Advanced solar roof racking solutions mitigate PV system cost

By Matthew A. Thompson, Ph.D., Director of the Principal Solar Institute, and James R. Kirby, AIA, Vice President of Sustainability, Center for Environmental Innovation in Roofing

Matthew A. Thompson, Ph.D., Director of the Principal Solar Institute

Roofing System Success

To successfully address these issues, the roofing system should be designed and installed to serve as a permanent platform for the continuous operation, service and maintenance of the PV system. In terms of investment, the roofing system is especially critical. Not only must the remaining service life of the existing roof system be adequate to meet or exceed the investment horizon of the PV system, but there should be a detailed review of the compatibility of the existing roof to accommodate the PV system both initially as well as during ongoing operations. 

Advances in affixing the PV system to the roof using state-of-the-art roof racking systems not only address the above mentioned challenges, but also drive down the total costs of PV installation.

Roof Racking Issues

Residential. Roofs that are steep-slope (standard for most residential homes) present certain issues for PV module racking that pose no problems for commercial installations, such as overall appearance of roof-mounted PV modules. Several manufacturers now offer solar shingles that greatly reduce the negative aesthetic impact of PV solar panels. However, most residential PV systems are elevated above the roof, but still retain a low-profile appearance. The racking structures in these designs use stand-offs and fasteners that penetrate the roof to keep the assembly from sliding off, and provide mechanical stability in high winds. The integrity of the penetration points is crucial, as each must be properly sealed to prevent water leaks. Additionally, most residential roofs have surfaces facing different directions, which can impact area utilization for electrical generation.

Commercial. Roofs that are low-slope (standard for commercial buildings) are geometrically simpler, walkable, and therefore lend themselves to ballasted PV module technology.  A ballasted system relies on the weight of the ballasted and racking structures to hold the PV modules in place.  A nearly horizontal roof presents good exposure to mid-day sunshine when daily solar production reaches its peak.

Materials. An issue common to all rooftop PV systems is the durability of the materials constantly exposed to the sun and weather. Fortunately, recent material innovations increase service life.  The newest generation of PV systems entails Fibrex, a lightweight composite material with excellent weathering characteristics and insect resistance. Such materials do not corrode or degrade quickly and can provide a serviceable lifetime consistent with the PV cells.

Labor Costs. The cost of PV solar panels has declined considerably, and now represents approximately 40 percent of the total system cost, down from 80 percent just a few years ago. Economy of scale has similarly led to cost reductions in inverters and other system components. Despite the cost reduction of PV modules, and other "Balance of System" items, widespread adoption in the U.S. has been stymied, in part, by issues related to roof racking products that involve complex, labor-intensive assembly and installation procedures requiring skilled labor and special tools.  Labor costs for solar roof projects involve installation, as well as design and engineering. Therefore, as component costs of PV systems decrease, labor has become a significant cost driver.  

Roof Racking Solutions
A number of state-of-the-art roof racking products have emerged to address all of the above issues. These new products for low-slope rooftops, typically encountered in commercial and industrial buildings, employ completely modular solar panel systems.  Such systems do not require roof penetration for stability, but rely solely on the ballast and weight of an interlocking substructure that anchors the PV modules and require few tools for installation. The PV modules have integrated electrical connectors that further reduce skilled labor costs.  The negative and positive leads snap together, which eliminates the need of individual grounding connections and can be done in a matter of seconds.  The modular design further reduces total installation time because components arrive to the job site on a pallet, which can be craned or fork-lifted onto the roof.

In addition, some of the most advanced solar roofing systems on the market today offer features such as a range of sizes, shapes, and colors to blend in or enhance the aesthetics of the roof.

Given the level of innovation in the solar roofing industry, the potential benefits have never been greater. Solar energy is a low-risk investment that increases property value, reduces dependence on the electricity grid and saves on utility bills.

About the Authors
Matthew A. Thompson, Ph. D., is a scientist with 23 years experience in semiconductor process development and yield enhancement at Motorola and Freescale Semiconductor, and is Director of the Principal Solar Institute, www.principalsolarinstitute.com

James R. Kirby, AIA, Vice President of Sustainability, Center for Environmental Innovation in Roofing, Washington, D.C., serves as co-liaison for the Center's PV taskforce, represents the roofing industry at sustainability-focused events, and authors and presents sustainability-based technical information to the PV and roofing industries within the U.S. and internationally.