Greater PV Efficiency through Nano-Technology

a guest post by Ken Whiteside, Director of Business Development at ONTILITY, LLC.

Conventional photovoltaic solar cells are much more efficient than they were ten years ago. Cells are up from a conversion rate of less than 15 percent to more than 30 percent. They still miss a big chunk of the electromagnetic spectrum, though. The silicon semiconductors in a solar cell are geared toward converting visible and near infrared light directly to electricity. Even the most advanced broad spectrum cells let a lot of energy get away. That energy is lost to heat. Harvesting that heat and converting it to electricity is an area of significant research in the quest for more highly efficient PV cells. One of those efforts centers on a "thermal emitter."

What if we had a material that would absorb all that excess heat and turn it into visible and near infrared light that the PV cells could "see" and then convert to electricity? If we had such a material and redirected the heat that is now wasted, some researchers tell us, we could have solar cells with 80 percent conversion efficiencies.

Greater PV Efficiency through Nano Technology

Tungsten comes to mind. A hundred years of experience with light bulbs tells us two things about tungsten, it does indeed emit infrared and visible light when heated, and it isn’t terrifically durable. In fact, its ability to hold up in temperatures above 1800 degrees Fahrenheit (the kinds of temps seen in a thermal emitter application) led to such disappointing results that the whole idea was deemed not cost-effective.

Recently, however, researchers led by Stanford professor Shanhui Fan and Paul Braun at the University of Illinois have developed a way to use nano-technology to make tungsten more durable under intense heat. They are coating the tungsten structures with a nano-layer of hafnium dioxide, a ceramic. The early results are very promising. While the raw tungsten was breaking down at 1800 degrees Fahrenheit, the nano-coated surfaces operated without issue for 12 hours at that temperature, and at 2500 degrees Fahrenheit the material still lasted for an hour before breaking down.

This approach to improving solar cells is appealing for a variety of reasons. Both tungsten and hafnium dioxide are very plentiful and safe to work with. And thermal emitters work with existing solar cell technology, making it simple to add them to existing manufacturing processes.While this research doesn’t have an impact on our business today, it is refreshing to see that research and innovation continue. Technological innovation and improvement are the keys to a sustainable solar industry.

Ken Whiteside photo Ken Whiteside has been a fan of solar energy for decades. His first hands-on experience was installing solar on off-grid houses around Telluride, Colorado in the 1990’s (summer in the San Juan Mtns. - somebody had to do it). From his home in Austin, Ken writes and works for widespread adoption of solar electricity, smart energy production and use, and sustainability.

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