Color-changing window: lithium-filled glass (left) and clear glass (right). Photo by NREL.
Architects are well aware of the age-old energy conundrum presented by windows. Despite the fact that building occupants benefit from the daylight and views provided by windows, these glassy apertures cannot compete with the thermal performance of most building envelope materials—at least not on a budget. Electrochromic glass has garnered attention for its ability to absorb heat from the sun during the winter and reflect it in the summer, but at significant cost. Recently, however, scientists at the National Renewable Energy Laboratory (NREL) unveiled a new, cost-effective version of electrochromic windows that employ spray-on films. These films not only make the windows cheaper, but also perform better. Now, the goal to make windows capable of changing with the weather may arrive sooner than we expected.