NASA Touts New Hybridized Solar Cell

In their pursuit of more efficient and more durable solar cells that can better resist the harsh space environment, NASA researchers have announced success in blending typical silicon-based solar cells with gallium arsenide cells.

Researchers from the NASA Glenn Research Center, the Massachusetts Institute of Technology and Ohio State University say the new hybrid cell is more efficient, durable and lightweight than their standard fare. The new technology may never reach an acceptable cost-per-watt to be useful for commercial solar applications, but it could improve the way solar is used to power space-based applications. Most solar cells are made from silicon, an element used in computers. For space-based applications, some cells are made of gallium arsenide, a chemical compound often found in mobile phones. Both materials have worked for years in space, but each has its own strengths and weaknesses. For instance, gallium arsenide solar cells produce twice as much power as silicon and are more durable, while silicon solar cells weigh less and conduct heat better. “Engineers have been trying to merge gallium arsenide solar cells with silicon for about 20 years,” said Glenn Electrical Engineer David Wilt. “We believe we’ve overcome the problems they’ve had in the past.” The Glenn team combined the best properties of each type of cell by depositing gallium arsenide layers on a silicon base. According to Wilt, the resulting hybrid cells can be manufactured to cover a much larger area than existing ones. That means solar arrays could be “highly efficient, about twice as light and much cheaper,” Wilt said. The hybrid cells are part of the Forward Technology Solar Cell Experiment (FTSCE), which Astronaut Soichi Noguchi installed outside the international space station during STS-114. FTSCE is a part of the Materials International Space Station Experiment (MISSE), a collection of hundreds of material samples mounted on the outside of the space station. A collaborative effort between Glenn and the Naval Research Laboratory, FTSCE also contains advanced solar cells produced by the private industry. Researchers are studying how these new solar cells perform and endure in space. “Even though we have sunshine, rain and wind on Earth, space is a much more brutal environment,” said FTSCE Systems Engineer Phillip Jenkins. “Among other things, materials in space have to withstand radiation and extreme temperatures.” To monitor the experiment, Glenn engineers designed, built and programmed a data-acquisition system that takes measurements on command or automatically based on temperature, time and the position of the sun. A transmitter built by the U.S. Naval Academy then relays that data to researchers on Earth. “The experiment is facing the sun, so it’s vulnerable to a lot of solar flares and radiation,” said Electronics Engineer Michael Krasowski. “So far, we haven’t seen a single hiccup in the data acquisition system.” The 10-circuit-board data-acquisition system is much smaller and lighter than most electronics built to withstand space. The entire experiment, including the test cells and electronics, fits into a 2-foot by 2-foot by 4-inch container. FTSCE is scheduled to remain on the space station for one year. Just in case the test period is extended or the transmitter fails, Krasowski and the electronics team equipped the experiment with enough memory to collect data for more than two years. This isn’t the first time FTSCE’s electronics and photovoltaics teams have collaborated on groundbreaking experiments. The teams also built the Wheel Abrasion Experiment and the Materials Adherence Experiment, components of the 1996 Mars Pathfinder mission. Those experiments measured the effects of dust on the Rover Sojourner’s wheels and solar panel. When FTSCE returns, researchers will compare the data stored in its memory with the data transmitted from space. The new solar cells eventually could be used to power space systems traveling to Jupiter.
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