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The Science Behind Thin-Film Solar Technology

By Chris Grethlein

 

Corrosion-resistant roofs with integrated photovoltaic cells take advantage of two emerging technologies to provide both sustainable roofing and electric power.

All solar cells require a light-absorbing material contained within the cell structure to absorb photons, which subsequently generates electrons via the photovoltaic effect. The materials used in solar cells preferentially absorb the wavelengths of solar light that reach the earth's surface. Thin-film solar cells are available as appliqués that are bonded to the corrosion-resistant metal roofing panels prior to mounting the integrated photovoltaic roof panels in place.

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New Army Roof Fights Corrosion and Generates Power

Even at a distance, the severe weathering of this roof at Kilauea Military Camp, Hawaii, is evident. Photo courtesy of U.S. Army Corps of Engineers ERDC-CERL.

The U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC/CERL) has implemented a novel multifunctional solution to address two major facilities-related challenges at once—preventing corrosion and reducing energy consumption. In a pilot program at Kilauea Military Camp in Hawaii, ERDC/CERL targeted a 5,500-square-foot vehicle storage building for refurbishment, which had a highly corroded corrugated metal roof. The refurbishment used a system that incorporates a standing seam metal roof having a high-performance coating and photovoltaic cells based on thin-film solar technology.

Hawaii is a very corrosive environment for military infrastructure. The physical structures of the Kilauea Military Camp are subject to a harsh environment of alternating rainstorms and searing, radiant sunlight—conditions typical of Hawaii's many unique microclimates. Many of the buildings at the camp experience severe corrosion problems as a direct result of the rain and associated humidity, exacerbated by the heat and ultraviolet exposure from the sun. As expected, corrosion manifests itself most harshly on the metal roofs of these buildings, which are used to protect occupants, mission-essential materiel, spare parts, and maintenance equipment from the tropical rains and the hot, humid environment.

Corrosion isn't the only pressing problem for military facilities. Following recent changes in DoD policies, all military installations are now directed to reduce their reliance on conventionally supplied electric power, particularly when it is generated from fossil fuels. To minimize pollution from fossil fuel power plant emissions, the state of Hawaii is encouraging greater use of cheap alternative sources of electric power, preferably from renewable sources.

The integrated roof panels are first assembled on the ground, and then raised into place as single units. Photo courtesy of ERDC-CERL.

Following Army policy and Hawaii state directives, Kilauea Military Camp is seeking alternative energy approaches that are environmentally sustainable. To demonstrate such technologies, ERDC/CERL and the Kilauea Military Camp Public Works office have integrated photovoltaic cells with a new standing seam metal roof on building 84. (See The Science Behind Thin-Film Solar Technology.) This technology uses a free and plentiful energy source, the sun, with little environmental impact. Moreover, the photovoltaic components are thin-filmed laminates—flat modules that are adhered to the metal roof-anel surface. They do not require racks for mounting, as with conventional photovoltaic technology.

Thin-film solar cell technology has been used in the commercial sector for some time, but this is one of the first military applications of the technology that is being monitored for its energy output as well as its impact on corrosion resistance when integrated with metal roofing. According to Dave Bailey, ERDC/CERL project manager, "While the power produced by these integrated roof systems is dependent on the scale of application, the product's manufacturer claims power ratings for such solar modules ranging from 10 to 100 watts at peak demand hours. Kilauea Military Camp also expects to realize significant improvements in the service life of the roof by using standing seam metal roofing with a high-performance coating."

Under nominal conditions, the photovoltaic cells could offset up to 25 percent of the load for the building, previously supplied through the commercial grid, Bailey noted. "At such times, the excess electricity will be distributed back to the local Kilauea Military Camp grid."

The results of this pilot project will be watched carefully, as photovoltaic systems could potentially save a substantial amount of energy used over the lifetime of the building, Bailey noted. Over the next ten years, Kilauea Military Camp is scheduled to undergo major upgrades to the bulk of its facilities. If this initial pilot effort yields sufficiently positive results, it could lead to many additional applications of this corrosion resistant/photovoltaic roof system. The other services and the Coast Guard are also interested in seeing the outcome of this project, since many of their installations include buildings with similar roof-deterioration problems. They also share the same need for environmentally sustainable electric power.

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