm, EST.

The first myth we’ll bust in this webinar is that there is only one type of solar foundation for colder climates. In fact, depending on the region, the soil, and a host of other factors, you may be able to select a more cost-effective foundation for your large-scale solar projects in the Northeast US and Canada. Understanding your site’s conditions are one of the key paths to reducing the cost of your solar project. We’ll cover solar foundation design and a variety of other considerations when designing for colder climates during this roundtable.



  • Introduction to Panelists
  • Design of Foundation Elements for Racking Systems in Cold Climates
  • Common Foundation Solutions for Cold Climates
  • Economics of different Foundation Solutions
  • Q&A


Date: June 7th, 2022
Time: 2:00 PM EST
Format: Online
Presenter: PRI Engineering
Arash Yazdani, Director of Engineering, PRI Engineering
Greg Rossetti, Head of Land Acquisition, OYA Solar
Vishal Lala, Managing Partner, Polar Racking
Dan Carrocci, President, Determination Drilling Services

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Roundtable Transcript

Table of Contents

PRI Engineering Overview: Arash Yazdani

Determination Drilling Introduction: Dan Carrocci

Polar Racking Overview: Vishal Lala

OYA Solar Overview: Greg Rossetti

Guiding Principles: Design of Foundations for Solar Mounting Structures

What do you see from a cost standpoint to get these projects off the ground?

Geotechnical Investigations for Large Solar Sites: Finding Hidden Costs

The Pros and Cons of Helical Piles

The Pros and Cons of Ground Screw Foundations

The Pros and Cons of Micropiles

Question Period

Arash Yazdani: Welcome, everybody. Thank you, everybody, for joining us for Busting Solar Foundation Myths for Colder Climates.

Today, I have four guests with me to talk on this topic. I, Arash Yazdani, the Director of Engineering with PRI Engineering. Vishal Lala, the Managing Partner for Polar Racking, Greg Rossetti, the Head of Land Acquisition at OYA Solar, and Dan Carrocci, the President at Determination Drilling.

Today, we’re going to go through the design of foundation elements for racking systems in cold climates, common foundation solutions for cold climate foundations, and the economics of different foundation solutions. And then we’re going to finally end with a Q&A period.

Before getting started, we will let each speaker introduce themselves and their respective company.

PRI Engineering Overview: Arash Yazdani

Starting with PRI Engineering, we’re a team of 15. We have 100+ years of combined experience in engineering and consulting and construction management, which has allowed us to provide full engineering solutions.

Our specialization and our niche is the design of foundations for solar mounting structures, where we’ve completed over 200 projects in Western Canada, Southeastern Canada, Northeastern United, sorry, Southeastern Ontario, east coast Canada, Northeastern United States, and the sunny Caribbean. As well as all those services, we’ve also got an in-house concrete and soils lab in our Lindsay office, and we’re going to be expanding into other regions very soon. Stay tuned for some news on that. I’ll hand it over to Dan from Determination Drilling.

Determination Drilling Introduction: Dan Carrocci

Dan Carrocci: Hi, everybody. My name is Dan Carrocci. I’m the President of Determination Drilling. I’ve been running the business for 20+ years. We started as a geotechnical environmental drilling contractor, and then during the Feed-In-Tariff program in Ontario, we started expanding into renewable energy. Now that’s all that we do is build solar farms.

We’ve completed projects in every province and territory across Canada, literally every province and territory. So that’s a big milestone. I don’t believe there’s any drilling contractor in Canada that’s done that. Very proud of that. And we complete every type of foundation solution, which makes us different from every other drilling, piling contractor out there.

We perform driven piles, helical piles, ground screws, and bedrock micropiles. We have an array of remediation techniques that we can deploy to make sure that your site goes properly. We keep safety, quality, and production in mind with every single project, every single hole that goes in. And, of course, Determination Drilling, determination is in the name. So that’s us.

Arash: Thanks for that, Dan. Moving on to Vishal of Polar Racking, next.

Polar Racking Overview: Vishal Lala

Vishal Lala: I’m Vishal Lala, Managing Director and Co-founder of Polar Racking. We founded the company in 2009 so it’s our 13th year in business. We focus on fixed solar ground-mount, single-axis trackers, and solar carports. We’ve worked on projects all over Canada, the US, and the Caribbean.

We have a full in-house team, with geotechnical, structural, and mechanical engineers. In late 2021, we acquired Axsus Solar, which was a division of Magna Closures Inc. And we absorbed their single-axis tracker product line as well as their fixed-tilt solar ground mount line. And we now have the teams’ combined experience. We now have well over three gigawatts supplied.

Arash: Thanks Vishal, and last but not least, our friend with OYA Solar, Greg Rossetti.

OYA Solar Overview: Greg Rossetti

Greg Rossetti: Hey, everybody. OYA Solar was born out of greenfield development and has matured into an IPP with construction, and ownership of assets. I’m not sure what the total count is, but on the pipeline we’ve got, it’s over six gigawatts. Originally, with a focus on community solar, we were born out of Minnesota, and then we went into New York and beyond. And now we operate throughout North America, and Canada, as well.

Arash: Awesome. Thanks a lot for that, Greg, and the rest. Before jumping into our round table, I just wanted to give a brief introduction to the philosophy of the design of foundations for solar mounting structures.

Guiding Principles: Design of Foundations for Solar Mounting Structures

At the root of the process, it all starts with checking your regional conditions, which involves getting design parameters from the racking supplier, and also regional considerations, particularly, in the Northern climate, which is the focus of this webinar, as it relates to frost penetration and frost uplift.

