Cutting-Edge Technology Minimizes Project Footprint
By Rick Jones, Ph.D., C.P.E.
The Fayetteville Public Works Commission (PWC), which provides electric service to more than 87,000 customers and is the largest public power provider in North Carolina, recently completed the state’s first municipal community solar and energy storage farm. The installation provides enough energy to support the equivalent of 100 homes and is available to Fayetteville PWC customers as a shared renewable energy option.
Providing Customers with a Renewable Resource
While solar is becoming an increasingly appealing option to environmentally conscious homeowners, many residences are not suitable for the installation of panels. Older roofs, shaded roofs, or those lacking a south-facing orientation may be barriers to installation, as well as up-front costs and ongoing maintenance requirements. Many customers also rent their homes, preventing them from installing solar panels. The Fayetteville PWC Community Solar Program is a large-scale, ground-mount solar array that enables residents to benefit from municipal solar through a monthly subscription service. Eligible customers may subscribe to a maximum of five panels for a period of up to 25 years.
The Fayetteville PWC selected Dewberry as general contractor for the turnkey, design-build project. The system consists of a nominal one megawatt alternating current (MWAC) per 1.2 megawatt direct current (MWDC) solar photovoltaic array, with a nominal 500 kilowatt direct current (kWDC) lithium-ion battery bank along with wiring, inverters, and controls. The use of string inverters, which convert the 12-volt DC power produced by the solar array into useable 120-volt AC power, together with a mini-battery storage system, allowed for a significantly reduced project footprint
over standard, utility-scale inverter systems.
The string inverters are housed in two-foot by two-foot containers placed every three rows among the panels, with the entire array spanning approximately six acres. The battery storage system and controls are sited on a concrete pad measuring approximately 30 feet by 15 feet, and the cabling and conduits are run underground.
The ground-mounted array consists of 3,384 Tallmax 72-cell multicrystalline 330-watt modules with a single-axis tracking system that features a two-hour battery discharge capacity duration. Each solar panel produces an average of 39 kilowatt hours per month, or close to 470 kilowatt hours per year, subject to weather variations and seasonal/daytime variations in the angle of the sun. The combination of the solar array with the battery system enables the Fayetteville PWC to discharge battery power during peak demand, when buying wholesale power from Duke Power is the most expensive. The lithium-ion battery will store 1,120 kilowatt hours of electricity.
The Fayetteville PWC estimates that the average residential customer uses 1017 kilowatt hours of electricity each month, with the potential for five solar panels to produce an average of 196 kilowatt hours per month, or approximately 19 percent of consumed energy. The energy generated from the panels is delivered directly to the grid and credited to subscribing customers.
Dewberry also assisted the Fayetteville PWC with establishing a maintenance program, primarily focused on cleaning the panels twice a year. With much of the equipment protected in waterproof conduit underground, extending from the inverters to the batteries to the transformer, the system is designed to be low-maintenance and resilient from extreme weather.
A Model for Community Solar Installations
The Fayetteville PWC collaborated with the U.S. Department of Energy’s Community Solar for the Southeast project, led locally by the North Carolina Clean Energy Technology Center (NCCETC) and several partners to assist public power utilities in identifying solutions to provide community solar systems. NCCETC provided Fayetteville PWC with a technical and economic analysis to gauge viability, costs, and project value, and assisted with the evaluation of program options.
Although the Dewberry team was challenged by adverse weather including two hurricanes, the project was completed in 11 months. The Fayetteville PWC Community Solar project now serves as a pilot for other municipal and cooperative electric utilities to develop similar installations. “This is about the future. It’s long-term sustainability,” stated David Trego, Fayetteville PWC CEO and general manager, at the ribbon-cutting. “While our current customers will enjoy the benefits of this, it is our children who will truly have the benefit of a project like this in the long run.”
Rick Jones is a construction manager in the Raleigh office of Dewberry.