Green Cities

The Future of Green: Smart Windows

**This is the third installment of our new blog series: The Future of Green. Every other Friday we will post a blog about a cutting-edge and futuristic innovation in the world of green technology. Technology is one of several barriers that stand between today’s society and a sustainable future. The innovators we highlight through The Future of Green are shattering those barriers. Make sure to tune in every other Friday for a glimpse into the future of energy and sustainability. Imagine smart windows that could control the amount of light and heat that get through. Such an invention would revolutionize energy efficiency in homes and buildings. Researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory are turning that vision into a reality. They have designed a material that is “a thin coating of nanocrystals embedded in glass that can dynamically modify sunlight as it passes through a window. Unlike existing technologies, the coating provides selective control over visible light and heat-producing near-infrared (NIR) light, so windows can maximize both energy savings and occupant comfort in a wide range of climates.” The ability to regulate visible light and NIR light—both together and separately—means that people can customize window settings based on their climate, the season, or the time of day. The potential energy savings from this technology are extraordinary. “In the US, we spend about a quarter of our total energy on lighting, heating and cooling our buildings,” said Delia Milliron, the study’s lead researcher. “When used as window coating, our new material can have a major impact on building energy efficiency.” Milliron’s research group had previously developed a smart-window technology that regulates NIR by sending a small jolt of electricity through the material to switch back and forth between NIR-transmitting and NIR-blocking states. This technology only allowed the glass to control NIR, whereas their newest material can regulate NIR and visible light. On a summer evening, for example, people could choose to allow more visible light in, while blocking NIR light to maintain a comfortable temperature. This would reduce the need for air conditioning and artificial lighting, thereby saving energy. On a winter day, users may choose to let NIR light and visible light in, allowing them to save on heat and lighting. The material’s two functionalities—control over visible light and control of NIR light—result from “nanocrystals of indium tin oxide embedded in a glassy matrix of niobium oxide.” The nanocrystals and the matrix actually have a synergistic relationship, “which means that they can use thinner coatings without compromising performance. The key is that the way atoms connect across the nanocrystal-glass interface causes a structural rearrangement in the glass matrix. The interaction opens up space inside the glass, allowing charge to move in and out more readily. Beyond electrochromic windows, this discovery suggests new opportunities for battery materials where transport of ions through electrodes can be a challenge.”

The technology is clearly in its beginning stages, and it will be likely be a long time before it’s commercially available and affordable; nonetheless, it has the potential to revolutionize the built environment and minimize the amount of energy consumed in homes and buildings. Check back in two weeks to learn about another innovation in the world of green technology! And be sure to revisit the first two installments in The Future of Green: floating offshore wind turbines and The Hyperloop.