Foundation Types and Considerations

When it comes to resisting these loads in your design, you have a multitude of foundation types to choose from and, there are a lot of different considerations that need to go into that. There’s the engineering piece. Constructability is also extremely important. If a foundation can’t be adequately constructed, it’s not the best foundation. It also has to meet the financial requirements. If it pushes a project over budget, it kind of defeats the purpose of the project. So, that’s got to be considered.

Adapting Foundations to the Racking System: Driven Piles

And of course, in this case, it’s got to be able to adapt to the racking system. As you look around the world, driven piles have always been the preferred foundation type for these types of systems. They’re cost-effective. They’re the simplest to install.

You can utilize a multitude of cross-sections. There are some benefits over some cross-sections over others. And we’ll dive into that a little bit more, a little later. Typically for sites with at least 10 feet or three meters of overburdened material. So that means 10 feet or three meters of soil overlying bedrock.

Ideally, there are minimally no obstructions. There is, however, some techniques and types of foundations that could be utilized to combat those type of things. And the foundation itself typically develops a strength from steel to the soil skin friction.

You’re getting resistance from friction between the ground and the pile itself. Before we go onto the next foundation type, maybe we can just go around the room, if there are any comments or anything anybody would like to add to that.

Driven Piles and Cost

Vishal: The one comment that I can make is that from a cost perspective, this generally tends to be the most cost-effective solution of all – if you can get away with using a driven pile. The other thing is, it’s also fairly easy to source because you’re looking at a straight round post or I-beam that you’re putting in the ground with limited secondary processes. So, for faster lead times, it also tends to be a favorable solution as well.

The Round Post versus I-Beam Debate for Driven Piles

The one thing that I would comment on, and pose back to you, Arash, and maybe you, Dan, is the round post versus the I-beam debate – since we’ve had a lot of talk about driven piles.

Dan: Before we get into it, let’s clarify that our job is to go in and test a project. When Greg shows up at a site for land development, he sees green grass and a flat site.

Driven Piles Easily Produce Straight Rows

He says, “This looks great for solar,” but we’re trying to figure out what’s under the ground and match the foundation type to the geology. So, one foundation is not necessarily superior to all. There’s no silver bullet solution. However, I do really enjoy driven piles, because you can get really nice, laser-beam-straight rows. They’re quick and easy to lay out.

Driven Piles Cost Less to Transport

The trucking itself, you have fewer transport costs because you’re able to pack the piles onto the trucks a lot tighter. And then add in the the quality of the installation.

Benefits of Round Posts for Driven Piles

Easier to Install and Lay out

Now when we’re talking about round pipe versus I-beam or H pile, I’m a big fan of the round pipe. Just because it’s a lot easier to lay out. You can roll it off the skids with the forks of your skid steer. In the install, there’s no extra access with an I-beam. You have to line up your flanges. They have to be laser-beam straight across, but a round pipe, if you hit a rock and it twists and skews, it’s okay, because it’s round. You don’t have to have it that perfect, flat, streamlined, all across. So, there are a lot of benefits to round pipe.

Can Install Frost Sleeves Afterward

They, after the fact, if you install the pile and it flies down faster than your drive time parameters, you can install a frost sleeve afterward to reduce the frost uplift forces.

I-Beam Foundations Require Planning

With an I-beam, you don’t have that luxury and you have to pre-plan it. You can’t wrap a frost sleeve around an I-beam after the fact. You have to pre-drill the hole, pre-wrap it, and install the pile. It’s a big pain in the neck.

I find a round pipe is just a very user-friendly foundation solution. They’re readily available. And they go in really nice with the right geology. That’s my take on it from the ground, from the fields.

Arash: Well, and thanks for that, Dan. I mean, that’s the key. That was one of the key things that should have been introduced is that, ultimately, there are a lot of racking suppliers out there.

Racking Suppliers and Foundations

Not all solar racking companies can accommodate every type of foundation. There are unfortunately, a lot of racking suppliers that say, “We’re the driven pile guys, or we’re the ground screw guys.” They only have one option – they’re a one-trick pony. And with that comes some constraints from a foundation standpoint. If you can’t match the subsurface conditions with your racking system, it may lead to some constructability challenges.

Dan: Yes, that’s right. It’s like, “Hey, we have to make I-beams work on this site. Because that’s all we can mount here, or we have to make a helical pile work, but there’s like a layer of sandstone or something, right?

Arash: Exactly. So, it’s not always conducive to the ground conditions and that’s where cost escalations happen on the construction side. There were a lot of benefits that Dan mentioned about the layout and the constructability, and then just the ease of working with a round post versus a W-section. The cost implications really come into play. If you’re dealing with a round post versus W-section, versus, which we’ll talk about in a second, a helical pile.

What do you see from a cost standpoint to get these projects off the ground?

Greg: I look at it as a bit of a funnel. So you’ve got some very high-cost items, and then you work your way through the funnel.

Solar Project Economics: Macro Concerns

Unfortunately, in this day and age, these projects are so price-sensitive that you do need to worry about the bottom of the funnel. Not as much as the top of the funnel, obviously, but you need to worry about the bottom of the funnel, or the projects tend not to pencil.

I’ll to try to paint the picture. There are panel prices, supply chain issues with racking, and everything that we’ve been dealing with over the last handful of years, policy issues, go through the list. I’ll put those as obvious sort of top-of-the-funnel-type concerns that we have when we’re looking at project economics.

Solar Project Economics: Minutiae and Technical Impacts

At the end of the day as well, you have to get into the minutia. If you don’t pay attention to the minutia, you cannot make the solar project work. Here we have more technical interconnection. Throughout North America, it’s becoming a massive challenge to find capacity available at a reasonable price and just understand that through the life cycle of a project. At what point do you conclude that “Hey, I do have a site that has reasonable capacity.” That could be a whole other sort of discussion just around capacity and the challenges that lie there.

