Brian C. Boguess, Contributor
Innovations in solar ground mount foundations and racking systems have lagged behind the many evolutionary changes being made in photovoltaics, inverters, batteries and other balance of system technologies that together are driving down costs. Of course, there is not much that can be done to “enhance” a steel pile, a ground screw, rebar or concrete. Catching up will, therefore, require taking an entirely new approach to ground mount foundations. One promising technology is doing just that.
The earth anchor foundation system combines a proven device, the earth anchor (long used to anchor the guy-wiring that secures power poles), with an adjustable anchor stand in a different design that is less expensive and easier to install. In applications so far, the system is working well even under challenging site and soil conditions.
The result is the ability to deploy modular ground mount solar arrays virtually anywhere more easily, quickly and affordably than ever before, creating more opportunities in both residential and commercial projects at any scale.
How Does an Earth Anchor Work?
Like traditional ground mount foundations, such as piles and ground screws, earth anchors are set into and derive their holding strength from the soil. But there are two major differences. One is its small size and narrow profile that enables the earth anchor to be installed easily through a narrow hole in the ground using only a handheld electric or pneumatic hammer-drill powered by a portable generator or air compressor. The typical earth anchor has a bullet-like shape about 5 inches long and 1.5 inches in diameter with penetrating “teeth” at one end, a hole for inserting the drive rod at the other end, and an “eye” in the center for attaching a stainless-steel cable or galvanized rod.
The second major difference is the earth anchor’s holding strength based on the “inverted cone” effect of the contributing soil above, which enables it to work well in virtually all types of soil conditions. An earth anchor set to a 4-foot depth, for example, is secured by over 26 cubic feet of contributing soil for a holding capacity of over 3,000 pounds.
These design differences simplify the construction process, which begins by assembling the foundation’s modular platform on top of anchor stands, and placing it into position (See Image 1). The height of each anchor stand (the vertical parts with the base plates) is adjusted independently up or down using a handheld impact tool to level the platform as it is being assembled.
When the modular platform is in its final position — fully assembled, aligned and leveled — the earth anchors are set through a hole in the base plate of the anchor stands, usually to a depth of 3-4 feet below grade, depending on the soil conditions (Image 2, left). Each anchor can also be installed at an angle as needed to avoid underground obstacles. As each anchor is installed, a portable testing rig is used to conduct a load test, in real-time, to determine its actual holding strength (Image 2, right).
During the load test, uplift force is applied to the cable or rod attached to earth anchor, causing it to toggle and rotate into its final, horizontal and locked position. To ensure adequate performance, these tests are conducted to a minimum of 1.5 times the specified design loads. Should any test fail to reach its target strength, the anchor can either be removed and reinstalled at a different angle and/or depth, or a second anchor can be set with the load test then performed on the pair. After verifying the holding strength, the cable or rod is secured to the anchor stand.
This ability to conduct simple, inexpensive field load tests to measure the actual (vs. calculated) holding strength of all earth anchors reduces or eliminates the need for geotechnical reports and related inspections, and effectively assures being able to meet the design specifications with only minimal engineering.
After the platform is firmly anchored into the ground, the racking (not shown) is then attached and raised to the desired angle, and the solar panels are installed. This order of assembly makes it easier to place the testing rig’s tripod into position over each anchor stand.
For systems that must eventually be moved, or decommissioned and removed, the entire modular platform and solar array can be disassembled for use at another location. In projects that benefit from this “lift and shift” portability, such as providing temporary power during disaster recovery efforts, the earth anchor foundation system offers this significant additional advantage.
Earth anchors perform in rocky soil, sand, desert hard pan or limestone, over pavement or capped landfills, or in climates subject to freeze/thaw cycles. Installation into large rocks may require the use of a conventional expanding anchor bolt instead of an earth anchor, which is then secured to the anchor stand. But the remainder of the installation process remains exactly the same.
The earth anchor foundation system has been designed to overcome the many problems that continue to plague all other types of ground mount foundations. Its modular design and ease of installation make it possible for EPC firms to handle more projects more profitability.
Although relatively new, the earth anchor foundation system has been tested and deployed in the solar installations totaling about 15MWs of capacity in North America and the Caribbean. As a universal solution for all sites and soil types that is easier, faster and less expensive to use —from engineering and procurement through construction and, optionally, decommissioning — the earth anchor foundation system is destined to become increasingly popular with developers, contractors and distributors alike for ground mount solar projects.
Brian C. Boguess is the founder, president and CEO of Nuance Energy Group. Prior to co-founding Nuance Energy, Brian was an executive at SunPods, where he led sales and strategic alliances. It was his experience with solar market conditions, ground-mount engineering and construction requirements at SunPods that helped inspire the design of Nuance Energy’s Osprey PowerPlatform.