CR Soprema1
When the roof of its headquarters needed to be replaced, Valley National Bank decided to incorporate solar energy. Pfister Energy installed an integrated photovoltaic roof system, which combines a Soprema modified bitumen roof with Uni-Solar photovoltaic film. (Photos courtesy of Soprema/Pfister Energy.)
Saving energy is important, but renewables "it’s a much bigger step," says Pfisterer. "We’re offsetting a significant amount of pollution emissions. Green roofs and cool roofs save energy, but it’s another thing entirely to generate clean energy on site."
Headquartered in Paterson, N.J., Pfister Energy designs, installs and maintains photovoltaic (PV) systems. Pfisterer believes that rising energy costs, growing energy consumption and limited supplies of fossil fuels will send the number of solar applications skyrocketing in the near future. The fact that the launching pad for most solar systems is located on the roof brings in another set of variables to consider.
Understanding how a PV system interacts with the roof is essential. Dissimilar materials have different rates of thermal expansion and contraction, so differential movement of the PV and roofing materials has to be taken into account. In addition, some systems may necessitate multiple penetrations that could potentially cause problems. These factors need to be fully understood and properly engineered in order to avoid premature roofing system failure and/or de-lamination of the PV modules. Other important considerations include whether the solar panels would void an existing roof warranty or make it harder to conduct roof repairs in the event of a leak.
"The key question is: ‘How is the power plant going to be installed on the roof?’" says Pfisterer. "And to answer that question, you’ve got to know the roof."
The optimal answer, in Pfister Energy’s view, is a fully integrated system, with the PV panels tied in as an integral element of the roof system, installed by one contractor and covered by one warranty. Sharing that vision are Soprema USA, a roofing and waterproofing materials manufacturer headquartered in Wadsworth, Ohio, and Uni-Solar, a manufacturer of PV thin-film in Auburn Hills, Mich. Working together in conjunction with Pfister Energy, the companies are able to offer and install a system that combines a modified bitumen roof and solar technology with the panels and the roof covered under a single-source 20-year warranty.
The solar panels are carefully set in place with a two-part cold adhesive, and only one penetration is required for the solar power system.
Working Together
"I first got involved in photovoltaics five years ago," Pfisterer recalls. "There were a lot of manufacturers of PV systems out there, but the installations often caused problems with the existing roof."The goal was to find a solar product that could be integrated into a roof system and installed along with the roof. Uni-Solar had a product that seemed like a perfect fit.
"With Uni-Solar, the thin-film technology lent itself to commercial roofing for several reasons," says Pfisterer. "It was flexible, less brittle, and could be easily integrated with commercial roofing systems."\
The other necessary component was a roof system manufacturer to participate in the venture. "When you look at photovoltaics, with a lifetime of 25 to 30 years, there are very few roofs that will take you there," says Pfisterer. "Even with some systems warranted for 20 years, you can see some problems crop up at the end of the warranty. And the solar panels can make it difficult to do even minor repairs."
"Soprema’s two-ply SBS modified bitumen system had the longevity we were looking for," he continues. "We felt it was important to take into account the life expectancy of the two systems and marry them together."
The roof system is carefully engineered on a CAD plan, and each one of the cap sheets is laid out so that the solar panels never cover a seam or an end lap.
The System
The backbone of the integrated system is a two-ply styrene butadiene styrene (SBS) modified bitumen roof system manufactured by Soprema. The SBS system can be installed in a variety of ways: torch applied, heat welded, with a cold-applied two-part adhesive or with fasteners. A two-part cold epoxy adhesive is used to adhere the solar panels directly onto the roof.According Charles Hallenbeck, regional manager for Soprema, the roof system is carefully engineered on a CAD plan, and each one of the cap sheets is laid out with the optimum solar panel design in mind. That way, the solar panels never cover a seam or an end lap.