Ultimately, as a solar developer and to Dan’s comment about the land acquisition standpoint, we see a nice flat site. That’s what we’re looking for, obviously. There are all those concerns throughout the funnel below the ground, financing, you name it, everything that I’ve just been describing at a high level. And at the end of the day, you have to find solutions for those smallest of price drivers.

And as you work through the funnel, subsequent challenges become more and more critical to the success of a project. When we arrive at Geotech, it finds its way in at a few points throughout the life cycle of a project.

First, you get to a site. If you’re working on bedrock, you know that you have a challenge. Shy of that you have a farm field, a hay field or it’s being row cropped, and you don’t know if you have 18 inches of topsoil or underlying clay for the next 20 or 50 feet.

Dan: Or building over mine fields

Geotechnical Investigations for Large Solar Sites: Finding Hidden Costs

Greg: As a solar developer, you may have a rough knowledge of the geology in the area. And frankly, I have that knowledge because of conversations over the years with people like you, Arash. Having a general sort of a view on where your Geotech’s going to land is important, but then you have to get into the final points.

Whether it’s a driven pile or micropiles, I’m sure you’re going to get to further in this presentation, it’s finding those economies where a 5-megawatt site or a 50, or something larger. You need to be able to look at these sites and say, it’s driven piles for this section. It’s possibly helicals here. It’s possibly something else in this area.

Flexible Racking & Experienced Team Leads to Successful Solar Project Economics

And having a team, like the team that’s sitting at this table, where you all have a level of experience, you don’t have to reeducate people from day one. So, you don’t need to reinvent the wheel with discussions. With that team, you can accelerate your way to a solution much faster. And you can come up with a plan, where we put driven pile here and  helicals here, maybe a combination.

For that you will need a flexible racking system. You need a contractor, a drilling contractor, who understands the nature of these types of projects to make them successful for a developer.

And if the developer’s not successful and the economics don’t pencil in and you can’t arrive at something that looks good in a spreadsheet, that you want to move forward and make the sizeable investments to get one of these things operational, none of us get to play at the end of the day.

The Cost Impact of One-Size-Fits-All Solar Foundation Design

Vishal: One other point, Dan, to pick up on your point about having driven piles in section A and then helical in section B. We have worked on a lot of projects, Arash and I, specifically where it was designed by others. They should have been driven piles in section A and helicals in B and then they just put helicals throughout the site because that was easy for them to design.

Dan: Yeah. A rubber stamp.

Vishal: Exactly.

Construction Impact of Poorly Designed Solar Sites

Dan: I have seen that with you, Vishal. That’s tough. As a construction contractor, we’re pulling our hair out. It just shapes the morale on the site. Everyone hates their lives and hates the job if the install is difficult due to the design. If the foundation works with the geology, it’s a happy, sunny day site, right?

So proper engineering, all starts right from the beginning, the preliminary site testing, the desktop study, geotechnical investigation, the pile load testing, and then the procurement. So, it’s in that order. That’s exactly what should happen to evaluate the site and evaluate your options.

Adapting Solar Racking to the Foundations: Cost-effective and Easy

Vishal: Some of the things that we’ve done, Arash and I, specifically on some of these sites is adapt the design to the foundations. For example, we know that there are driven piles in section A and a helicals in B. So, we’ll just design the rack to accommodate a round post. We’ll put a round-post driven in section B, and we’ll put a helical on A, so the top, the above-ground connection doesn’t change.

And then below ground, we’re putting in the right solution. That makes the most sense for the site and usually ends up being the most cost-effective and easy to put in the ground. That’s like one of the tricks in the toolbox. And I’m sure we’ll talk about a few more here, but I know that in those instances, that’s one solution we’ve generally done.

And then on other sites, we’ve seen a similar situation but with different foundation combinations. We’ve done ground screw in one section and a driven pile in another section or whatever makes the most sense. One of the advantages, we have with Polar Racking and our design is that we have a solution for ground screws, for driven piles, for helical piles, for ballast solutions. Our racking works with all foundation types.

We’re able to adapt to what the ground is telling us, rather than us saying, “Hey, put this in the ground because this is what we sell.”

Foundations Can Significantly Impact Construction Schedules

Greg: You’re both making me think about my little analogy about the funnel and the comment that the piles are the smaller things.

It’s the smaller things though that can become bigger issues. As you get further along in your development cycle and into construction, if you get some of those “small things” wrong, they can turn into some really big problems very quickly when you’re in the field. Because there’s no easier way to throw the wrench right in the proverbial spokes of a construction schedule, then to get your foundations wrong.

Dan: Absolutely.

Supply Chain and Foundation Issues

Greg: Because you have different lengths and different styles, getting those manufactured takes time. You don’t just go to Home Depot and pick them up. “I want the three-and-a-half-inch screw versus the four-inch screw.” You don’t have that, especially when you have challenging supply chains, like we have now, that just amplify, compound, pick whatever word you want, and make it a nightmare if you don’t get it right early on. You have to get it right.

You have to be as smart as you possibly can be going into it, and then you can deal with the smaller challenges that inevitably arrive. But at least those don’t cripple the schedule and then potentially screw up the project.

Cheaper Foundation Options May Run up Costs Later

Vishal: Well, we’ve seen a lot of people, who go for the cheaper option up front in the spreadsheet and then pay double to fix it afterward.

Greg: And lucky if it’s only double.

Vishal: And it’s usually much more though. We were working on a site recently where we proposed round posts because we knew that there were areas where you’re going to have to sleeve it. And that’s for sure, the right option. But like if you go with the W-section in that exact site, the sleeving becomes five times more or 10 times more. But people, they get caught with the shiny number upfront, so they just pay in the end. And that’s unfortunate – we see that happening way too much in our industry.

