Featured on solarbuildermag.com. Interview by Solar Builder editor, Chris Crowell.
Solar sites are not the ideal parcels of flat land they used to be, so solar mounting and tracker providers have adapted systems to meet today’s tough terrain challenges. On this episode of The Pitch, we learn about the latest innovations in solar trackers, ground screws, wind tunnel testing, and solar project site planning — as well as the new TerraTrack 1P — from Chase Anderson, director of platform engineering for Terrasmart.
- 0:28 – Overview of tough terrain challenges for solar trackers
- 1:34 – New ways to overcome these challenges
- 3:28 – Explanation of slope analysis, ground screw tolerances
- 4:30 – 1P vs 2P TerraTrak trackers
- 5:54 – Piles vs. ground screws: Cost/benefit analysis
- 9:13 – How the latest research has changed tracker foundations
- 11:31 – Wind tunnel testing and tracker design
- 13:19 – How PeakYield protects against extreme weather
- 14:30 – Overview of SIFT, a new site optimization tool
Watch the full 17 min chat above, click a timestamp, or read through a partial transcript below.
SB: When we talk about “tough terrain challenges,” what are some of those challenges that you’re starting to encounter?
Anderson: As you said, a lot of the good terrain is no longer available, and so what we have left are sites that traditionally wouldn’t have been ideal for solar trackers. With these sites comes a lot of different grade variation across the site. You’ve got interesting subgrade or underground issues to deal with: rocks and cobble and all sorts of different soil types.
It’s really good to have a deep understanding of what you’re getting yourself into on these projects by researching early and upfront with more advanced geotech investigations. … Ultimately, labor is getting more expensive, and the cost of doing grading is rising quickly, so the idea is to let the product do most of the hard work and minimize the grading or completely eliminate it.
SB: Have we uncovered new ways to design or install systems that better solve for these challenges?
Anderson: There’s two parts to it: The product itself, and then the feedback loop that we get because we design the products, we engineer the products, we manufacture the products, and we build the products [in the field], ourselves. Our engineers are able to work directly with our construction teams to find out what could be better, what could we improve, what would make it easier.
We’ve found a lot of ways to innovate around the install processes and procedures. One way specifically related to the tough terrain is with the introduction several years ago of our leg algorithm — an advanced algorithm we use to set the leg heights based on the topography. It maximizes energy production but the real benefit is the installers in the field don’t have to make field decisions on the height to set the legs.
Example of leg adjustability
SB: Looking at the TerraTrak 1P, why the 1P over the 2P? You have both options. Is this due to the challenges from tough terrain?
Anderson: A lot of times, customers will come to us and they don’t have a preference. In those cases we use all the tools we have available to look at the cost of 1P, the cost of 2P, the layout itself. There’s several factors. In general, 1P tends to have a lower cost per watt, but it really depends. Our ability to offer both is nice. 1P is great for installers, it’s nice and low to the ground, easy to put together. We’ve done a lot of work to reduce the part count. 2P does pack more modules into a shorter length, so on certain site sizes 2P might make more sense.
SB: Is it fair to say this is more process innovation than product innovation? Seems with the data and the learning you have … you’ve obviously tweaked the product … but everything else that’s going into site planning and project planning is almost doing more than just the product updates?
Anderson: Very early on in the process we will do what’s called a slope analysis. We essentially use the same leg algorithm right up front when a customer provides topo so that we have the best understanding of what we’re getting ourselves into and can plan for that.
Our products are all designed to be highly configurable, so by doing that advanced slope analysis up front, we can select the right configuration and make sure the right pieces and parts are getting to the site.
There are things in the product that do make it unique, especially on the ground screw side. The ground screw tolerance is at grade whereas a driven pile is at the top of the pile, which could be four, five, six feet in the air. The result that we have to build the tolerances and the adjustability differently for ground screws than we do for piles.
The other piece is the telescoping leg that we have in the ground screw is just incredibly powerful at dealing with these terrain issues. So, it’s really a mix of both, and they work together.
SB: Terrasmart provides agnostic foundation solutions based upon each project’s needs, so I want us to look at the pros and cons of when it’s best to use ground screws.
Anderson: If you’ve got rock or really hard soil that you can’t drive into or you’d experience refusal with a driven pile, a ground screw is going to be a great option. The remediation options for driven piles can be quite expensive, and they can really impact your schedule quite a bit because the velocity of install is slow. For those sites, ground screws are an easy choice. The velocity is very predictable, even in the hardest rock.
It all comes down to the size of the hole that’s being drilled in the rock. For a ground screw, it’s very small, whereas a driven pile, if you’re doing like a drill and drive, that hole is at least six inches if not larger. That’s the obvious reason why you might use ground screws versus piles.
The less obvious is the frost heave issues that occur. When you drive a pile, you have to account for the frost heave forces. If you don’t properly account for it, over time, that pile will lift out of the ground. It can cause structural damage, module damage, micro cracks, all sorts of things.
The reason why the frost heave forces are so high on the pile is that its surface area is much larger, so you’ve typically got to go with a much deeper pile. We install a lot of projects in Maine with ground screws, and if we were to do those with driven piles, projects probably wouldn’t pencil out. The reason ground screws are so successful in handling frost heave is that the surface area is much smaller. I think it’s three or four times less surface area. So, the force itself is already reduced, but the threads always sit below the frost portion of the soil. All of our tension capacity comes from the threaded section, and we’re able to resist those frost heave forces pretty easily.
See a cost/benefit chart and the rest of Anderson’s ground screw vs piles explanation right here (8:22):
SB: I’m curious if the research or the data on anything that we’ve been talking about has changed in one way or another over the last few years. Are there new reasons to make certain decisions that maybe we weren’t making before?
Anderson: In 2016, we began testing with a piece of equipment we just call the test rig. It is a fully automated test platform for pull testing ground screws. It does a very detailed sequence of testing on a screw, (and generates) very advanced data recording. Every single test we’ve done, we relate it to geotech information that we have. So, when we get geotech reports for a new project, we’re able to look at those values, compare them to the ground screw database, and really we can determine if it’s a good fit for a ground screw or not.
The second piece is actually picking the right ground screw. They come in different lengths, and with different lengths of thread. Choosing the right ground screw is important, and that database makes that very easy for us to do.
Ground screws have a very predictable performance. If we know the soil type, and we know the torque that they’re being installed to, we can now specify a minimum torque value for each project individually based on its soil.
SB: Added into everything we’re talking about are wind loads and extreme weather risks … what is the most recent wind tunnel testing saying about optimal tracker design?
SB: When you’re talking about all of the front end work, working with a customer, and going through the different options, how long does this process take now? With the granularity that we’re getting into, is the data speeding up things? Are we trying to solve for so many things that it’s taking longer?
Anderson: The layouts and the site optimization and all that really has come from our SIFT product, which we use all the time internally and share with customers to use. That helps us select the best layout configuration, it helps us look at the terrain, and we’re constantly building more and more features into that product.
Our ability to go from learning the address of a site to first quote to final engineering package has just greatly reduced. Today, the moment that address is available, the request automatically flows through the system. A lot of the time-consuming work of getting the weather data, and all that is being done automatically. We’re able to turn around quotes same day or the next morning. And with the quote, you also get automatically generated CAD blocks, site layouts, full set of structural calc packages, construction plans, bill of materials. It’s all done right away.