By Josh Von Deylen
Three natural problems that can have a major impact on any prospective solar project are unfavorable soil conditions, extreme topography, and a harsh climate. These three site conditions affect the design of a project and can drastically increase project costs. Previously, many developers walked away from difficult projects due to added costs from addressing disparaging conditions; in recent years, however, challenging sites have become prime candidates for solar projects. For developers and EPC’s, the keys to efficiently developing challenging projects include choosing the right racking manufacturer and collaborating effectively.
First and foremost, the largest exposure to potential increases in a project’s cost is the soil and subsurface conditions. While a geotech can give you information to start the development process, this is only a tool for determining the right foundation, and will give only a small glimpse of what truly lies beneath. Foundation options should be discussed and priced out in the initial quoting process so that both parties are aware of the quoted cost and implicated refusals after construction. Before a Purchase Order is placed, the racking venders should be required to do onsite pull testing and check the foundation drivability.
There is no way to know exactly how many refusals or subsurface items will be encountered, but testing clears up the ambiguity and mitigates construction risk and total project cost. Regions with good, stiff, clean soils, are desirable, but it is more likely that glacial till, cobble, bedrock, sand, or soft soils will be present. A driven pile or a micro helical would be the solution for ideal soil conditions. For areas loaded with rocks, cobble, or glacial till, a threaded ground screw with pre-drilled pilot holes is the best option. For sites that have small amounts of rock and cobble, but dense soils, a directly driven ground screw is preferred. Solid bedrock appears daunting, but it is no different than predrilling glacial till and driving in a ground screw. If a project has clean, soft soils, a high water table, and a deep frost line, a micro helical foundation is the best choice.
The second difficult site condition is erratic topography. Every solar developer dreams of a nice, flat area to build on. Unfortunately, the reality is that more curves are present than what one can see from a Google Earth image. Site walks are crucial to help reveal what the true topography is like. If it has steep rolling or north facing slopes, a topographical survey map should be completed to accurately portray the contours. Long rolling hills (5-10 percent grade) may not need special attention, but a site with smaller rolling hills (10-15 percent grade) may need some additional row breaks to accommodate the transitions. Adding extra foundation length and opening up the required tolerance for the front lip height is also a commonly overlooked item. For example, a flat site may have a 30” front lip height (±2”), where a high topography project calls for 36” (±8”) to be substituted in; this gives an installer 17” of extra room to roll with the grade. It sounds obvious while reading, but the hidden point is that this information needs to be baked into the plan before any racking is purchased. With a few extra dollars, extra row breaks, or longer foundation posts, you can save installers an extreme amount of time, and time is money!
The final conditions that a racking supplier can assist with are projects with varying climates. Developers today are no longer exclusively working in their backyards; they are developing projects coast-to-coast, from sun and sand to mud and snow. There are drastic differences between working in states with little snow or frost loads and working in states that have the opposite. High snow loads add an extreme amount of loading to the racking and foundation. This force demands more foundations to support the racking and distribute the extra load into the ground. Extra foundations mean extra costs (the difference in cost is shocking from 5psf to 80psf snow load designs) so it’s extremely important to work with a racking manufacturer early in the process to establish an accurate budget. Another cost driver, called frost depth, refers to the depth at which the ground is frozen during winter. Every county has a frost depth, or frost line, that must be taken into consideration for a foundation design. Deep frost lines are considered to be 30” to 42”, and all lines over 42” deep are considered extreme. Frozen ground will freeze to steel foundations and swell, pulling the foundation upward, which is why the design must account for it beforehand. For example, a driven pile in a 20” frost line may only need to be 6’ deep. The same foundation in a 42” frost line will have drastically larger loads requiring a depth of 8’ to 12’ or more. The best foundation option for deep frost lines is a micro helical anchor, because they can be driven under the frost line and easily resist the extra frost jacking loads. Rocky soil conditions prevent helicals from pushing past, but a rock screw is more than able; the industry standard is with two-thirds of the screw threads going past the frost line.
Every solar project offers unique challenges that demand engagement with racking vendors to guide developers to the right solution. As the solar industry continues to rapidly expand, ever more challenging sites will need innovative parties to collaborate effectively to complete more projects. Designing a project with the right foundation and racking in the early stages of development will guarantee the project is designed for buildability and budgeted accordingly. Partnering with a racking manufacturer with tested experience and multiple foundation offerings will provide the right foundation and racking systems to conquer any site.
Josh Von Deylen is Chief Executive Officer for APA Solar Racking, a fixed-tilt, ground mount solar racking manufacturer and installer in business since 2008.