The New Smart Windows

An example of the self-darkening glass next to a normal pane of glass in sunlight.

New 'Smart Windows' Let In Light But Keep Out The Heat For Energy Savings: A new nanocrystal glass has the ability to control the light and heat that gets through it, which means it could be used to make "smart windows" that could drastically reduce electricity bills. The new nanotechnology-based smart windows, the details of which are published in the journal Nature on August 15, could drastically lower energy bills by decreasing the electricity used to light a house while also lowering air conditioning bills on hot days.

Windows coated with this material could be integrated with a climate control system that a user could program to change with the time of day, or respond to fluctuations in sunlight or outside heat. "You would probably hook this up to some sort of control system that monitors light and heat and adjusts the window as needed," study researcher Delia Milliron, of Lawerence Berkeley National Laboratories, told Business Insider. "But you would always have an override switch if that was your preference, if it was too bright or if you wanted to darken it."

Nanocrystals of indium tin oxide (shown here in blue) embedded in a glassy matrix of niobium oxide (green) form a composite material that can switch between NIR-transmitting and NIR-blocking states with a small jolt of electricity. A synergistic interaction in the region where glassy matrix meets nanocrystal increases the potency of the electrochromic effect.

Nanotech to the rescue - Smart windows made from electrochromic glass work by darkening when a low voltage current is sent through them. A coating on the glass reacts to current and changes color, blocking the light. This idea isn't new — electrochromic windows exist in buildings and homes, and even Boeing's Dreamliner's First Class cabin windows.

One drawback of currently available self-darkening windows is that they can't let in a lot of sunlight without also letting in the sun's heat. "That was sort of an outstanding challenge that had been sitting in the background of the smart windows or high-performance windows field for a long time," Milliron said. The researchers solved this problem by mixing the Niobium oxide with special nanocrystals that can block the near-infrared rays that carry heat from the sun.

The inset represents the small nanocrystals suspended in the Niobium oxide. The window to the left shows the three possible settings of which the material is capable. The top shows the window without any charge: allowing both light and heat through. The middle setting blocks most of the near-infrared (heat) rays, while still allowing light waves through. In the bottom, the window is blocking both heat and light.

A new dawn - To make the revolutionary new windows, heat-absorbing nanocrystals are "grown" in a flask, and then mixed with a light-absorbing compound called Niobium oxide that, when heated, will encase them in a glass-like structure. They coat a standard piece of window glass with the solution, and heat the whole thing to bond the film to the glass. What comes out on the other side is a sheet of glass layered with a thin film of nanocrystals that can be programmed with electrical charges. This makes manufacturing the new smart windows much cheaper and quicker than before, opening up a much larger market for the technology.

It could be included in homes, large buildings and in cars, and could have a huge impact on energy costs, especially in hotter climates. "In the US, we spend about a quarter of our total energy on lighting, heating and cooling our buildings," Milliron said in a press release. "When used as a window coating, our new material can have a major impact on building energy efficiency." But, there still is more work to do. First, the team needs to integrate this new material with preexisting smart window components that regulate the voltage to activate the color and heat blocking features before they can have a full prototype.