CLIENT: BMR Energy
PROJECT DESCRIPTION:
PRI Engineering provided geotechnical investigation, foundation design, and construction quality control for the rebuild of the Donoe Solar Farm — a 6.44 MWdc ground-mount facility on St. Thomas, U.S. Virgin Islands, developed by BMR Energy (a Virgin Group company). The original facility, built in 2015, was destroyed by Hurricanes Irma and Maria in 2017 along with over 80% of the island’s power infrastructure. PRI Engineering was engaged to ensure the rebuilt system was structurally engineered to withstand Category 5 hurricane wind loads for the full 25-year project life.
CHALLENGES:
The Donoe site presented a convergence of demanding conditions rarely encountered on a single project:
- Significant slope and terrain variability — elevation changes affected load transfer through the racking system and introduced differential behavior across the site
- Heterogeneous subsurface conditions — soil types, rock depths, and bearing capacities shifted substantially across short horizontal distances, precluding a uniform foundation approach
- Aggressive coastal environment — proximity to the ocean elevated corrosion risk and lateral force sensitivity
- Extreme wind loading — the racking system was designed for 180 mph wind loads, well beyond standard North American requirements
- Prior foundation failure — the original screw pile system had failed under hurricane loading, requiring forensic analysis before any design work could begin
APPROACH:
PRI Engineering conducted a comprehensive, boots-on-the-ground geotechnical investigation across the full project footprint in October 2020, travelling to St. Thomas alongside the racking contractor, Polar Racking. Rather than applying a standardized solution, the team treated subsurface variability as a design input — mapping conditions zone by zone to determine where standard approaches were appropriate and where site-specific solutions were required.
A key recommendation was the move from screw piles to driven piles, supported by a full pile pull-out test program that characterized soil conditions and determined the required pile size and embedment depth — a minimum of six feet — validated by testing rather than generic design tables. This foundation specification was explicitly matched to the 180 mph structural demand of the racking system above it.
PRI Engineering also drew on an unconventional source of expertise: years of designing solar foundations for frost-heave conditions in northern Canadian markets. The engineering insight — that frost uplift and wind uplift are conceptually analogous load problems — translated directly to the Caribbean context, informing a foundation system purpose-built to resist the uplift forces that destroyed the original facility.
Construction quality control was embedded throughout installation, with PRI Engineering personnel on-site in St. Thomas to monitor pile depths, track installation performance, and adapt the design in real time where subsurface conditions diverged from investigation findings.
OUTCOME:
The Donoe Solar Farm came back online in 2022, generating approximately 10,400 MWh of clean energy annually for the Virgin Islands Water and Power Authority under a 25-year power purchase agreement. The project reduces the island’s greenhouse gas emissions by an estimated 9,700 metric tonnes of CO₂ equivalent per year. By designing foundations to meet the terrain on its own terms — rather than forcing a standard system onto a non-standard site — PRI Engineering delivered a facility built to outlast Atlantic hurricane seasons for the full duration of its operational life.
