Designing Pile Foundations for Solar Panels in Challenging Soils

Designing effective pile foundations for solar panels in challenging soils, such as loose or sandy terrains, requires careful consideration of soil properties, foundation types, and installation methods. Selecting the appropriate foundation ensures the stability and longevity of solar installations.

Understanding Soil Challenges

Loose and sandy soils present unique challenges for foundation design:

• Low Cohesion: These soils lack the cohesive strength found in clayey soils, making them prone to shifting and settlement.
• High Permeability: Sandy soils allow water to pass through easily, which can affect the foundation's stability, especially in areas with fluctuating water tables.
• Erosion Susceptibility: Without proper vegetation or stabilization, these soils are more susceptible to erosion, which can undermine foundations over time.

Foundation Options for Challenging Soils

Several foundation types are suitable for installing solar panels in loose or sandy soils:

1. Helical Piles

Helical piles, also known as screw piles, are steel shafts with helical plates that are screwed into the ground. They are effective in loose or sandy soils due to their design, which allows for load distribution along the helix. According to a white paper on foundation selection for ground-mounted PV solar systems, helical piles are preferable in sites with loose sand and high water tables, as they can achieve the necessary embedment depth without refusal.

Advantages:

• Ease of Installation: Helical piles can be installed quickly with minimal soil disturbance.
• Load-Bearing Capacity: The helical design provides excellent support in loose soils.
• Environmental Impact: Installation causes minimal vibration and noise, preserving the surrounding environment.

2. Driven Piles

Driven piles are long, slender columns made of steel, concrete, or timber that are driven into the ground to provide support. They are highly adaptable and can be used in various soil conditions, including sandy soils. Driven piles offer a reliable and cost-effective solution for both commercial and residential solar installations.

Advantages:

• High Load Capacity: Suitable for supporting significant weights, making them ideal for large-scale solar projects.
• Adaptability: Can be used in a wide range of environments, including sandy, clayey, and rocky soils.
• Efficiency: The use of pile drivers allows for quick and accurate placement, reducing installation time.

3. Ground Screws

Ground screws are galvanized steel screws that are drilled into the ground, providing a stable base for solar panel installations. They are particularly effective in loose or sandy soils and offer several benefits.

Advantages:

• Easy Installation: Ground Screws can be installed year-round using a variety of machines, making the process efficient.
• Immediate Load-Bearing: They can support the weight of solar panels immediately after installation.
• Suitability for Various Soils: Customized screws are available for different soil types and terrains, ensuring stability in loose or sandy conditions.

4. Ballasted Foundations

Ballasted foundations involve using weighty materials, such as concrete blocks, to anchor the solar panels without penetrating the ground. This method is beneficial in soils where penetration is challenging or undesirable. Ballasted foundations are good options where a combination of high refusal rates and low soil cohesiveness, such as loose sand with high water tables, are present.

Advantages:

• Non-Invasive: Ideal for sites where ground penetration must be avoided.
• Flexibility: Can be relocated if necessary, providing adaptability for temporary installations.
• Cost-Effective: Recent price declines in precast and pour-in-place solutions have made ballasted foundations more competitive.

Design Considerations

When designing pile foundations for solar panels in challenging soils, consider the following:

• Soil Testing: Conduct thorough geotechnical investigations to determine soil properties, including density, cohesion, and bearing capacity.
• Foundation Depth: Ensure piles reach a depth where the soil has adequate bearing capacity and minimal risk of erosion or shifting.
• Corrosion Protection: Use materials resistant to corrosion, especially in sandy soils with high salinity or moisture content.
• Load Calculations: Account for all loads, including the weight of the panels, wind forces, and potential seismic activity.
• Environmental Impact: Choose foundation types and installation methods that minimize environmental disturbance.

Conclusion

Selecting the appropriate foundation for solar panels in loose or sandy soils is crucial for the stability and longevity of the installation. Helical piles, driven piles, Ground Screws, and ballasted foundations each offer unique advantages tailored to specific site conditions. By conducting comprehensive soil assessments and considering the specific challenges of the site, engineers can design effective and durable foundations for solar energy systems.

‍