80 percent of the helicopter-mounted searchlights used by U.S. law enforcement, according to the company. A solar cell is a device used to convert sunlight into electricity. The cells are the building blocks that form photovoltaic modules, or solar panels. The International Space Station has 275,000 solar cells that generate up to 120 kilowatts, or about what it takes to power more than 100 households in the United States, the largest amount of power of any space vehicle in orbit. “There is the opportunity for evolution, and at the same time revolution, to change people’s lives for the better,” said Tony Mueller, Spectrolab president, of the solar cell. “You have to be on your ‘A game’ every single day because you know it has to work.” At Spectrolab, solar cells are created in a chemical reactor, which looks like a 3-foot-diameter (1-meter) stainless steel tank. The process takes 90 minutes. At high temperatures, gases, metals and other materials form crystal layers on germanium wafers. In a fabrication laboratory, solar cells are cut from the wafers, the layers forming triple-junction structures, with each layer capable of receiving a different color of light. “We grow different kinds of crystal to absorb different parts of the solar spectrum,” explained Jeff Krogen, senior director for photovoltaic metal organic vapor phase epitaxy, which describes the growth process. Solar panels are sized to fit the needs of the space vehicle, which mostly involve communications satellites. Spectrolab shipped out over 200 solar panels in 2015, many of them going to international customers. The panels come with a 25-year reliability life. Spectrolab’s most recent solar cell technology has a greater than 30 percent efficiency rate for turning each watt of sunlight into electricity—double what it was two decades earlier, according to the company. In the factory high bay area, technicians work on rectangular orange and black panels, soldering or snipping wires, applying liquid adhesive and tape, and cleaning debris particles off the surface. Panels are mounted on stands and are flipped over with the turn of a wheel. The work is so precise that Beth Chiodetti, a Spectrolab technician for 37 years, wears headgear replete with magnifying glasses and yet uses a separate hand-held magnifying glass, all to check solar panel connections. The goal for her and her colleagues is to build the solar panel right the first time in the factory, Chiodetti said. There is no room for error later on. “The mantra of launching something into space is this: Once it’s gone, you don’t get it back,” pointed out Chris Fetzer, chief engineer, epitaxy products. The cells must be perfectly mated on the panels to be properly exposed to the sun. The panels have robust glass covers and are tested for electrostatic discharge, one of the largest causes of failure during testing. Richard Smith, a 15-year Spectrolab technician, keeps track of everything he does on a color-coded paper taped to the panel. He makes sure all wires are soldered to tabs. He calls out a warning to others as he flips a panel over. “I’m very proud of the work that we do,” he said. “My name is on some of the stuff that’s on the Mars Orbiter and the Kepler satellite.” Depending on size, panels are completed in four and a half to six months. They need to be tested on- and off-site. They leave the factory packaged in a variety of containers, everything from metal crates to wooden boxes, wrapped in foam and shock mattresses. Spectrolab continues to look for ways to make panel production less time-consuming and more economical. That might involve finding new methods or applications to shave days or even weeks off the process. The 300-person Spectrolab team is highly skilled and experienced, said Jim Hanley, senior director, solar panel operations. “We’re around the periphery of space power,” Hanley said, standing in a room filled with 36 solar panels. “Nothing gets done here without it being done right.” Separate solar cells are either shipped directly to the customer after testing or assembled into CICs, which stands for Covered Interconnected Cells. Spectrolab uses a robot to MAY 2016 | 31
Frontiers May 2016 Issue
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