'Smart Windows' Darken to Cool, Become Solar Panels When Hot

The smart windows, developed at NREL, provide a cleaner cooling solution than AC.
Chris Young
NREL researcher Lance Wheeler holds samples of perovskite window techDennis Schroeder/NREL

Anyone who lives in a hot country knows that blackout blinds don't only keep the light out, they also keep the heat out. But what if, instead of simply blocking that light, we could harvest it for energy?

Scientists have recently unveiled new research into "smart windows" that not only change color automatically when heated by sunlight to keep buildings cool, they also double up as solar panels.

The research poses a double whammy of clean energy benefits as it provides solar energy at the same time as reducing a building's reliance on air conditioning.


Smart windows that double up as solar panels

In a new paper titled "Reversible Multicolor Chromism in Layered Formamidinium Metal Halide Perovskites," researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) detail a "thermochromic photovoltaic" tech that switches colors when heated by sunlight to reduce the need for cooling.

Not only that, when the smart windows get darker, they also start collecting energy from the same sunlight that gives them their darker hue.

The windows are made from a thin sheet of the increasingly adopted solar cell material perovskite, which is placed in between two panes of glass, with a solvent vapor injected in between the two.

The vapor causes the perovskite crystals to rearrange themselves at higher temperatures, first into a chain, then a sheet, and then a cube. Each shape changes the window's color, blocking sunlight to different degrees.

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Cleaner cooling

The shifts in color occur between 95 and 115 °F (35 and 46 °C), a higher range than previous prototypes made by the same team. The new windows can shift from transparent to yellow, orange, red, and brown, in approximately seven seconds.

"A prototype window using the technology could be developed within a year," Bryan Rosales, a postdoctoral researcher at NREL and lead author of the paper, explained in a press release.

With several new technologies pointing the way to cleaner cooling, such as these 'cold tube' panels that allow users to keep their windows open without losing energy, here's hoping that the air conditioning of the future isn't a strain on our environment.

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