Greg: And you’re starting to sort of pull that thread there that maybe the cheaper solution will work. There’s a reason it shines. But if it’s got a 20% chance of working, you really got to think, do I want to go down to that?

So how much risk is there in that? How likely am I to succeed with that – with the lower cost solution versus what’s it going to cost me to pivot and switch gears down? So, if you have an intelligent plan, then you can take advantage of those cost savings. And that is my point.

The Right Team Supports Solar Design Risk Management

What you’re driving at, Vishal, is that if you have the right team, you can explore the minutiae of a project, the minutiae of your construction schedule, procurement, and all the rest of it to find those savings. But if you don’t have the right team and it’s across the board from Geotech to the major equipment supplier, your racking supplier, your foundation supplier – often part of that racking solution, and then your contract and if it’s on-site, it’s got to do the work.

Show up Monday morning and put the piles in the ground and put them in the ground at peaks. There’s a schedule and you got to put X number of hundreds of piles in the ground a day, or everything gets thrown off. That’s as I say, “You got to get it right.” And it can be right if you spend the time to figure it out.

Arash: And that’s the synthesis. I think like the message coming from the group is you need a team. If you have one out of four people at that table, saying, “This is the way,” and everybody else is saying something else. Chances are, it’s not going to work. And you need the developer’s buy-in, you need the racking company’s and the engineer’s.

The Limitations and Risk of One Foundation Type

You can’t have that one-trip pony. And in fact, too often or not, we’ve seen it. And both Vishal, all three of us, have brought it up where you have an install, or you have a designer that tries to design a site with one foundation type. The likelihood of you taking a 40–50-acre site and having homogeneous subsurface conditions is extremely unlikely.

Whether it’s 5%, 10%, 20%, 50%, it doesn’t matter, regardless of what that percentage of differences, if that hasn’t been accounted for in the design, you’re going to have 5%, 10% or 50% of the site, where those very large construction costs that both Vishal and Dan alluded to, throwing Greg’s spreadsheet out the window.

And suddenly, the financing of the project is that question because, what was originally financed, was, is not the reality. So, watch out for those spreadsheets.

The racking company should be able to accommodate the different foundation types. You need the engineer to be willing to look at designing different foundation types. And then you need a contractor that can accommodate installing different foundation types.

Different Foundation Types and Specialized Equipment

Greg: It goes without saying that as we rattle through these pile types, and you’ve got helical up now versus a driven. You got to know that when you show up at the site, whether you need a hammer or a screwdriver, they’re two very different tools.

And unfortunately, the types of hammers and the types of screwdriver equivalents that we use to construct these solar projects are not the kinds of things that, again, you can go pick up at Lowe’s or Home Depot. They’re specialized equipment that requires a specialized operator on top of everything else.

So just because you can jump in one of those excavators and dig a trench doesn’t mean you can jump in one of them and drive that pile in the ground, straight plumb, understand your torques, understand everything in that field to put that pile in the ground. That’s a whole another piece of the equation that sits with your contractor.

Quality Control on Solar Construction Sites

Dan: All that takes time to develop that team and the talents. We have been building a solar farm for 15 years. It took a while to get where we are – for people to truly appreciate the quality control that goes into it. As we’re installing these piles, whether it’s helical, driven or rock micro piles, you need to record the subsurface characteristics and relay that back to the engineers. Then they can look at that and say, “Okay, this is as per design.” If you don’t submit the quality control correctly, that pile never happened.

As with driven piles, we’re also recording time. We’re measuring every foot on the pile and literally there with a stopwatch, recording the time to determine penetration rates. With helical piles, we’re recording torque on a screen. So, for every pile, we will enter a pile ID number and the time we’d started installing that pile. As soon as that pile’s done, we hit stop and all of that gets relayed to the client afterward. So there’s a significant amount of quality control that can go into these projects. I am sure that people can truly appreciate what it is – countless nights, entering data into a spreadsheet.

Digitizing Quality Control for Solar Construction

Now that we’ve taken drilling into the 21st century, we’ve digitized everything. All our operators have iPads and they enter it all directly into their tablets. That way the client gets the information in real-time. The engineers get the information in real-time. They can assess that and evaluate the in-soil criteria right away and catch those, “These piles may need remediation before they get wrapped.” Often the racking crew is right on our tails. By digitizing everything, it works really well. I find it’s the way to go.

The Pros and Cons of Helical Piles

Helical Pile Installation Requires Expertise

Helical piles can range anywhere from a 14-inch to a 36-inch helical. We’ve seen up in Huntsville, Ontario, some really big ones. Obviously, the bigger the helix, the harder it is to steer in the ground. The helical piles, just by nature, are big clumsy things; they kind of wobble into the ground. It does take a lot of operator finesse to get them exactly where they need to be. However, they do have their place in softer soils.

You need that helix to keep the foundation settling, but also to resist the frost uplift. By having that helix, it’s just a big dinner plate, that’s going to keep that power where it needs to be. We run anywhere from 20,000-foot-pound heads to 90,000-foot-pound heads. So, as you can see like we turn our excavators into rotary heads into drills, and we’re able to spin these piles down in the ground.

Techniques for Ensuring Accurate Placement of Helical Piles

You need a ground technician at the bottom who’s guiding the operator. We set offset pins. That’s how we ensure accuracy. So, in a lot of these sites, we have to get that 20-foot-long helical pile within half an inch spatial distance for north, south, east, and west, which can be very difficult in the best of times. But our operators are so skilled, they can get them looking good.

Helical Piles and Shipping Costs

In the bottom right picture there, you can see the helical is on the truck. That’s why I was saying before is a helical takes up a lot of air space on a truck where a driven pile, that air space is gone so you could pack a lot more driven piles onto a vehicle, reducing your trucking costs.

