Client RES System 3, Inc. / AES Distributed Energy
Scope 5 MW on 32 acres

USVI Solar 1

Project Details

Voted Ground-Mount Project of the Year in 2015 by Solar Builder Magazine, this 5 MW PV solar plant is perched high on a ridge of St. Thomas, a U.S. Virgin Island, and provides reliable electricity for well over 500 homes.

Westwood’s Role

  • Civil and Electrical Engineering
  • Hydrology and Drainage Design
  • Topographic Surveying
  • Aerial Mapping
  • PV Production Modeling and Array Design
  • Construction Services


St. Thomas is home to an award-winning 5-MW PV solar plant that is expected to generate approximately 7.9 million kWh of electricity annually. This renewable energy system is much needed in the area and is expected to reduce electric costs by fifty percent. The island’s steep terrain, fast growing local vegetation, and seasonal threat of hurricanes presented unique challenges to the design and schedule.

Overcoming Obstacles

The 32-acre plot varied substantially in topography, which challenged the design and construction of the fixed-tilt solar rack arrays. Initial plans were designed using a 2007 USACE aerial map. The accuracy of the map was limited due to the existence of vegetation present when the map was created. Once the site was cleared, Westwood’s own aerial mapping team gathered and processed new data to accurately reflect the existing ground features. Westwood’s enginee team redesigned the solar array to work effectively with the existing terrain.

Due to the site’s slopes ranging from 20 to 50 degrees and a problematic east-to-west curvature that could limit solar efficiency, the team used Helios 3D software to optimize the placement of each module. This software significantly enhanced Westwood’s ability to design the highest energy-producing system possible for the site.

Once the design was complete, it took experienced survey crews to perform construction staking. Slopes, cliffs, and rocky ground required hands-on, traditional survey tools to accurately mark the location for each pile. Westwood provided constant, day-to-day support to the contractor throughout construction to ensure the plan was built correctly and issues were addressed quickly.

Vegetation and Erosion Control

The site required clearing of vegetation to begin the project. Much of the site was comprised of the non-native, noxious Tan-Tan tree, which grows up 12 inches per month. Its rapid growth rate would quickly impact the solar arrays if not controlled both during and after construction. The trees will require on-going clearing because its seeds cannot be eradicated.

Given the climate and extreme topography of the project site, erosion became a major concern after the site was cleared of vegetation. Hydro-seeding was utilized at each stage of construction to ensure the topography would remain intact and erosion would be minimized.

Also, the project site presented two unique water-flow challenges. During and after construction, Westwood was required to restrict water and sediment flow to the neighboring property at a rate at or below current rates. In addition, the team discovered dangerous erosion threatening a main road connecting the east and west sides of the island at the site. Westwood’s solution was to design a system of energy-dissipating rock dams, ditches and culverts leading to detention basins near the bottom of the site. The basins utilize weirs to monitor and restrict the escape of water from the site at a pre-determined flow rate. This solution successfully resolved both of the water flow challenges.