Down a quiet gravel road in a small community in the piedmont of North Carolina, Joe Gamble and Suzanne Thompson’s house often loses utility power during too-common hurricanes and ice storms. Their first priority was PV-powered battery backup for the well pump, but they also wanted to power as much of their residence as possible with renewable energy.
DPW Solar provided the engineered rack system, which Honey Electric Solar installed on the steep slope.
Their home—a geodesic dome—was particularly problematic for a roof-mounted PV system. The multiple azimuths and tilt angles of the curved dome would have meant installing modules at wildly different orientations or with a complicated rack attachment system—not usually a wise PV design decision (although microinverters or module maximizers might help alleviate the energy production aspects of this problem).
Footers were reinforced with rebar and inspected prior to pouring concrete.
The siting focus turned to a field behind the house. But the field had its own issues: it was covered with brush, included a perilously steep western slope, and was bordered to the north by a utility right-of-way and on the south side by a row of evergreen trees.
Poured concrete piers provide solid footing for mounts and BOS components.
Type of Mount
For PV arrays situated in fields like Joe and Suzanne’s, there are two choices—pole mount or ground mount. Pole-mounted PV arrays sit atop a heavy, steel pole (usually 6 or 8 inches in diameter) that is anchored in yards of concrete. Ground-mounted racks have multiple smaller supports that secure the array, and usually sit closer to the ground. The slope of their field was too steep for concrete trucks or other heavy equipment, ruling out the pole-mounted solution.
Honey Electric Solar designed and installed the 2.8 kW PV system with two, side-by-side ground-mounted DPW Solar racks. Each rack accommodates eight, 180 W Evergreen PV modules that power an OutBack battery backup, grid-tied inverter. The Gamble array was limited to four modules in a series string, due to the module voltage, temperature extremes, and charge controller voltage window. If the strings had been limited to three modules instead of four, it would have meant splitting a string across the two racks.
Cross-bracing keeps the plane of the modules from flexing under wind or snow loads.