U.S. Virgin Islands Solar Project Gets Hurricane-Proofed by Polar Racking
In a devastating hurricane that hit the U.S. Virgin Islands in 2017, a 4MW solar project that powered several local communities was destroyed and uprooted from the ground.
Polar Racking won the contract to supply the new solar foundation and racking systems for a couple of reasons. First, our knowledge and experience we’ve gained from the harsh weather in North America transfer well to designing for the extreme weather in the U.S. Virgin Islands. Second, we let the site do the talking and recommend foundations and racking that will perform well under those particular conditions.
In a nutshell, designing around extreme weather means you are taking into consideration the environmental factors that stress the ground-mount system. When planning solar ground-mount foundations for North America, we account for high wind, snow, rain loads, and uplift or heave factors that can be caused by extreme temperatures. For the Caribbean, the primary stresses on the system include hurricane-force wind, impacts from debris, and material degradation from saltwater.
To determine the ideal foundation and racking system for this site and project, Polar Racking collaborated with the leading experts in North American and the Caribbean, PRI Engineering, AltaPro, and Williams Solar, for solar ground-mount design and solutions. Since it was a reconstruction, we had the advantage of reviewing the failure points of the previous system. In brief, some high impact failure modes include racking design for high wind, foundation post overturning, and small components. For more information on extreme storm conditions and solar systems, we recommend reading the thorough report written by the Rocky Mountain Institute. All of which we can solve by ensuring that our entire system from foundations up will perform in the site-specific conditions.
After extensive research, we decided to use ground screws as the pile type and are on-site with the Field Technicians from PRI Engineering to ensure a smooth installation.
One principle of solar system design we follow here at Polar Racking is that the site and ground will tell us what type of foundation/pile that best suits the conditions. For that reason, we have standardized our solar racking to fit with all foundation types and rely on our geotechnical reports for recommendations and not what we find convenient.
At the site in the U.S. Virgin Islands, our geotechnical report recommended ground screws because of their ability to handle tension, stress, and loading from the environment. Due to its large size and the threaded portion of the ground screw, it can resist loading forces much better than other foundation types. In the original project, the contractor used driven piles, which could not handle the high wind loads.
Other common failure points come from an inadequate thickness of the steel used in the racking and the small component design. When designing the project layout, we strategically used thicker steel racking while still able to keep our costs down. In addition, we selected the clamping and wiring design to maximize performance while still keeping the installation straightforward on-site.
Only half the battle is in the design – the other half is QA and QC during installation. PRI Engineering was tasked with ensuring the contractors installed the solar mounting system according to the engineering specifications. Issues with solar project performance commonly occur when contractors improperly install the foundations and racking. Thus, it’s extremely important to have a watchful eye on all foundation installations especially in environments prone to extreme weather because small mistakes during construction can lead to major issues in the future.
Proper design of a large-scale ground-mount solar system will not only prevent future costs through heavy repair but also can increase the expected performance of the system. Because of our redesign, the overall output of the system will increase from 4.2 MW to 5 MWs.