Perovskite-based Thermochromic Solar Windows Reduce Carbon Emissions in High-Rise Buildings

Scientists recently tested out a new solar panel product that adheres to the surface of the windows in high-rise buildings. It is a perovskite based clear material coating that windows, which absorbs energy from the sun and creates energy for the building while at the same time absorbing sunlight coming into the building's windows, thereby reducing the heating load in the summer. Lance Wheeler, the principal investigator on the project, stated in a recent interview that switching to thermochromic windows saves a significant amount of energy annually, with the main savings coming from the reduce need for heat energy for highly glazed office buildings in cold or seasonal cold climates. One interesting fact about this proposed energy savings is that if all the workers in the simulated office building drove an electric vehicle the distance of an average American commute, then the savings in annual energy from the thermochromic windows could be used to fully charge every worker’s car every day throughout the year.

These findings are detailed in the paper “Thermochromic Halide Perovskite Windows with Ideal Transition Temperatures,” which appears in the journal Advanced Energy Materials. The research, which relied on modeling software Wheeler helped develop called PVwindow, suggests adding a thermochromic laminate onto a single-pane or even double-pane window will yield significant savings. This is important information because high-rise buildings like those in Denver, Colorado account for about 40% of all primary energy consumption in the United States, with heating making up the largest contributor! This coating technology can be a revolutionary advance in both window energy efficiency that has been growing since the 1980s by selectively absorbing or reflecting infrared light but allowing light in the visible portion of the solar spectrum to pass through the glass. However, slightly more than half of the sun’s energy occurs in the visible wavelengths, so this technology could be the quantum leap required to significantly reduce the current 40% energy consumption of high-rise buildings with significant glass facades.

The researchers ]model building was a 12-story structure with a window-to-wall ratio of 95%. They simulated energy use in the building in 15-minute intervals for a year in eight climate zones across the country, covering Hawaii, Arizona, California, Colorado, New York, Wisconsin, Minnesota, and Alaska. The scientists concluded the following to be true:

1. Thermochromic double-pane windows improved building energy efficiency over double-pane windows in each zone.

2. Energy savings were greater in the colder regions of Colorado, New York, Wisconsin, Minnesota, and Alaska.

3. Thermochromic double-pane windows outperformed even triple-pane windows in the hottest climate zones of Hawaii, Arizona, and California.

The researchers noted that in colder climates triple-pane windows did provide more energy savings than the thermochromic double-pane windows, but when they added a thermochromic laminate to the triple-pane window, that provided the most annual energy savings compared to the highest efficiency triple pane windows. Scientists in the area of renewable energy research from NCEL will continue to test and adjust the placement and efficiency of the perovskite solar laminate, and they anticipate this being a bright future for the construction of new buildings and the renovation of current ones