BIPV Roof Overcomes Challenges
By GINA R. JOHNSON
The mission: to fit 187 kilowatts (kW) of photovoltaics (PV) on a twice-reroofed, weight-limited structure, and to do it within a million dollar budget.
That was the challenge Dallas-based Horn brothers roofing and its supplier, Sheffield Metals International of Sheffield Village, Ohio, faced in 2009 in responding to a request for proposals from the Hopkins County Civic Center in Sulphur Springs, Texas.
Most bidders focused on putting crystalline panels on the civic center’s upper roof. But Horn Brothers and Sheffield Metals saw an opportunity to retrofit another roof area, over the facility’s stables, using a steel roof integrated with laminated thin-film panels.
The dilemma arose from a stimulus funding requirement that the system be installed on the structure of the civic center, according to CRW Associates’ Tom Glosup, a member of the civic center board and the project’s construction manager. In 2009, Hopkins County officials had received American Recovery and Reinvestment Act (ARRA) funding to make various upgrades, including reroofing the civic center. Later, the county applied for $827,000 in ARRA funding to install a 187-kW PV system to offset huge electric bills. That, plus $175,000 in rebates offered by local utility Oncor, gave the project an immediate payback. Unfortunately, not knowing at the time of the reroofing that solar might be a possibility, the county had chosen a roof with a 10-year lifespan — far less than the typical 25- or 30-year PV system life.
The building-integrated PV (BIPV) system enabled the civic center to comply with ARRA and stay within budget. It also reduced the total weight from 3 to 4 pounds per square foot for the roof, racking and crystalline system to about 2 pounds per square foot, said Jason Watts, vice president of business development for Sheffield Metals. The installation took place last winter.
Devil is in the Details
To achieve the ARRA-funded 187-kW capacity, the project team had to fill the entire stable roof with thin-film panels — more than 1,400 of them. “Watts [generated] per square foot is less on a thin-film amorphous [system], so we used just about every square foot of roof area we had,” said Watts. “We ended up with 189 kW.”
Metal roof panels averaging 150 feet (50 yards) long posed another challenge. The lengths of the panels made it tough to laminate them before hoisting them to the roof, so the team added the solar laminates on the roof. “As the roof panel was put down, they were following behind laminating solar panels,” Watts said.
A moment of panic came when the team realized that, once Texas’ scorching heat was factored in, the 310- to 500-volt transformers the design called for were mismatched to the two 95-kW central inverters. “In a perfect world that would be fine, but when they get their hot days, we were going to drop down to 300 [volts], somewhere around there,” according to Watts.
“I don’t know that there’s a way to put a dollar value to what the civic center brings to our county and the counties around,” Glosup said.
“Thank goodness we were dealing with Solectria. They said, ‘Don’t worry about it, we’ll just put another transformer in that will go down to 300 and we won’t have a problem.’” He added, “The last thing I wanted was Hopkins county calling me up and saying, ‘Hey, it’s 100 degrees and sunny, and we’re not getting any power.’”
Once the roof system was installed, systems integrator CAM Solar, based in San Antonio, arrived on the scene. Their team discovered that the roofers had laid the panels symmetrically, not realizing that the integrators needed to string the panels so as to match total voltage with that of each inverter. “We ended up sticking a few extra laminates on one end to match it all together voltage-wise, and we had to kind of finesse the conduit run to the combiners to some degree,” said CAM Solar President Brian Cullen. “It really wasn’t that big a deal.”
Region’s Economic Driver Gets Efficient
The location brought a few more tests: 3 inches of ice on the roof during the region’s unusually bitter winter, and the unique risks of clunking across a metal roof over valuable livestock. one weekend during a big stock show at the civic center, the facilities manager asked CAM Solar to vacate the roof. “He says, ‘You’re scaring all the cows below!’” Cullen recalled, laughing. “So literally, we had to pack up our guys.”
After all, the facility is serious business to those showing their animals, said Cullen. “This is their livelihood.”
Glosup concurred. “I don’t know that there’s a way to put a dollar value to what the civic center brings to our county and the counties around,” he said. “The cheaper you can run that, the better it is for the residents of Hopkins County.” The Civic Center has installed a new air conditioner and taken other conservation steps as well.
Sheffield metals estimates the system will produce 293 megawatt-hours annually, saving the Civic Center tens of thousands of dollars per year in electricity bills.
Gina R. Johnson (email@example.com) is SOLAR TODAY’s editor/associate publisher.
Pv System Highlights
Hopkins County Civic Center,
Sulphur Springs, Texas
Average Solar Resource: 5.33 kilowatt-hours/square meter/day
Average High/Record Low Temps: 54°F–96°F (12°C-36°C)/minus 4°F (minus 20°C)
Latitude: 31.1 degrees north
General Contractor: Horn Brothers Roofing
System Designer, Supplier: Sheffield Metals International
Systems Integrator: CAM Solar
Array Capacity: 189 kilowatts
Annual AC Production: 292 megawatt-hours
Panels: 77 68-watt (PVL-68) and 1,386 136-watt (PVL-136) thin-film laminates from Uni-Solar
Inverters: Two Solectria Renewables PVI 95 kW−480 VAC inverters
Array: 63 strings of Uni-Solar PVL-136s
Array Combiners: Solectria STRCOM 21 circuit
System Installation: Thin-film laminates on a retrofit standing-seam metal roof.
4.76° tilt, 180° azimuth
System Monitoring: Solectria SolrenView
Installation Time Frame: Three weeks in January–February 2011
Cost and Incentives
BIPV system with uni-solar thin-film laminates: $1.027 million
ARRA grant: ($827,000)
Oncor utility rebates: ($175,000)
Total cost after incentives: $0
by SOLAR TODAY
SOLAR TODAY is published by the American Solar Energy Society. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We have been advancing solar energy for 60 years.