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US NREL develops thermochromic solar windows

Scientists from the US Department of Energy’s National Renewable Energy Laboratory (NREL) have developed thermochromic windows capable of efficiently converting sunlight into electricity.

The demonstration device is designed to dynamically respond to sunlight by transforming from transparent to tinted, while converting sunlight into electricity.

NREL said that the color change is caused by methylamine molecules that are reversibly absorbed into the window device.

When exposed to sunlight, the device is heated up and drives out the molecules, thus transforming from transparent to tinted to generate electricity.

During night or when the sun is not shining, the device is cooled back allowing the molecules to re-absorb into the window device, appearing transparent.

During testing, the 1cm² demonstration device allowed an average of 68% of light in the visible portion of the solar spectrum to pass through it when in transparent state.

However, once the window color changes, the device allowed only 3% of light.

NREL scientist Lance Wheeler said: “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.”

Wheeler said the technology has can be used on vehicles, buildings, among others while the produced electricity could be used to charge batteries to power smartphones or on-board electronics.

The NREL scientists are currently working to improve the cycle stability of the demonstration device, which showed declined performance over the course of 20 transparent-tinted cycles during the testing.


Image: The NREL’s new switchable windows can efficiently convert sunlight into electricity. Photo courtesy of Dennis Schroeder/NREL.