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German inventor Klaus Krinner, who created a Christmas tree stand that bears his surname in 1987, was given the humble task of erecting a pole in his yard to hang laundry. Not only did the laundry pole stay upright, but another grand invention came about — the first Krinner ground screw. Today, ground screws are a common foundational choice for construction projects. They are used for signage, lights, utilities and buildings that are two-stories or less. The ground-attached mount has also gained traction in the large-scale U.S. solar market as PV projects enter territories with hillier landscapes and challenging soil conditions. “For us it’s perfect, because we shine when the ground is tricky,” said Enmanuel Rumbos, chief strategic officer at Krinner Schraubfundamente GmbH. The modern ground screw didn’t originate in solar construction, but Rumbos said it was validated by it. Krinner — not the company producing ground screws, but its founder — sought global patents on the foundation after it was deployed in one of the first substantial solar projects in Germany. Those patents eventually expired, and the market has proliferated with manufacturers producing their own ground screws, many coming from China. A few others, Krinner included, have started producing ground screws in the United States to reap the benefits of domestic manufacturing subsidies from the Inflation Reduction Act. Threading its way into U.S. solar construction I-, C- or H-beams still dominate solar piling choices due to their cheaper production vs. ground screws. However, depending on the project site, ground screws have an edge that can make more economic sense than beam piles. When an I-beam is deployed in challenging site conditions, there is a higher chance for refusals. The beam itself could be much longer compared to ground screws, which can embed at shorter depths and better react to frost heave. APA Solar Racking of Ridgeville Corners, Ohio, started out producing helical piles, a driven foundation with two to three curved threads that are designed to resist frost heave. Seven years ago, the company started carrying ground screws and recently began manufacturing them domestically. APA found that both ground screws and helicals largely use the same equipment for installation and undergo the same push, pull and lateral load tests for deployment. The primary difference is that ground screws have a much larger threaded portion than helicals. Ground screws, which resemble the common wood screw, started gaining more traction as the New England market opened to large-scale solar projects. Northeastern soil is rife with glacial till, cobble, boulders and bedrock — ideal conditions for ground screws. “There’s just no other type of foundation out there that can do something similar to a ground screw,” said Josh Von Deylen, CEO of APA Solar Racking. Terrasmart, a turnkey solar racking manufacturer and installation service from Fort Myers, Florida, was an early adopter of ground screws for PV projects in the United States and a longtime client of Krinner. The company has tested and catalogued each project it has installed, resulting in a data log of 12,000 tests on ground screws and a standardized method for installing ground screw projects. Before installation, a geotechnical investigation is made on a project site. Installers perform a pull test in the soil to determine the proper depth for ground screw embedment. Ground screws are installed by drilling pilot holes and are later drilled into place with a pile driver or other specialized equipment. To optimally work on a project site, ground screw threading must be driven below the frost line, otherwise there’s a risk of frost heave. Having smaller threads means ground screws can work around subterranean obstacles. If boulders or bedrock are on a project site, a pilot hole is drilled into the rock, filled with aggregate and the ground screw is driven into the hole and secured. “Bringing a ground screw in on those sites is a much more predictable performance,” said Chase Anderson, director of engineering at Terrasmart. “The ground screw really is the product that you put on sites that traditionally might not have been right for solar.” Taking large-scale projects to new heights A driving trend among solar trackers is making these moving solar racks work on uneven landscapes. Solar trackers have taken on new shapes with articulating posts that will follow the contours of project sites, but hilly land often comes with obstacles beneath the surface. “In the past, a tracker project is on a nice, big, flat field. There’s a reason why they’re flat. The geology of them and the soil is usually pretty good,” Von Deylen said. “The industry is growing so much to the point that solar cannot just work on flat sites. Better locations might be high topography, where people are not farming, or there is rock and cobble in there.” So, the foundations of solar trackers have had to change to adapt to these project sites, garnering new demand for ground screws. In 2021, APA Solar Racking introduced its A-Frame Tracker Foundation, an A-shaped mounting structure that uses ground screws and works with third-party single-axis solar trackers. That same year, Terrasmart debuted TerraTrak, its foray into solar tracking, which uses an A-frame-style foundation supported by ground screws. Nextracker acquired ground-mount manufacturer Ojjo in 2024 and is using its Earth Truss foundation on tracker projects. Earth Truss uses two threaded posts, like ground screws, that are driven into the ground at a 45° angle. Ground screws might not be the inexpensive choice for every solar project, but they’re a better option to make an array work on challenging sites with uneven surfaces and obstacles underneath. A ground screw can hold a laundry pole in place in a yard just as well as it can secure a solar project to a mountainside — all thanks to Klaus Krinner. |
