BUILDING FOR SOLAR GROWTH—SELECTING THE RIGHT FOUNDATION FOR ANY SITE

Solar builds are becoming more complex. “Perfect” sites with the ideal topography and terrain profile are less available, and sites that remain pose additional challenges for developers and EPCs alike. Selecting the right foundation is key to mitigating risks, overcoming hurdles, and constructing a project that delivers reliable solar power on budget and on time.

Solar power projects often deal with challenging terrain, which means it’s important to ensure the foundation is prepared so the array can have optimal performance.

What Lurks Beneath the Surface

The “right” foundation is a case-by-case decision. When it comes to terrain, it’s anyone’s guess what may be lurking beneath the surface. High-risk soils—including clay, bedrock, silt, and sand—are fraught with subsurface challenges, but even seemingly accommodating topography can have unwelcome surprises. Ground that hasn’t been touched in decades or centuries may be more difficult to penetrate than it appears, for example.

High-risk soil can lead to negative project outcomes, like pile refusal, which can push back project schedules and push up costs.

Preventing Worst-Case Scenarios

A foundation can make or break a project’s success—literally.

Fractured panels due to frost jacking. Mangled piles, damaged during installation. Delayed schedules, change orders, and over-budget expenses from a high rate of refusal. These worst-case scenarios are more likely to occur on challenging sites, but fortunately, they are also avoidable.

With a few strategic steps upfront, stakeholders can prevent the most common causes of foundation worst-case scenarios: pile refusal (failure to reach the needed embedment depth), frost heave and/or frost jacking (disruption of installed foundations due to frost conditions), challenging soils, delayed installation schedules, and cost escalations.

Step 1: Avoid Common Mistakes

Poor planning is typically the underlying reason for worst-case scenarios. More specifically, these common mistakes can throw a wrench in the works:

• Using the wrong frost depth in initial engineering calculations. A miscalculated depth can lead to uplifting foundations, resulting in expensive and time-consuming remediation.
• Not fully understanding the different soil types and how they affect frost heave that can cause refusal, and not engaging a geotechnical engineer to assess the subsurface conditions.
• Calculating frost heave loads that are too aggressive, which leads to over-engineering and higher material costs.
• Choosing a racking system or foundation type before engaging your installation partner.

Step 2: Set Your Foundation Up for Success

Part of selecting the right foundation is setting it up for success by following these fundamental steps:

• Get a geo-technical report—this is crucial to understanding the intricacies of the land, including subsurface conditions.
• Do pull tests based on the size and terrain of the site—a single test may not be adequate for assessing the full site.
• Review the project goals including budgets and dates—consider the impact of risks on your project goals.
• Run a break-even analysis for refusal rates and foundation options—some options are more expensive in the beginning, but may save you time and costs in the long run.
• Source foundations from a racking company that offers both screw and pile options to ensure you get an unbiased analysis that is best for your project’s site.

There are several steps that should be taken when building the foundation for a solar power project.

Step 3: Know the Pros and Cons of Each Foundation Type

Of the three primary foundation types–driven pile foundations, ground screw foundations, and ballast foundations–what may be a pro on one site could be a con on another. This is why carefully selecting the foundation type per site is important.

• Get a geo-technical report—this is crucial to understanding the intricacies of the land, including subsurface conditions.
• Do pull tests based on the size and terrain of the site—a single test may not be adequate for assessing the full site.
• Review the project goals including budgets and dates—consider the impact of risks on your project goals.
• Run a break-even analysis for refusal rates and foundation options—some options are more expensive in the beginning, but may save you time and costs in the long run.
• Source foundations from a racking company that offers both screw and pile options to ensure you get an unbiased analysis that is best for your project’s site.

Three common type of solar racking foundations—knowing which foundation to use in the right soil is crucial.

Driven pile foundations are the most common in solar development.

• Pros: They have lower costs upfront, work well in soft soils, and are relatively easy to procure due to the high number of manufacturers.
• Cons: There are risks of hitting refusals which require remediation, either a cut & drill method for unexpected refusals, or a drill & drive method for anticipated refusals.

Ground screw foundations are growing in popularity as sites become more challenging.

• Pros: They eliminate the risk of refusal, reduce frost-jacking, and have more predictable installation which keeps schedules on track.
• Cons: They require special machines for installation, upfront costs can be higher, and there are fewer experienced partners that offer them.

Ballast foundations are not as common as they are utilized when ground penetration is not a viable option on sites such as landfills and brownfields.

• Pros: They protect the sensitive membranes that protect landfills where ground installation is not possible.
• Cons: Installation requires pre-assembly, and they must be manufactured in a controlled environment.

Future-Focused Foundations

The benefits of careful foundation selection go beyond the initial build. The right foundation choice enhances the likelihood of hitting commercial operation date targets and generating revenue. An ill-suited foundation, on the other hand, can yield the cumulative effects of frost heave and frost jacking as each year goes by. Frost jacking can cause foundations to uplift resulting in undulating panels and cracks, and at some point the foundation may need to be replaced completely. Upfront planning can save a site from total disrepair down the road.

Ultimately, choosing the right installation company goes hand in hand with choosing the right foundation. An experienced partner will have deeper knowledge of putting strategy into action—how to respond to geotechnical results, how to understand the relationship of torque and tension when installing ground screws, what best practices aid refusal remediation, and so on.

Here are important questions to ask your foundation partner:

• How much experience do you have performing pull tests and analyzing geotechnical reports?
• What soil and weather conditions do I need to consider when selecting a foundation that is specific to my unique site?
• Do you have hands-on experience installing different foundation types?
• What is your remediation process if you encounter refusal during installation?
• What if both piles and screws are viable options – how do you advise your customers how to choose one or the other?
• Do you offer trackers and foundations as a one stop shop, or do you rely on outside partners?
• What’s your track record of success with each foundation type?

As sites become more complex for solar developers, a decision framework for choosing the right foundation can make even the most challenging sites a part of the clean energy transition and a solar-powered future.