Scientists at the National Renewable Energy Laboratory (NREL) of the US Department of Energy reported that a breakthrough has been made in the development of next-generation thermochromic windows that can not only reduce the need for air conditioning, but also generate electricity at the same time.
The heat generated by sunlight through windows is the largest contributor to air conditioning and cooling needs in buildings. Since residential and commercial buildings consume 74% of electricity and 39% of energy in the United States, the shading effect of tinted windows helps buildings use less energy.
This technology, called "thermochromic photovoltaics," allows windows to change their color to block glare and reduce unnecessary solar heating when they get warm on hot, sunny days.
This color change also leads to the formation of functional solar cells that can generate onboard power. Thermochromic photovoltaic windows can help buildings turn into energy generators, increasing their demand for a wider energy grid.
With the latest breakthrough, countless colors and a wider temperature range can now be achieved to drive color switches. This increases design flexibility to improve energy efficiency, as well as control over architectural aesthetics, which is very necessary for architects and end users.
This research builds on NREL`s early research on thermochromic windows, which darken as the sun heats its surface. As the windows change from transparent to colored, the perovskite embedded in the material generates electricity. Perovskite is a crystalline structure that has been proven to have significant efficiency in the use of sunlight.
NREL postdoctoral researcher Bryan Rosales (Bryan Rosales) said: "Prototype windows using this technology may be developed within a year." His thesis "Layered formimide metal halide perovskite "Reversible Multicolor Chromism In Layered Formaidium Metal Halide Perovskites" was published in "Nature Communications" magazine.
The first-generation solar windows were able to switch back and forth between transparent and reddish brown, requiring temperatures between 150 degrees Fahrenheit and 175 degrees Fahrenheit to trigger the conversion. The latest version allows a wide range of color choices, and the operating temperature is between 95 degrees Fahrenheit and 115 degrees Fahrenheit, which is a glass temperature that is easily reached on hot days.
By using different chemical compositions and materials, researchers can also quickly speed up color conversion. The time was shortened from 3 minutes required for the proof-of-concept thermochromic photovoltaic window shown in 2017 to about 7 seconds.
The scientists sandwiched a thin perovskite film between two layers of glass and injected steam. The water vapor initiates a reaction, causing the perovskite to arrange itself into different shapes, from chain to flake to cube. The color appears as the shape changes. Lowering the humidity will return the perovskite to its normal transparent state.
They will also plan to conduct more research. One area to explore is the number of times that thermochromic windows can cycle into the power generation operation mode and return to transparency. They will also explore the efficiency of converting sunlight into electricity.