Smart windows could spark energy efficiency revolution

Window coating can stop around 50% of heat and 70% of visible light, generating huge energy savings

Nanocrystals of indium tin oxide (shown here in blue) embedded in a green glassy matrix of niobium oxide (Pic: Berkeley Lab)

A window spray has been developed in the USA to respond to changing weather conditions, reducing the need for heating and air conditioning.

Scientists say tiny crystals applied to windows and activated by a small electric charge can either block radiation from outside or inside.

They report in the journal Nature that when ‘jolted’ with a charge, nanoscale molecules of indium tin oxide can absorb as much as 35% of heat.

When embedded in a glassy substance the composite material can stop around 50% of heat and 70% of visible light, and remains stable after being switched on and off 2,000 times.

The coating can be sprayed onto the inside of a glass pane. But turning the coating off and on requires applying a voltage directly to its surface.

In the lab scientists generated the voltage by incorporating the material into a battery. Out in the real world, thin, transparent films layered on top of the coating will be needed to supply that voltage.

Such modifications will make smart windows expensive, says Brian Korgel, a materials chemist at the University of Texas at Austin and the author of a News & Views article on the research.

If the technology is to be adopted, “the overall cost of the system cannot be prohibitively high”, he warns.

Energy savings could help to offset the large price tag, but developers are looking for ways to cut costs. One option may be to replace the expensive indium tin oxide with cheaper zinc-based crystals, which have already shown promise in the lab.

Around 4% of all energy consumed in the United States is used to cool or warm buildings to compensate for heat transfer through windows, according to the US Department of Energy.

In some cases the use of air conditioning can increase a building’s energy consumption and carbon emissions by up to 100%, while heating can account for 60% of your total energy use.

“The ability to perform well in hot and cold climates could mean big energy savings,” says Delia Milliron, a materials chemist at Lawrence Berkeley National Laboratory in Berkeley, California, who led the team that developed the material.

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