Researchers at the Royal Melbourne Institute of Technology (RMIT) have devised a method for applying vanadium dioxide (VO2) directly to glass to create smart windows.
(Credit: RMIT)
The VO2 coating, which is just 50-150 nanometres thick, allows glass to regulate the amount of heat that passes through depending on the temperature. Below 67°C, VO2 acts as an insulator. Above that temperature, the substance turns opaque to infra-red solar radiation while remaining transparent to the human eye. Thus, the sun’s heat is prevented from passing through the clear glass. The research is published in Scientific Reports.
According to Associate Professor Madhu Bhaskaran, lead investigator on the project, the breakthrough could help meet future energy needs and create temperature-responsive buildings.
“We are making it possible to manufacture smart windows that block heat during summer and retain heat inside when the weather cools,” she said. “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.
“Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital.”
While the tuneable nature of vanadium oxide has long been known, it had previously not been possible to use it in smart windows without specialised substrates that retained the material’s functionality. According to the RMIT team, its approach enables crystalline, switchable VO2 on any substrate, including glass, silicon and quartz. Furthermore, the coating’s reaction to temperature can be overridden with a simple switch.
“This switch is similar to a dimmer and can be used to control the level of transparency on the window and therefore the intensity of lighting in a room,” said co-researcher and PhD student Mohammad Taha. “This means users have total freedom to operate the smart windows on-demand.”
The technology, which has been filed for patent in Australia and the US, is said to be readily scaleable for large surfaces such as the facades of skyscrapers.
Whatever happened to Pilkington’s Smart glass: The concept of a material which altered its parameters depending on the input! I do recall an interview with this firm in 1963/3. They were enhancing so-called ‘float glass’ at that time: floated on a moulton bed of mercury? I recall being particularly impressed by the fact that the Pilkington family member who had the original idea had got this from watching the bubbles of washing-up liquid re-acting with the surface of the water as he assisted his wife one evening with clearing and cleaning the dishes after supper.
This made me remember a commercial product that was presented to me as a “panacea”: an automotive window film that used Fabry-Perot interference phenomena to filter IR… The local representative from Singapur made a bet: that their film was going to lower the internal temps of a car parked under the tropical sun. I carefully rigged a test to measure actual temperatures inside the parked car, only to discover that the entire concept was flawed: the INITIAL temperatures, from the sunrise and up to one or one-and-a-half hours later, was indeed SLIGHTLY lower than without the film… BUT, after that time, the windshield (and every window on the car) started to heat up because the film is adhered on the interior surface of them, and as the glass is heated by the sunrays IR wavelenghts, it becomes so hot that it starts to re-radiate the heat to the car interiors, which become practically as hot as if there was not any film! The flawed demonstration at the Expo where I first saw that film, was in a different environment: a 150 watt incendescent spotlight was placed on the right side of a film covered glass, which was held upright in the free air, thus the heat was dissipated and the difference among a bare glass and a film covered was impressive. But in a parked under the sun, closed windows car, the film made a too little difference to pay the film’s very high price only to have a very slightly cooler car for the first hour of the day or so.