A Terrasmart Innovation Engineer looks at ways to overcome weather challenges, especially when installing solar in Midwestern states.
Freeze freeze is one of the most common problems in the Midwest and especially in Illinois, which is prone to freezes due to the combination of bitter winters and unique soil composition.
Because frost heave is the process by which soil expands after it absorbs water and then freezes, Illinois and other states with periods of freezing temperatures for extended periods are especially vulnerable. It’s not possible to completely prevent the physics of frost swelling, but it is possible to prevent it from wreaking havoc on solar sites even in the dead of winter.
Nearly all soils can heave, but certain soils are more susceptible than others, such as variegated clays and other fine-grained brand sediments common in Illinois. It is also important to understand the rate at which the soil can heave, dictated by its grain size, structure, permeability and capillary flow. Locations in Illinois often have more than one soil type in the same location, and the design and installation must be adjusted accordingly.
Installations in Illinois can be tricky. The Midwest usually has loose topsoil, but there may still be boulders, rocks, and cobbles hidden even if it has been used for agriculture for years. Frost depth also has a significant impact on foundation design, and Illinois winters can produce frost depths of more than five feet. Developers face all of these considerations, on top of the variations in slope and undulating terrain.
Most vulnerable locations
A common mistake in weather mitigation is focusing on one part of a timeline. Sites can be vulnerable from the planning stage until years after operation.
In the planning process: Before a site is developed, failing to adequately assess soils or topography or making incorrect assumptions about frost depths or snow accumulations can lead to vulnerabilities.
During installation: Refusals occur if a stack takes longer than five minutes to install or if it does not advance 12 inches within 30 seconds. During installation, conditions that lead to frost can also lead to rejection risk, which in turn leads to project delays and budget escalation.
Over time: Even if a site functions successfully and without incident for a year, it can still be vulnerable to frost over time. The growth of ice lenses can cause the soil to freeze at the foundation, a process known as adfreezing, and create an upward heaving force. If a site is not developed with the variety of unique site conditions in mind, frost frostbite can occur years after installation.
How to make a site frost-proof
Frost heaving means taking a unique approach for each location, following these steps:
Rate the location: Even though silt is a common soil in Illinois, there may be other soils mixed in that add to the complexity of a site. Developers and EPCs can protect a site by reviewing a soil properties report and rejection risk estimates. In other words, decision makers must conduct careful tensile testing at multiple locations on the site and complete extensive geotechnical assessments before proceeding with installation.
Build a strong foundation: If a developer and/or EPC selects a foundation before choosing a scaffolding partner, they may miss critical assessments such as subsurface issues that determine appropriate foundation options. One of the biggest foundation questions in any site planning process is piles versus ground screws. Ground screws are ideally suited for deep freeze areas, are typically more cost-effective and quicker to install, and guarantee the best long-term reliability. However, there may be unusual circumstances that make stacks a better choice. A racking partner can offer a breakeven analysis to help determine the best location approach.
Prepare for snow loads: Most frost considerations focus on what’s happening in the ground, but preparation for snow loads is also important. Racks that are not designed to withstand snow loads can weaken the foundation, increase costs, decrease productivity and shorten service life. Preparation for snow loads can include tilting the module, a higher front of the module, reinforced material and an individual table-based design approach.
What to ask
With all this in mind, developers can protect their sites by asking a partner these questions about their expertise and experience.
Frost rise
- Where do you get your adfreeze and frost depth values from?
- How do you calculate frost loads and forces?
- What is your process for conducting soil analysis?
- Have you worked in locations that have experienced frost, and if so, how have they performed in the long term?
Snow loads
- How do you calculate the snow load for a project?
- What is the heaviest snow load you have installed?
- How do you track the weather? Do you have trackers with snow sensors and snow sanding functions?
Topography
- What slope tolerance can you take into account?
- What slope tolerance did you install?
- Is your rack adjustable during installation?
Installation
- How many foundations do you plan to install per day, and what is the basis for that assumption?
- Have you considered denial risks and costs during the planning phase? How did you arrive at these results?
- Where have you installed projects? How familiar are you with the regional and local specificities?
- What are the steps you are taking to make installations more predictable so that costs and timelines don’t escalate?
While solar energy in Illinois has some challenges, these conditions are solvable with careful assessments and customized developments and installations. Because frost can occur even years after the date of commercial operation, it is wise to consider the long-term ROI and reliability of racking systems, not just the upfront costs. With weather and freezes at bay, Illinois is ready to continue its national leadership in utility-scale solar and the clean energy transition.
Ameer Abuhamdeh, currently working as an Innovation Engineer at Terrace martbrings experience in product development and mechanical engineering to his five-year tenure at Terrasmart. His wind tunnel and product testing has provided innovative solutions for Terrasmart’s ground mounting systems team. Abuhamdeh graduated from the University of Cincinnati with a Bachelor of Science in Mechanical Engineering.
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