There are already energy-saving "smart glass" windows that can be electronically tinted to block the sun's hot rays, thus reducing the need to run air-conditioning systems. Such systems still require electricity to operate, however. Now, scientists from Australia's RMIT University have developed a coating that allows existing glass to become smart … no power required.

Composed of relatively inexpensive vanadium dioxide, the self-regulating coating is just 50-150 nanometers thick. That's approximately 1,000 times thinner than a human hair.

At surface temperatures below 67 ºC (153 ºF), vanadium dioxide acts as an insulator, helping to keep indoor heat from escaping through the window glass – it also allows the full spectrum of sunlight to enter from the outside. At temperatures above 67, however, it transforms into a metal that blocks heat-causing infrared solar radiation from entering.

This means that rooms stay warmer when temperatures are lower and cooler when they're higher, allowing for less use of both heating and air-conditioning systems. Additionally, if users wish, they can override the coating's ray-blocking effect using a dimmer switch.

Previously, in order to apply vanadium dioxide coatings, specialized layers – or platforms – had to be created on the surface. The RMIT team, however, has developed a method of applying the coatings directly to surfaces such as window glass, without the need for platforms. It is now hoped that the system can be commercialized as soon as possible.

"Our technology will potentially cut the rising costs of air-conditioning and heating, as well as dramatically reduce the carbon footprint of buildings of all sizes," says lead scientist Prof. Madhu Bhaskaran. "Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital."

The research is described in a paper that was recently published in the journal Scientific Reports – Nature. Vanadium dioxide-coated smart windows are also being developed by scientists in the UK.

Source: RMIT