White Roof Coatings Boost Solar Power

By Charles W. Thurston, Contributing Editor | September 14, 2011

Most of the interest in white roofs comes from the heat reflection of the surface, which reduces energy consumption for cooling.

Manufacturers of white roof coatings and emulsions have an emerging niche demand from photovoltaic solar power systems that are designed to absorb the albedo, or reflected light from a flat or low angle roof surface. White sheet materials generally offer reflectivity efficiency in the range of 80 percent, but some liquid formulators are creating products with 90 percent or higher reflectivity efficiency, which can boost the energy production of attuned solar systems by 20 percent to 30 percent over standard flat panels, industry sources say.

While white sheet manufacturers including Carlisle, Firestone, GAF and Johns Manville now control the lion’s share of the white roofing material market. Among materials used for white sheets are vinyl, EPDM, and the most rapidly growing, TPO or thermoplastic polyolefin.

TPO consists of “polymer/filler blends usually consisting of some fraction of PP (polypropylene), PE (polyethylene), BCPP (block copolymer polypropylene), rubber, and a reinforcing filler,” according to Wikipedia. TPO now is used in more than a third of roofing installations, according to one industry estimate.

The liquid products will find greater demand in recoating black or white roofs, since the liquid is less expensive than the sheets, says Jonathan Ursini, the marketing manager for DuROCK Alfacing International, of Woodbridge, Ontario, Canada. His company produces Tio-Coat, which is a titanium dioxide-based product that includes some 40 ingredients, including Dow’s Rhoplex EC-3100, an all-acrylic polymer designed primarily for use in pigmented elastomeric basecoats. Tio-Coat provides 89 percent reflectivity efficiency. “We took five years to formulate the product, and wanted to raise the performance bar a bit,” he said. The coating can extend the life of a sheet material by an estimated 10 years, he noted. Tio-Coat can be applied to asphalt, concrete, foam or metal.

The Cool Roof Rating Council, of Oakland, Calif., maintains a technical database of material properties on 1,000 products, including reflectivity, and has rated materials as high as 94 percent, according to Jessica Clark, a marketing officer for the council. The U.S. Department of Energy’s Energy Star rating for roofing material reflectivity requires 65 percent efficiency new, with a 50 percent performance for worn materials. Most of the interest in white roofs comes from the heat reflection of the surface, which reduces energy consumption for cooling.

At least two solar module manufacturers now produce solar modules that can absorb reflected light. Sanyo North America, based in San Diego, Calif., sells a double-sided flat solar panel, the HIT Double, and Solyndra makes a cylindrical solar module, which absorbs across 360 degrees of reflection. Solyndra’s cylinders yield 20 percent more power than a standard upward facing flat solar panel, according to David Miller, a spokesperson for the Fremont, Calif.-based company. The Sanyo panels increase the solar power yield by 30 percent, according to company information sheets.

The market for white roofs in California has been boosted by a requirement that new commercial roofing be white, under Title 24 codes. Because Ontario has a 60 percent local content requirement for solar systems, Sanyo and Solyndra solar modules are not likely to see great gains in the province. Accordingly, DuROCK plans to open a California office within 60 days, and has already had its product tested with Solyndra. “We laude the foresight of California in requiring white roofs,” Ursini said.

In other news Schneider Electric announced it had secured a contract with the United States Coast Guard (USCG) in Puerto Rico to install 2.89 megawatts of solar panels on renovated Coast Guard rooftops over a 13-month period.

The company says the rooftop solar rollout, part of its comprehensive $50 million energy savings performance contract (ESPC) with the Coast Guard, will see electricity production of more than four million kilowatt-hours per year.

Combined with new “cool roofs”, the solar power systems will slash the annual cooling load of the buildings by 3.9 billion British Thermal Units, resulting in an overall reduction of utility-purchased electricity by an estimated 40 percent.

The cool roof measures included insulation, reflectivity and improved drainage, with energy and operational savings offsetting the costs of implementation.  

“Reducing the Coast Guard’s energy consumption and developing renewable energy solutions in Puerto Rico not only helps the Coast Guard meet federal mandates, reduce green house gas emissions and stabilize energy costs, but it also can help create green collar jobs in Puerto Rico. This project will have a significant impact on the industry there,” said Capt. John Hickey, commanding officer of Coast Guard Shore Maintenance Command in Seattle.

In new technology development coatings manufacturer EPOX-Z Corp. recently introduced EPOX-Z NRG, a two-part cool roof coating designed for use with PV installations on flat commercial roofs. According to the company, the material provides a life span that parallels the typical length of a solar power purchase agreement.

The solventless, odorless coating contains no volatile organic compounds (VOCs) and can mitigate the damaging effects of ponding water on flat commercial roof surfaces, EPOX-Z said.
The company offers a partner incentive program that allows approved solar companies to earn an instant rebate if they partner with EPOX-Z. The solar company can either retain the rebate or pass the savings through to the customer.

What is a Cool Roof?
A cool roof reflects and emits the sun's heat back to the sky instead of transferring it to the building below. "Coolness" is measured by two properties: solar reflectance and thermal emittance. Both properties are measured from 0 to 1 and the higher the value, the "cooler" the roof.

Benefits of cool roofs include:

• Energy savings and global warming mitigation;
• Reduction in urban heat island effect and smog;
• Improved occupant comfort; and
• Comply with codes and green building programs.

For more information visit The Cool Roof Rating Council (CRRC) on the web at www.coolroofs.org.