Arash: We’re working on Dan’s honorary P.Eng.  Yes, he explains it pretty well. I think we’ve had several geotechnical talks over the years, so I’m definitely happy, that’s rubbed off. Just a couple of things to add. Typically, we’re using this in situations, seeing as the driven pile is the preferred foundation type. Once again, a lot of that is related to cost, but of course, we’ve got to meet the engineering requirements.

Frost Uplift and Helical Piles

We’ve got to, in these normal Northern climates, particularly, got to make sure that we can resist frost uplift. In these cases, as Dan mentioned, we got the dinner plate on the helical pile. As long as you’re able to adequately get the dinner plate into the ground without encountering boulders or cobbles.

Bedrock and Helical Piles

The other thing is you cannot penetrate a helical pile into bedrock, which is one major downfall of them, regardless of how soft the bedrock is. It’s just not feasible. You will not penetrate that layer deep enough. When you aren’t able to develop the adequate uplift resistance, this is usually option number two, but there is the transportation cost that Dan spoke to.

Manufacturing Costs of Helical Piles

And also, some of the manufacturing costs, that Vishal spoke to. That’s a challenge essentially around the driven post is a helical pile without the helical blade welded onto it. From a material standpoint, there’s not a lot of additional material, but that welding cost, that’s done by humans and, unfortunately, or fortunately, that’s an added cost to the foundation.

You could look at a helical pile, being anywhere from one and a half to double the cost of a driven pile from a supply standpoint. And I’d be curious, Dan, from an installation standpoint, is it kind of readily the same production rates, roughly the same kind of equipment, we have for support?

Installation Equipment for Helical Piles

Dan: Quite a bit slower, definitely a different skill set and equipment. For example, we would run our Gayk 6000 pile drivers for installing a driven pile. We did start making our own drill towers that mount onto excavators. Those are innovative pieces of equipment and we’re able to ramp up our production line on those.

Installation Rate for Foundations

We’ve been using them on a lot of testing projects and even production sites. So, like the helical pile, it is a good option. Our operators are lucky to get a 100 a day, and they’re pushing, pushing, pushing. 100 a day is really good if you can do that. I want to estimate about 50 to 75 per day on an average day. Driven piles, you could see 75 to 100, so I’d push it a little bit more to get an extra 20, 25 piles a day.

Helical Piles versus Driven Piles on Bedrock or Sandstone

The ultimate, as you mentioned, is when you can’t get into sandstone or bedrock with a helical pile. With a driven pile, I’d actually welcome that. If you can find a sandstone or a weathered rock layer within like 7- or 8-foot area, you can typically penetrate that with a driven pile, 2 to 3 feet and that locks your pile in better concrete – there is no popping that thing out. With a driven pile, you actually kind of want weathered rock, whereas with a helical, you’re just looking for soft soil. No boulders, no cobbles. If you do start getting into the boulder-cobble material, there is a remediation for that. You have to spin it out, dig, repack, re-survey, reinstall, which can be pretty costly and time-consuming again.

Cold Weather Benefit to Using Helical Piles

Arash: Just couple of other benefits of helicals – in places where they’re used is because of the round post. We’ve spoken this at large already.

Drawbacks to W-section and Frost Uplift

With the round post, you can mitigate frost with a frost sleeve, which is essentially a sewer pipe. When you got the driven round post, you can do the same, but the driven W-section, not so much. There is a product out there called Yellow Jacket. It’s very cumbersome to install. It requires doing some pre-drilling so that you could fit the pile with the Yellow Jacket.

Remediation and W-sections for Frost Uplift

And one of the challenges there, if you’re using it as a remediation method, is do you preemptively pre-drill every single hole, so that you can accommodate a remediation method. Then, you only end up utilizing 20% of those pre-drilled holes for remediation, or instead, do you use a round post and just simplify your life quite a bit more.

Production Rates and Driven Piles

When you’re dealing with helical piles, one nice thing—Dan touched on it, is the penetration rates with driven piles. Very similarly, you can do a correlation between the installation torques and the uplift capacity. You’ll have to typically utilize load testing to develop those correlations. That’s something we do quite a bit for a lot of customers, both correlating drive times to capacity and also, torque readings to capacity.

Dan: I’m sure that like those, you will find swings in those production rates, depending on the pile. If it’s a 6-meter pile versus a 1½ meter, I don’t think I’ve seen anything shorter than that. You’re going to get different rates, just so that people listening understand.

Weather and Production Rates

Greg: And the time of the year. If you start in the dead of winter, it’s too hard and you have shorter daylight hours. It’s just limited. There’s a lot of factors that go into that. Those production rates to your point. The weather for example.

Dan: Frozen finger, frozen equipment.

Greg This gets into whole other aspect of installing these systems. Good to go in when you’ve got one or two inches of frost and a skid steer or an excavator like that will run on top of the ground without punching through and sinking in.

But it’s easy to punch through an inch or two of frozen ground with a helical or any type of pile for that matter. But you don’t want to be in that field in the fall when it’s wet. You’re not putting one pile in.

Greg: A driven pile will penetrate the deepest frost 6, 7 feet. It’ll go through like a hot knife through butter. For a helical pile in winter, you have to pre-drill so there’s an extra cost. You have to pre-drill, but you also have to backfill that frozen material. So that’s tricky. Helical piles, as they say, they go in a little clumsy so you get a little gap around the pile. If water can penetrate that gap and fill it up, and then it freezes, that will artificially grab your pile and pop it even more. Whereas with a driven post, you’ll never have that little gap.

Dan: Right.

Greg: With the helical it’s important to go around afterward, fill in that gap with the existing material.

