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Dynamic Solar Windows Do Double Duty

Feb. 5, 2018

A new discovery could increase the value of switchable thermochromic windows.

Smart windows that darken in response to too much sun are already gaining ground commercially, but a new discovery could add even more value.

Scientists at the DOE’s National Renewable Energy Laboratory (NREL) have developed a thermochromic window that not only darkens automatically in response to sun, but also generates electricity during the darkening process.

Methylamine molecules are driven out of the device in response to solar heat, which darkens the window. When the sun is no longer shining and the device cools back down, the molecules are reabsorbed and the window appears transparent.

The untinted window allows in an average of 68% of light in the visible portion of the solar spectrum, while the tinted version only allows about 3% through. The window changed color completely in around 3 minutes during testing.

“There is a fundamental tradeoff between a good window and a good solar cell,” explains Lance Wheeler, a scientist at NREL. “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.”

The window achieved a solar power conversion efficiency of 11.3%. Ongoing research will focus on improving performance stability with the aim of eventually integrating it into buildings, vehicles and electronics. 

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