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Aluminum

The green metal

By Lynn Stanley

Fabricator uses aluminum for solar energy job

May 2012 - Concentrated photovoltaic solar power is an emerging technology that is quickly capturing market attention with its ability to multiply the sun's power and convert it into a cost-effective form of electricity. According to EnergyTrend, CPV works by using an optical component much like a lens or mirror to focus substantial amounts of sunlight onto solar cells made with photovoltaic material. The Green Economy Post predicts CPV’s ability to produce the same power from a much smaller area of solar cells will make the technology more cost effective than conventional PV. Manufacturers are developing innovative CPV systems for applications in the United States and other countries such as Italy, Australia and India. Fabricators are making smart material choices to support market growth with the necessary framework for these systems.

Material of choice
Aluminum was the material of choice when the Phoenix-based manufacturing facility of Hydro Aluminum North America was selected to provide a precision-extruded framing system for the largest concentrated photovoltaic solar facility in Latin America. The 500-kilowatt electric generation facility in Durango, Mexico, uses a Skyline Solar system made up of 184 by 14 arrays that contain parabolic mirrors to concentrate or focus sunlight onto crystalline silicon PV cells. The arrays are mounted on extruded aluminum space-frames that elevate the system off the ground and allow it to track the sun through its east-to-west arc.

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Hydro Aluminum provides drawn aluminum tubing, machining, contract manufacturing and metal sourcing to a wide range of customers. “The solar industry was a natural extension for us,” says Allan Bennett, vice president of solar market development for Hydro Aluminum. “Technology advances have helped push commercialization and market growth for both PV and CPV applications. As part of our latest project with Skyline Solar, we used our extrusion expertise to take mass out of their design for the framing system to reduce weight and cost.” Skyline Solar, Mountain View, Calif., manufactures integrated CPV systems that include industry-proven silicon cells, durable mirrors and single-axis tracking. The company holds 11 patents on its CPV architecture.

Cheaper, lighter
Steel is cheaper than aluminum on a per-pound basis, Bennett says. But aluminum, at one third the weight, if designed correctly can deliver the same strength characteristics as steel at a material cost that is comparable or lower when total cost of ownership is considered, he adds. Aluminum’s lighter weight means less labor is needed for assembly. Less weight also means more material can be loaded on a truck resulting in fewer greenhouse gas emissions.

“Aluminum is a very green material compared to steel,” says Bennett. “It’s very easy to design with, as well. You can take one extruded piece of aluminum and design multiple functions into it such as a screw channel or heat sink. With aluminum, you really are limited only by your imagination.”

Using its extensive library of alloys and extrusion expertise, Hydro Aluminum’s solar engineering specialists worked with Skyline’s team to analyze the design and optimize it for cost savings. “We were able to remove 40 percent of the structural material used in early frame prototypes,” says Bennett. “That reduced Skyline’s costs for raw materials, manufacturing and shipping.”

A long life
According to Bennett, extruded aluminum is corrosion-resistant and provides a high stiffness-to-weight ratio to resist wind, a feature that improved the Skyline system’s accuracy and robustness. “You don’t have to treat aluminum for outdoor applications,” Bennett says. For this type of project, steel would have to be galvanized, adding cost. Aluminum also offers a lower carbon footprint and is more recyclable.

Roughly 75 percent of primary aluminum in North America is produced using hydroelectric power, which is green in and of itself, says Bennett. “Seventy to 75 percent of the material used is post-industrial recycled content,” he adds. “When you combine these elements—the green power source used to produce it, the large percentage of aluminum that is recycled content—coupled with the fact that recycled aluminum only takes 5 percent of the energy required to produce primary aluminum, the material quickly becomes a relatively green and sustainable product.

In fact, since about 1880, a billion metric tons of aluminum has been produced,” he continues. “Approximately 74 percent of that material is still being used today due to its capacity to undergo the recycling process without the loss of performance properties.” In sunny climates like Mexico, CPV is the lowest-cost solar technology for medium and large-scale electricity-generating facilities. “It constitutes the fastest growing portion of the solar market and is a growing customer base for us as well,” says Bennett. The Durango CPV facility, approximately 550 miles north of Mexico City, will expand to 10 megawatts total capacity in the near future. MM

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