Impacts of Season and Weather on Construction Schedules

Dan: Yes, especially, depending on the time of the year, you’ll have that effect. It will be worse during certain times of the year, certain soil conditions versus others. And it’s again critical that you have the experience to know when you need to worry about it and when you don’t need to worry about it.

Yes, that’s just a lot of experience that goes into making those calls and making sure that you manage that construction schedule. To your point, the quality of the install and what you’re left with when the power guys leave the site and you’re a year, two, five years into operation.

Greg: It’s always a blue, sunny sky day. We’re finding out pretty quickly, such as working in Prince Edward Island, the rain out there, the weather, it’s every other day, right? We’re in Southern Alberta, there’s no rain at all. Like it’s just a sunny sky. You’ll be lucky to get a drop, although I think it is raining today.

Dan: And again, it impacts your production at the end of the day. Not all sites, not all piles, none of it is created equal.

The Pros and Cons of Ground Screw Foundations

Arash: That all makes sense. Next on our foundation list is ground screws. So, ground screws are pretty universal. Unlike the next foundation we’re going to talk about, which is also universal, they don’t require concrete.

Ground Screw and Subsurface Conditions on Solar Sites

Ground screws can be installed into very bouldery, cobbly geology, similar to the bottom right photo there. They can also be drilled into shallow, sedimentary bedrock. Of course, that’ll require pre-drilling. If you’re going into something with very large obstructions, it will also require pre-drilling. However, as we said, they’re very universal. One of the challenges with them is, of course, the size. In a lot of cases, they can go up to, well, theoretically could go as high as you wanted, but they’re typically, from what I understand, the economics of them kind of cap them out at about 3, 3½ inches.

Loading and Ground Screws

When you’re dealing with large wind loads and other bending movements that you have to resist from a racking system that may mean that instead of having one post, you have to go to two posts. Anytime you’re doubling your number of foundations, you’re typically doubling your potential for ground disturbance risk.

Cascading Effect of Issues with Installing Ground Screws

There are a lot more components that need to be aligned. Vishal can probably talk to this with respect to it. And both Dan and Greg have alluded to it throughout the conversation. This is step one. But if step one doesn’t go smoothly, you’re going to have a cascading effect down the line.

For example, If in every row you missed a pile because there was an obstruction that wasn’t considered in the design, you won’t have complete rows. All of a sudden, you can’t do your complete racking. You can’t do your complete wiring. Costs arise when you got to go back on a project and start backfilling, sending crews from the Southeast corner back to the Northwest corner because they wouldn’t adequately consider the geological conditions.

The Benefit of High Ground-mount Solar Racking Tolerances

When the foundations land in place, you need a racking system that can tolerate potential movements. Dan spoke to it quite a bit. It’s always nice when we have driven piles and laser beam rows. But when you’re dealing with helicals and ground screws, foundations tend to wobble, that’s where a racking system that can tolerate those differential movements and the adjustments needed to adequately correct a site, gets you to a successful construction project.

Vishal: Well, I do so appreciate the plug. Or the setup because we did design our site at the beginning. Most of the sites we were doing were helicals. So we did account for a lot of adjustment in our rack to accommodate and Dan has been a good beneficiary of some of that adjustability on site.

So, when there is a pile that’s off, you don’t necessarily have to pull it under the ground and fix it as long as the racking system can compensate for that – all the way through. We have made a lot of effort to make it a very constructable product. Just getting back to ground screws specifically, we’re seeing that a lot more.

Economics of Ground Screws

We’re doing a lot of projects in Maine, Massachusetts, and even in Ontario now, where we’re seeing ground screws are a great solution. They are fairly economical from a supply standpoint. But again, to Arash’s point, you’re putting in two piles instead of one. So, you have to appreciate that there is a little bit more risk there.

We can go pretty wide on the diameter. Although if you start going with a 5-inch or a 5½-inch ground screw, it’s equivalent to the price of a 5½-inch helical. So, you’re not necessarily saving on price there, but it still might be the right solution depending on the geology, for sure. Generally, when you’re pre-drilling and putting these in, we find that it is a good solution. Although, the pre-drilling definitely adds costs.

Dan: It’s a neater way to avoid concrete as well. If you’re in sub shallow rock conditions or that ground unconsolidated formations that keep collapsing on themselves. That’s where a ground screw comes in. So again, there’s no one silver bullet. Ground screws do have their place. Soft clays, they may pull right out of the ground. There’s not a lot of flight there, where that might be a helical kind of a solution, but this is a way to avoid concrete. If you’re installing in the winter, the last thing you want to do is have concrete trucks running around at minus 30. That’s not fun for anyone.

Greg: Or if you’re too far from a plant driving out on your loads, you don’t get eight cubic meters off a truck in 15 minutes if you’re that type.

Dan: A lot of work you’re doing on islands as in the Caribbean islands where there may not even be a concrete pipe there. Ground screws are a fantastic solution for that, given the friction in the pipe, without needing that concrete base, or the concrete matrix around it.

Avoiding Failure during Ground Screw Installation

In that bottom left picture, there is a helical or a ground screw failure. That’s where we were twisting into hard sandstone. And we achieved 9,000-foot pounds of torque and that’s where a 3-inch ground screw started to twist on itself. So that’s a situation where we said, “Okay, pre-drilling, that removes quite a bit of that resistance.” Now we can get the pile down to depth with  a 7,500 to 8,000-foot pound torque. That’s where pre-drilling, I put that picture in there intentionally because yes, you can have pile failure if your torque gets too high, but pre-drilling is a good way to minimize that.