"By integrating the PV system with the roof system, the owner gets the benefits of long-term securement and ease of maintenance, coupled with long-lasting water-tightness in a roof with far fewer roof penetrations than rigid glass systems," says Hallenbeck. "The PV system can also be easily fitted to any rooftop configuration by virtue of the panel sizes and the flexibility of the panel itself. Their toughness and durability make them impervious to dynamic puncture insults from nature (such as hail) and from human activity (such as dropped tools). The inherent long-term durability of the panel itself coupled with a PV system with minimal components translates into a system that is as permanent as any being marketed on the planet."
"The SBS membrane system technology we have developed will last, we believe, in excess of 50 years," states Hallenbeck, noting that the company has SBS projects that are still in fine working order 35 years after they were installed. "The PV technology should normally last a minimum of 30 years with little or no maintenance. This means that after the integrated system produces or generates a positive cash flow, the owner should normally enjoy a positive cash flow for at least 25 years."
He stresses that almost all system evaluations indicate a positive return on investment within 10 years of initial installation, if not sooner. "Even if the owner elects to sell the building, they enjoy the advantage of having an income-producing PV system on the roof," he says. "As one of our owners observed, ‘It’s like having an oil-producing well in the backyard.’ "
Minimizing Problems
Penetrations are a common source of roof problems, and Pfisterer points out that the system is designed to keep them to a minimum. The panels are attached by cold adhesive "no pitch pans, no ballast," he says. "The solar panels become a part of the roof system. There is only need for one penetration: a conduit line to the power into the building, and it could be integrated in an existing pitch pan. This minimizes the potential for problems."Some PV panels don’t necessarily move as much as the roof surface will, Pfisterer points out, which is another problem that could lead to damage. "The differential movement of the products has to be taken into account," he says. "The two-ply SBS closely matches the movement of the solar panels."
When it comes to the performance and benefits of the system, Pfisterer and Hallenbeck aren’t confined to speaking of hypothetical cases. They simply point to the installation at the headquarters of Valley National Bank in Wayne, N.J., which has been in operation since July 2005. When the existing roof needed replacement, bank management wanted to incorporate solar energy, and Pfister was asked to install the integrated PV panel roof system.
The 22,425-square-foot project features a base ply of Sopralene Flam 180 and a cap ply of Sopralene Flam 180 FR CR White over 1/2-inch DensDeck and the existing insulation and steel deck. The solar panels were then carefully set in place with the cold adhesive, and soon after the system was generating power and earning New Jersey Renewable Energy Certificates. The system features a data acquisition system that documents information on payback.
Maximizing Benefits
"In a nutshell, the quality of the energy payback is typically governed by the local utility, and/or the applicable state or federal incentive in place at the time of purchase," states Hallenbeck. "If, for example, the local electric utility has an incentive in place with either a capital expenditure rebate or special buyback rate, the payback can be as little as three years. If no incentive exists, the payback may be as long as 10 years.""The one factor that is sometimes lost is that everyone’s local utility is required, by federal law, to buy back kilowatts generated at ‘the local wholesale rate,’" Hallenbeck says. "This means that the wholesale rate is highly volatile from place to place. In Connecticut, for example, the wholesale rate is high due to the concentration of nuclear power generation. In the Northwest, the abundance of cheap hydro generation requires a longer payback."
"Regardless of the payback, local integrated PV generation raises the collective consciousness of the building occupants," he says. "This translates to people being very aware of how they use energy and almost always results in an overall reduction of wasteful energy use. If the integrated PV installation has an easy-to-use data acquisition system in a common area such as a lobby, the PV production becomes more than a novelty. A percentage of building occupants will actually start watching the PV generation, much like watching the weather, and this will directly effect the mindset of efficient energy use to even a greater degree."
Another factor to consider is the country’s infrastructure, notes Pfisterer, especially the antiquated electrical grid. "In the summer, it’s the grid that’s the problem," he states. "How do you fix this problem? You can economize, minimize power use, or generate power. Solar is generating power at peak times for the grid. We can spend hundreds of millions or billions on upgrading the infrastructure, or we can offset the strain by generating on-site power and using energy efficiently."
