Smart Window Blocks Heat, Generates Electricity

Buildings are going green and so it’s no surprise that researchers are working to develop smarter windows.
Among the smartest is a window designed by researchers at Shanghai University, led by Yanfeng Gao, which does triple duty: It’s transparent, regulates temperature fluctuations and doesn’t require external power to work.

The team’s goal was to find a way to merge a window with the power-generating capabilities of a solar panel, which typically isn’t transparent. Ideally, the researchers wanted to develop a window that would change its optical properties in response to temperature and do it without requiring power.
The answer was vanadium oxide. Gao’s team sandwiched a thin film of vanadium oxide between two layers of polycarbonate, the same material used in strong eyeglasses.
At room temperature, the polycarbonate panels appeared transparent. In fact, up to temperatures of 154 degrees Fahrenheit (68 C), the panels allowed heat — infrared light — to pass through. But once the temperature rose above that, the VO2 turned metallic and started reflecting the infrared wavelength, even though the panels appeared transparent to the eye.
In addition to regulating the wavelength of light, the vanadium also scattered some of the light to the sides of the panel. That’s where Gao’s group put a simple photovoltaic cell, which faced into the glass from the edge. In their experiment, sections of smart glass only a few inches on a side powered a 1.5-volt lamp.
Such a window would likely be more expensive than simple glass panes. But Gao and his co-authors noted in their study that buildings eat up 30 to 40 percent of the energy humans produce, and it all goes to heating, cooling and lighting. So a smart window like this could make a dent in that percentage.
The research is described in the current issue of the journal Scientific Reports.