NREL develops window that reduces cooling load and generates electricity

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) report a breakthrough in developing a next-generation thermochromic window that not only reduces the need for air conditioning but simultaneously generates electricity.

Heat generated by sunlight shining through windows is the single largest contributor to the need for air conditioning and cooling in buildings. Because residential and commercial buildings use 74% of all electricity and 39% of all energy in the United States, the shading effect from tinting windows helps buildings use less energy.

The technology, termed “thermochromic photovoltaic,” allows the window to change color to block glare and reduce unwanted solar heating when the glass gets warm on a hot, sunny day. This colour change also leads to the formation of a functioning solar cell that generates on-board power. Thermochromic photovoltaic windows can help buildings turn into energy generators, increasing their contribution to the broader energy grid’s needs. The newest breakthrough now enables myriad colors and a broader range of temperatures that drive the color switch. This increases design flexibility for improving energy efficiency as well as control over building aesthetics that is highly desirable for both architects and end users.

The research builds upon earlier work at NREL into a thermochromic window that darkened as the sun heated its surface. As the window shifted from transparent to tinted, perovskites embedded within the material generated electricity. Perovskites are a crystalline structure shown to have remarkable efficiency at harnessing sunlight.

“A prototype window using the technology could be developed within a year,” said Bryan Rosales, a postdoctoral researcher at NREL and lead author of the paper, “Reversible Multicolor Chromism in Layered Formamidinium Metal Halide Perovskites,” which appears in the journal Nature Communications.