The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) and Alta Devices have jointly demonstrated that Alta's solar material retains its high efficiency in real-world conditions, particularly on hot days. The primary reason is that Alta's modules stay cooler and lose very little efficiency as the temperature rises.

Combined with Alta Devices' energy density advantage, this has the potential for significant benefits, specifically in roof-integrated applications such as automobiles and buildings.

According to Sarah Kurtz, PhD, Principal Scientist, Reliability Group Manager of NREL, "To truly understand how much energy a particular solar technology will generate, it's critical to know how it performs in real-world conditions.

Alta's ability to retain its efficiency advantage at high temperature is an important benefit. 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. Alta's technology provides a fresh approach to these attractive applications by naturally rejecting heat and being less sensitive to high temperatures."

In a paper presented at the IEEE PVSC (Photovoltaic Specialists Conference) this week, the NREL-supervised tests and results were described. 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 Devices module operated cooler than conventional modules (up to 10 Celsius cooler when the sun was brightest) and the Alta module was about five times less sensitive to increased temperature. In fact, because of changes in the sun's spectrum associated with hot days, the Alta 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 the Automotive Industry
According to Alta Devices president and CEO, Chris Norris, "We are always excited about these kinds of results because of what they mean to customers and users benefiting from our products. This advantage is key for any roof-integrated application of Alta Devices products. 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. Our technology addresses both of these problems."

For example, the roof of a hybrid electric vehicle outfitted with an Alta Devices based solar array to generate electricity from the sun will run cooler, and continue to perform well in higher temperatures versus a silicon-based roof.

This provides more overall energy and allows the interior of the car to stay cooler, further reducing the power demand for air conditioning. Norris explained, "Our technology delivers tangible economic benefits to automobile manufacturers by helping them meet the latest CAFE standards while providing real-world benefits to the end users."