Solar Energy From These Color-Changing Windows Could Power Your Car or Home One Day

Employees row a boat as they check solar panels of a photovoltaic power generation project at a fishpond in Jingzhou, Hubei province, on August 23. Reuters

Updated | A new type of window developed by scientists works sort of like transitions lenses—the ones you can wear indoors or outdoors without scrambling between clear and tinted glasses in order to see—but the device generates electricity. And, it could help power your home, car, or entire office building one day.

These windows—dubbed "thermochromic" for their ability to change colors in response to heat—can convert sunlight into electricity using minerals called perovskites and single-walled carbon nanotubes. Perovskites have been used for solar energy research previously, but what is innovative about this device is how the window can transform from transparent to tinted in response to heat from sunlight.

"You can imagine that...any photovoltaic window technology has this sort of fundamental trade-off between a good window and a good solar cell because a good solar cell or solar panel is something that absorbs light very well," Lance M. Wheeler, lead author of the study published in Nature Communications last Thursday, told Newsweek. "If you absorb all the light, nothing comes through the window."

Considering how many square feet of windows there are—from people's homes to massive office buildings and skyscrapers and vehicles—solar technology fused with windows could increase renewable energy use.

"We're not trading off" the benefits, said Wheeler, a chemistry and nanoscience research scientist at the National Renewable Energy Laboratory. "That's really the revelation here."

NREL science in @NatureComms demonstrates proof-of-concept for a new switchable solar window that dynamically responds to sunlight by transforming from transparent to tinted while converting it into electricity -

— NREL (@NREL) November 27, 2017

The researchers were able to reach solar energy conversion efficiencies as high as 11.3 percent, and the switch between transparent and tinted appearance happens in under three minutes.

"It really does enable getting higher efficiencies because you can absorb a lot more of that light and convert a lot more of that light into electricity because you're able to tint it and dynamically respond to the sun," he said.

In between the layers of the solar cell, a gas called methylamine causes the color change by flowing in and out of the panel, depending on the temperature. As the temperature rises to at least 95 degrees Fahrenheit and the sun shines, the window darkens and the gas ejects out. When the sun recedes and it cools back down, the methylamine molecules are reabsorbed back into the window, appearing like a normal window.

Solar panels of local mining company CAP, which were installed by SunEdison, are seen in the Atacama Desert in this June 5, 2014, file photo. Reuters

Wheeler described potential uses for the windows, including: sides of buildings, cars with a panoramic sunroof, smartphone batteries, or electronics including fans, rain sensors and motors that would power on and off as programmed. Skylights and LED lighting at night could also benefit from the technology, he added.

How to stabilize the performance levels of the window is still unclear. Each cycle of heating and cooling restructures the color-changing cell. Over time, the frequent restructuring eventually diminishes the performance of the device.

"To improve, we have new device designs that will control how the film restructures after each cycle," said Wheeler. "We are validating new mechanisms to achieve a similar color-changing effect."

The product began its path to commercialization last year during a two-month program to develop a market strategy for the dynamic photovoltaic glass, called SwitchGlaze. The windows, once fully adapted for commercial use, could have the benefit of saving consumers money on their air conditioning bills—when temperatures are higher, the windows automatically become tinted.

"It certainly has this double benefit: One, of converting energy, and two, of sort of mitigating solar heat gain," Wheeler said. "It's a one-two punch."

This story has been updated with additional information about the performance of the device over time.