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NREL’s solar window creates brighter future for green building industry

Lance Wheeler (front) holding NREL’s thermochronic, solar window with (from left) Nathan Neale, Robert Tenent, Jeffrey Blackburn, Elisa Miller, and David Moore. (Photo by Dennis Schroeder/NREL)

Just last week, researchers from the U.S. Department of Energy’s National Renewable Energy Lab (NREL), published findings from one of their latest research projects- a window prototype capable of generating electricity from sunlight.

The solar window, known formally as a “Switchable Photovoltaic Window”, is thermochromic, meaning it changes color when exposed to heat. When NREL’s solar window prototype is exposed to heat from direct sunlight, methylamine molecules are driven out and the window tints automatically. Meanwhile, a photovoltaic inlay converts the sunlight into electricity. Once the window is no longer exposed to direct sunlight and begins to cool, it becomes transparent again.

Unlike traditional smart windows, that self-tint to reduce absorption of ultra-violet and infrared sunlight in buildings, NREL’s prototype would be the first and only window that combines self-tint smart windows, with photovoltaic technology. So these high-tech windows won’t just save building owners money by reducing building temperatures associated with afternoon sunlight exposure, they would also be capable of generating renewable energy onsite.

And perhaps most importantly, the prototype is switchable, meaning it will allow visible light to penetrate the windows when they aren’t generating energy- something researchers struggled with when developing solar window prototypes in the past. Given recent studies that prove how critical sightlines to nature and natural light are to the comfort and wellbeing of building occupants, their prototype offers the perfect solution for developers looking to maximize energy efficiency without sacrificing building comfort or design.

Lance Wheeler, an NREL scientist, explains. “There is a fundamental tradeoff between a good window and a good solar cell. This technology bypasses that. We have a good solar cell when there’s lots of sunshine and we have a good window when there’s not.”

In a recent press release, NREL reported that the prototype allows 68% of visible light to penetrate the pane when the window is in its transparent state. After approximately 3 minutes of direct sunlight exposure, the window is able to convert a little over 11% of the solar heat into useable energy.

Despite widespread excitement from researches and green building professionals, the prototype will need additional testing before it can be commercially produced. Currently, the window begins to lose its efficiency after just 20 cycles- not nearly enough to keep pace with the life of traditional smart windows, which can last for 50 years.

Once the switchable photovoltaic window is perfected, the applications are endless. NREL researchers hope that in addition to re-thinking traditional commercial building design, the same technology could one day be used in vehicles, smartphones and small electronic items. Perhaps someday, a switchable photovoltaic window could power your cell phone and an office fan, just as the afternoon sun is peaking and you’re badly in need of a re-charge.


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