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PRI Engineering Takes on the Brooks Solar II Project in Alberta

Brooks II Solar Project in Alberta

The Brooks Solar II Project is an expansion of the existing 17 MW Brooks solar farm on 200 acres of land located near the eponymous city of Brooks, Alberta. The initial Brooks Solar facility was the first ever utility-scale solar project for the province and generates enough clean energy to power approximately 3,000 homes. Brooks Solar II’s capacity adds an additional 27 MW and is expected to be operational for at least 30 years.

Brooks I

17 MW
48,582 solar modules
Nearly 3,000 tables of fixed racking
5,398 driven piles
8 Inverters

Brooks II

27 MW
73,268 solar modules
801 tables on single axis trackers
10,508 driven piles
9 inverters

PRI Engineering’s Scope of Work for the Brooks Solar II Project

PRI completed the following work for the solar project in Alberta

  • Pre-production load testing
  • Developed the issued for construction design
  • Completed onsite quality control and assurance

The Challenge:

  • Soft clay, with surficial saturated sand silt soils prone to frost heave

The Solution:

  • Innovative application of frost sleeves

Brief Synopsis of the Alberta Solar Project Design Process

The solar project was approved by the AUC in the early months of 2020 and Elemental Energy, the solar developer for the initial project, had the permits to move the project forward.

Before construction could start, a series of studies and environmental field tests were completed to better understand the terrain that this 27 MW project would be built on. Other pre-construction analyses were also completed to determine the impact the expansion would have on wildlife and wildlife habitat. PRI Engineering led the preproduction load testing to gather necessary data that would inform the solar foundation designs best suited to the site’s conditions.

The Challenges of Designing Solar Foundations for the Brooks Solar II Project

Subsurface conditions can influence the design of foundations considerably and it was already known from the previous Brooks Solar facility that the soil was clay-based and soft. For the expansion and given that the site covers 88 hectares, PRI Engineering needed to understand the overall gradation of site soils to help determine the requirements and properties for materials.

For the Brooks Solar II Project, PRI completed an Axial Load Test on the site to determine the amount of skin friction between the steel and soil. Unfortunately, results verified that the site subsurface comprised of soft soils, which added a layer of complexity to the project.

The threat of soft soils and frost upheave to solar foundation design for Alberta

The discovery of soft soils was not a threat to the viability of the solar project in Alberta but definitely posed a challenge to the design of the solar foundations. Soft soils mean that there is a risk of soils collapsing in over-saturated areas. This is often difficult to foresee as it results from extreme weather conditions. The amount of adfreeze pressures depends on the porosity of the soil, the natural moisture content, and the overall composition. Understanding soil composition is critical in determining the probability of damage that can be caused by frost upheave. It doesn’t end there. Frost heaving can lead to a slew of issues on-site, some even catastrophic. In a worst-case scenario, frost uplift that is not properly accounted for or addressed, can lead to the destruction of the foundation/racking system or even worst destruction of the PV modules.

What is Frost Heave?

Frost heaving is generated from the expansion of water and soil during freezing conditions. Soil is porous in nature with small voids between the granules and particles of soil. If these pores fill with water in freezing conditions, the soil will expand at about 9%. The pressure of the soil expanding is what generates frost uplift.

The Solar Foundation Solution: An Innovative Application of Frost Sleeves around the Piles

During PRI’s preliminary geotechnical analysis of the site, we found we needed to produce an innovative solution to address the threat of frost heaving. We knew that if this issue wasn’t addressed, it would eventually lead to unfavorable consequences, such as damage to the solar modules. We decided to try a unique take on a frost sleeve. Sleeves are placed around the piles, creating a smooth interface that would reduce the amount of friction between the frozen soil and the pile itself.

Testing the Solar Foundation Solution: Installing Piles On-site

The Brooks Solar II project, in its magnitude, would host thousands of piles on site. PRI obtained a sample size of about 60 to 70 piles to assess the effectiveness of using our version of a frost sleeve. The sleeves were installed successfully around each one of the piles and we are extremely satisfied with the results of our initial evaluation.

Next Steps for the Brooks Solar II Project

The Brooks Solar II Project is projected to wrap up in 2022. PRI is actively collaborating with the various working groups to ensure the project runs smoothly and will be providing additional support on the solar foundation design. Even with the challenges of collapsing soft soils and frost heave, our innovative solutions are getting projects to completion in Alberta and in Canada. As a general rule, taking a cohesive approach to addressing construction challenges is what is necessary to drive the industry forward, and lead efficiency and innovation. We are excited to see this massive solar project through to completion and are feeling energized about the next stages of this development. Stay tuned!

References

Elemental Energy (n.d.). Brooks Solar II Project – Project Newsletter. Retrieved on November 17, 2021.

Yazdani, A., Johnson, M. (2021). Solar Foundations in the Evolution of Renewable Energy Markets. Retrieved on November 17, 2021.

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