At a pre-drilling, you just run about 3½ inch or 3 inches over diameter, down-the-hole hammer. It’s a rotary percussive method and it will go through all those cobbles, bedrock, you name it, even soil, sand, and clay. I know you don’t like calling it dirt, right? Your last podcast was, “It’s Soil, not Dirt.”  A down-the-hole hammer is a fantastic way to make that pre-drilling hole and then you just twist in your ground screw afterward. And again, you report torque similarly to the above.

Testing Helps Avoid Pile Failure During Construction

Vishal: One thing I want to pick up on what you said Dan, I’ve learned this from Arash more than anything is that failure is great – well, not great, but it’s not a bad thing when you’re testing. You want to know what fails. You would rather fail on five ground screws during testing than roll in there with 50,000 screws and then start like snapping piles.

Dan: There is no such thing as bad data.

Arash: Exactly. And that’s just it. The whole, main objective is to fail during pre-production. As we go through the foundation design process, you start with a geotechnical investigation, understanding what your subsurface conditions are, whether that’s test bits or boreholes. Then you move into the pre-production testing program, where you are testing the different foundations that may be conducive to the proposed geology. Finally, you go into production. Once you go into production, you’ve hopefully worked out all the kinks. You’ve figured out your foundation.

Uniformity of Foundation Types across Large Solar Sites

Typically, on most sites, probably about 80 to 90% of the site can be used with one foundation type. Maybe you are using a slightly different helical size or helical blade. Maybe you’re using a slightly different embedment depth or thread depth for ground screws, but there are minor adjustments. But then in that last 10, 20% is where you lose the cost or lose the momentum of the project.

Contractors Will Take Advantage of Design Flaws

And if you don’t have that properly accounted for and quantified up front, that’s a contractor’s dream. A contractor told me a couple of weeks ago that their job is to find the holes in the design and a good contractor will find those holes in the design. And it wasn’t Dan, it was outside of solar. They will find the holes in the design and they will change the order of the project. And that’s unfortunately, a lot of cases.

If you have a cheap install price, that’s something you got to be thinking about, “What are the repercussions when this goes wrong? How do we fix this? What are the associated remediation costs?”

The base cost may look great but if you’re unlucky, you triple or quadruple the foundation cost. All of a sudden, somebody like Greg is pretty frustrated because his really good site isn’t generating the return on investment that he needs.

The Value of Geotechnical Investigations on Solar Sites

Vishal: I think an important point is that the company that you’re hiring to do the testing understands the end product. PRI Engineering highly focuses on solar, number one, they know the different types of foundation they can use, but number two, they understand what’s going to happen during install. Think in terms of the scale. This is not a building where you’re going to put six foundations but a farm where you’re going to put tens of thousands of foundations potentially. You need to figure out the constructability as well as the design when you’re doing the testing. I think that’s a lot of value you bring to these projects.

And then, you need to figure out how the foundations interact with the rack as they’re going to build.  That’s something you learn after working with the PRI or Determination Drilling that understands kind of both sides of the coin, for lack of a better description.

Dan: We are pretty dialed in. We’ve tested hundreds of projects across Canada and, all of them have gone flawless just from pre-project planning to being ready for the what-ifs. Having that geotechnical knowledge from my side, from your side. I don’t if anyone knows, but Arash and I have worked together for 15 years building bridges, roads, schools, hospitals, you name it, doing site investigation work – really complicated projects.

Now, solar is just as complicated and we’re dealing with a huge landmass in a cold climate. So that’s tricky and clear across Canada, coast to coast, every province, every territory. So, it’s important to have that diverse team that understands the challenges of constructability.

Vishal: We’ve seen other Geotech reports that, you can tell, don’t have an appreciation for solar and the non-repeatability of what they’re about to embark on. The foundation designs don’t necessarily make sense for the end application, because they don’t have experience building a manufacturing plant in a field type of mentality.

Greg: That’s exactly what it is. We’re trying to arrive or we’re trying to achieve manufacturing efficiencies in an environment where you don’t have a roof over your head and mother nature can do whatever she so chooses to do with your site.

And that’s an added challenge that solar has over a hospital, a school or any other type of building. There you have a narrow, deep foundation versus a broad, very wide, shallow foundation, which introduces what I just described, mother nature, more so than in any other type of construction project, when sticking to a simple comparison.

The Pros and Cons of Micropiles

Cost and Micropiles

Arash: We’re just going to quickly talk on micropiles. We’ve already indirectly talked about micropiles.  Greg, Dan, and Vishal all alluded to the expensive cost related to concrete.

Concrete and Micropiles

One of the bigger challenges with micropiles in Southern Ontario, in particular, is that a lot of people have heard a lot of horror stories about the failures, and a lot of them were associated with micropiles. Many people know that Ontario was the kind of original home to solar in Canada. One of the big misconceptions is that more concrete is better. However, more concrete in the wrong region of the foundation is not better. In a lot of cases, what was happening was that you were getting collapsing soils in the frost zone, and they were filling the micropiles right to the surface.

Essentially frost uplift occurs when the ground freezes. The water in the pores of the soil freezes, expands, and puts an adfreeze pressure on the pile. So that’s dependent on the surface area. If you increase that surface area, then you have more frost uplift. Often, these foundations were being installed, not as per the design. To the last point on the slide, completing QA/QC is extremely important.

That’s one of the key things. I can’t describe how important QA/QC is through any of your foundation types. In a situation like this, unfortunately, we saw a lot of failures, because of people placing grout and concrete-

Dan: Presence of groundwater too.

Arash: The presence of groundwater. Yes absolutely, collapsing soils-

Dan: Groundwater, or tremie construction.

Arash: Tremie. Yes, we’re talking of specialized construction methods all of a sudden.

