Solar Decathlon showcases cylindrical PV panels

Oct. 15, 2009
WASHINGTON, DC--Pennsylvania State University (Penn State; State College, PA) is competing in the October 9–16 Solar Decathlon, a Department of Energy-sponsored competition among 20 colleges and universities to create the best solar-powered home, with homes to be displayed on the National Mall.

WASHINGTON, DC--Pennsylvania State University (Penn State; State College, PA) is competing in the October 9–16 Solar Decathlon, a Department of Energy-sponsored competition among 20 colleges and universities to create the best solar-powered home, with homes to be displayed on the National Mall (see “What we’ve done at Penn State goes beyond the Solar Decathlon,” says Thomas Rauch, Penn State student and Solar Decathlon team member and industrial relations liaison. “We have developed a low-cost practical home that offers a sustainable model for the future.”

Penn State is hoping that its unique incorporation of Solyndra (Fremont, CA) cylindrical photovoltaic (PV) panels on Natural Fusion (see, the 800-square-foot house the team is constructing for the competition, makes a statement much bigger than just the opportunity to win a contest. “We need to redefine the concept that sustainability is sacrifice,” says Rauch. “Natural Fusion is not just a concept house; this is a blueprint for a home amenable to mass production.”

Rauch points out that many of the homes entered in the competition may be larger and fancier (with solar/electric system costs as high as $200,000 versus a little over $33,000 for Natural Fusion), but the Penn State team wanted to build a home that could change public perception. Natural Fusion utilizes modular construction and a roof-top PV system called Green Roof Integrated Photovoltaics (GRIPVs; pronounced “grip-vees”) where the properties of the green roof beneath the panels create greater efficiency in powering the house. “By using a green roof under our panels, the cooling effect the plants have being underneath actually makes the electrical system run more efficiently,” says Rauch. He points out that Penn State has the #1 Green Roof research program in the U.S., where trays of desert-hardy plants like sedum, through their transpiration effect, actually cool the air underneath the roof-top PV system.

Cylindrical PV

Unlike traditional flat-panel PV solutions in the Solar Decathlon (from BP Solar, Sunpower, SANYO Energy, General Electric, and Siliken), Solyndra cylindrical PV panels capture more sunlight throughout the entire day and perform optimally when mounted horizontally (flat), compared to traditional PV panels that are typically tilted or track the sun for maximum solar-energy production.

The secret to the improved solar-gathering power of Solyndra cylindrical PV is the unique architecture of the panels. Solyndra begins with a glass tube and uses thin-film deposition techniques to deposit the required copper indium gallium diselenide (CIGS) materials on the exterior of the tube. In a unique laser-scribing process (shown in videos on the Solyndra website at, the tube is spun about its longitudinal axis and the required regions are selectively ablated by the laser to pattern the thin films into cylindrical cells. A second glass tube is placed over the PV tube and a material with an optimized refractive index is added within the gap to direct solar energy from the exterior tube to the interior PV tube surface. Metal caps are fused onto the tube ends for electrical contacts, creating a hermetic glass-to-metal seal. The tubes are then connected in parallel, with approximately 40 tubes comprising a 1.0 m x 1.9 m panel.

“Our production panels have an average rated power close to 200 W. The cylindrical cells improve energy collection because the sun sees the same shape throughout the day,” says Kelly Truman, VP marketing and business development for Solyndra. “The air gaps between the glass tubes enable improved light collection, lower operating temperatures, and less impact of soiling. Due to the high energy yield per panel and the high area coverage from horizontal mounting, Solyndra panels are able to produce more solar electricity from low-slope rooftops than conventional flat-panel solutions.” Because mounting hardware can be half the cost of a PV system, Kelly adds that the open tube structure reduces wind loading on the Solyndra panels for lower-cost mounting.

On September 22, U.S. Treasury Secretary Tim Geithner and Energy Secretary Steven Chu hosted a group of clean energy developers and manufacturers at the White House to discuss how the American Recovery and Reinvestment Act is creating jobs and helping expand the development of clean, renewable domestic energy. At the meeting, Geithner and Chu announced $550 million in new awards through the Recovery Act’s 1603 program, bringing the total to more than $1 billion awarded to date to companies committed to investing in domestic renewable energy production. Among the meeting participants was Solyndra CEO Chris Gronet. Solyndra is helping to provide energy to a building in downtown Denver, CO through solar panels on the roof--a project that would not have been possible without Recovery Act payments.

--Gail Overton

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