The US Department of Energy's National Renewable Energy Laboratory (NREL) and Alta Devices of Sunnyvale, CA, USA have jointly demonstrated that Alta's solar material retains its high efficiency in real-world conditions, particularly on hot days. Alta says that the primary reason is that its modules stay cooler and lose very little efficiency as the temperature rises. Combined with its energy density advantage, this has the potential for significant benefits, specifically in roof-integrated applications such as automobiles and buildings, the firm claims.
"To truly understand how much energy a particular solar technology will generate, it's critical to know how it performs in real-world conditions," notes Sarah Kurtz PhD, principal scientist, Reliability Group Manager, at NREL. "For years, the industry has desired a very efficient solar cell that could be built into the roof of a car or building without paying the performance penalty associated with a hot roof," she adds. "Alta's technology provides a fresh approach to these attractive applications by naturally rejecting heat and being less sensitive to high temperatures."
The NREL-supervised tests and results were described in a paper presented at the 39th IEEE Photovoltaic Specialists Conference (PVSC 39) in Tampa, FL (16-21 June). The tests were conducted at NREL's outdoor testing facility in Golden, Colorado, measuring energy and operating temperatures over a nine-week period.
The result was that the Alta module operated cooler than conventional modules (up to 10°C cooler when the sun was brightest) and was about five times less sensitive to increased temperature. In fact, because of changes in the sun's spectrum associated with hot days, the module showed higher efficiencies on hot days than on cold days. In a simulation model using measured temperature coefficients (neglecting spectral effects), compared to a silicon module with the same power rating, the Alta module was predicted to generate 8% ± 2% more energy per year in Phoenix, Arizona. To the extent that these simulations were performed based on a rack-mounted configuration, it is expected that roof-integrated installations will show even greater benefit.
Benefits for automotive industry
"Up until now, integrating PV material directly into a roof of any kind resulted in additional heat needing to be dissipated, and a reduction in power output in the hottest part of each day, usually when you need it most," says Alta's president & CEO Chris Norris. "Our technology addresses both of these problems."
For example, the roof of a hybrid electric vehicle outfitted with an Alta-based solar array will run cooler and continue to perform well in higher temperatures versus a silicon-based roof, he adds. This provides more overall energy and allows the interior of the car to stay cooler, further reducing the power demand for air conditioning. "Our technology delivers tangible economic benefits to automobile manufacturers by helping them meet the latest CAFE (Corporate Average Fuel Economy) standards while providing real-world benefits to the end-users," concludes Norris.