Dan: In the dead of the winter, if the site is 26,000 bedrock micropiles. That’s a lot of rock drilling. And when you hit water, it adds a whole other ballgame. The difference between a 10-inch hole and a 12-inch hole is your penetration rates slow down. You’re also using quite a bit more concrete. But a larger hole does allow you some room to get your pile plunged into the perfect location. It does help with your pile accuracy. With a tight wall, you’re using fewer materials, but it can be a lot more difficult to get that pile where it needs to be.

Arash: Staying on the theme of concrete, ballasted foundations, these are probably considered the most expensive, and most typically used in landfills. If you’ve got a capped landfill, it’s pretty common to use a concrete ballast solution.

It can be pre-cast or cast-in-place. In areas where you cannot penetrate the underground, like a landfill or on sites where you get uncontrolled fill activities, the ground pressure that’s placed on the ground from these structures is very minimal – very low load.

So, you’re able to control the settlement a little bit with this type of foundation, and you don’t enter into the ground risks that are associated with going below grade. However, the initial cost is probably double, but it’s a little bit more guaranteed. That’s where you don’t see a lot of these foundations except for landfill sites, right.

Dan: Carports.

Arash: Carports, exactly, where you have fewer foundation elements. We’ve talked and we’ve touched on remediation a little bit. We’ve talked about the last 10%, we’ve talked about frost sleeves, and we’ve talked a little bit about adfreeze.

Frost sleeves reduce that adfreeze pressure. Think of it as an interface between the pile and the ground that will reduce the overall friction between the ground and the pile. Insulation can also be utilized. That’s very expensive. Think about rigid foam insulation that you would put on the outside of your foundation wall.

You would create a dance floor around the pile with that material. One last remediation is utilizing a different foundation type. And before I jump into that question, I’m going to go to one of the questions I was asked during the conversation.

Question Period

When recommending combination foundations, mixed driven piles, and helical piles, do you prefer it split according to solar panel sections more broadly? Or can we determine based on geological conditions more closely?

Absolutely, we want to look at the geological conditions. In a lot of cases, there’s going to be what we call a transition zone between one major geological deposition and another major geological deposition in which we had to draw a line in the array so that they could make a procurement. But we all know that line that separates zone A and B is a little bit gray. In those cases, we might propose a driven pile up into the line, but we find that the helical is required a little bit further south from that line.

So, utilizing different foundation types is often the way to go. If you have a different mix, the ability to balance your foundation types, and sometimes it’s hard to digest, may be an added cost of going out and buying an additional foundation element. However, overall, you’ll probably find that the cost is going to be less at the end of the construction.

Dan: During production, where if we’re working down a row and we start seeing low torques, we’ll stop. After two piles, we’ll go to the opposite end of the row and work towards it.

And then, as soon as we find that soft zone again, that’s where we’ll stop. Then we can infill that area with a larger helix or whatever it may be. So, we’re delineating during production as well. I treat every pile like a data point, as you mentioned like auto manufacturing.

We have total quality management with upper control limits and lower control. It’s more trying to narrow that rate down to the middle, so you have the least amount of waste. I treat it as a manufacturing line with a total quality management, a Six Sigma type of approach to it, which is hard to find in drilling. Most drillers just stick a pile in the ground. We take a different approach to it, for sure.

Have you seen any limitations of compatibility between common trackers and ground screws or helical piles?

Arash: There’s one last question, before we wrap it up or maybe one more question after that.

Have you seen any limitations of compatibility between common trackers and ground screws or helical piles?

And, I’m going to probably just put that right over to Vishal. The key is that you’re selecting a racking supplier that can accommodate different foundation pipes because you never want to pigeonhole yourself to one foundation type.

Vishal: Yeah, exactly. And we didn’t plant this question, but in hindsight, I might have. So, we do have our tracker at Polar Racking here which is the Axsus Solar Tracker. It can accommodate ground screws and helical piles. And a regular driven, like I-beam type solution. Just the fact being a Canadian company and working with the geology up here and supplying a lot of projects in the Northeast, we recognize very quickly that one, we need to accommodate these different types of foundations because your typical tracker company is kind of looking for those sweet 700 megawatts, 1-gigawatt sites, where the ground is pretty flat and homogeneous, and there’s not a lot of frost, so you won’t necessarily need a screw or helical pile.

But most of our projects, we’re doing lots of projects now, like community solar projects in New York, 7 megawatts at a time. Like we’re doing a few dozen of those right now, but ultimately there are 7 megawatts at a time and we’re using driven piles and ground screws on those sites depending on the site.

And so yes, we can accommodate varying topography as well, varying ground conditions with again a multitude of foundation solutions here.

Greg: It’s called ground mount solar and the most challenging part about it is the ground. It is a civil project. Although the end-use is electrical, a ground mount solar project is all about civil that can make or break the project is what’s under the ground. So proper pre-site investigation is critical. Proper installation practices are critical. It’s going to make it– It’s just like building a house. If your foundation is off, your racking installers are off.

Your panel installers are off your project as well. Our goal is to get the project started on the right foot to match the foundation to the geology. Again, all these are good viable solutions and it’s critical to have like every tool in your box available. I want to thank everyone for coming out.

Arash: We did have one last question come in. And it was a heavy design foundation for the reclaimed mine site.

So, Carl, I have looked, currently working on a reclaimed mine site in Alberta. And if you’ve got some questions about that, maybe you can reach out to me separately, or I can reach out to you and we can see if there’s some way to help you. And if you’ve got a project that’s got those conditions. Unless there’s anything else, thanks again, to all the guests, Greg, Vishal, Dan, and as Dan mentioned, the behind-the-scene team, we would be nowhere without them, so much appreciated.

And of course, thank you to all the viewers for joining us this afternoon, and feel free to reach out to any of us, if you’ve got any further questions.