With their expansive roofs, bus maintenance facilities in major metropolitan areas represent significant opportunities for solar power. The Charlotte Area Transit System (CATS) in North Carolina now produces electricity on the roofs of its bus maintenance facility after a Sept. 2012 installation.
“The nine bus canopies comprise about an acre of land that is drenched by the sun, allowing them to produce clean, renewable energy,” said CATS manager of project development David Feltman.
The system designers, National Renewable Energy Corporation (NARENCO), a Charlotte-based engineering, procurement and construction contractor, proposed installing 126 BAA-compliant Sharp solar PV panels on each of the nine bus canopies for a total of 1,134 panels producing 331,000 kWh of electrical energy the first year.
Panels were to be laid flat on the south-facing roofs, which have a 3-degree pitch and are of standing seam metal construction.
“Ballasting was not an option on a roof of this type,” said Mark Caddell, Senior Project Manager and Systems Designer for NARENCO. “We needed a low-profile support system and also a way to easily manage the string wiring cables.”
The solution
The NARENCO team specified the Cablofil Delta Strut system from Legrand, the only solar panel support system that integrates solar panel framing and cable management into a single support. The welded-wire, open structure design clamps to the standing seam room, supports the PV panels, and incorporates the cable pathway close to the panels so cables are less likely to be damaged by wind and are shielded from direct sunlight. Also, there are no water or debris catch points that require future maintenance or cleaning. Delta Strut is lighter than standard channel framing and is tested to support solar panels in 150 mph winds.
“The panels are installed very close to each other so there’s no path to walk down. Delta Strut allowed us to do all the wiring prior to installing the panels,” said Caddell, who added that the standing seam mounting clamps worked well.
The Delta Strut system, which has passed electrical/bonding testing per UL 2703 allows simplified grounding.“Each row of Delta Strut only need to be bonded to the required equipment grounding conductor in one location. The splicing of the tray created a continuous bond the entire length that the NEC required,” said Keith Davis, NARENCO Vice President of Construction.
Delta Strut is designed for simplified, efficient installation. “We like the light weight and how it’s easy to lift a bundle to the roof and go from there. It means less manpower and rapid deployment,” said Caddell. “It’s a high-quality, well-made product that will probably outlast the panels and be available when the time comes to install new ones.”
— Solar Builder magazine
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