In a collaboration between Dutch research institute TNO and the province of Limburg, researchers developed a smart, transparent thermochromic coating for windows, which when it reaches a certain temperature, switches from the transmission of solar heat to blocking it.

The built environment in the Netherlands is responsible for 40 per cent of energy use, and almost a third of CO2 emissions. The energy demand for a building is strongly influenced by the windows, which is where the invention can play a role.

The smart windows feature a temperature-sensitive glass coating of vanadium dioxide mixed with other ingredients. The new coating is thermochromic, which means that when it reaches a certain temperature, the optical properties change. The material has a good transparency around 20 degrees Celsius (room temperature). Only the transparency for infrared changes, but this does not affect the colour. When it is colder outside than 20 degrees, infrared light can pass through. When it is warmer than that, the infrared light is blocked. This ensures the window to save as much energy as possible, while remaining optically transparent.

Since the coating is thermochromic, there is no electricity or other special requirements necessary. The windows can be placed in normal window frames.

The researchers expect that a house with smart windows can save up to 400 kilograms of CO2 emissions, and up to 500 euros in energy costs in a house with airconditioning.

Currently, TNO is looking for partners to produce the so-called SunSmart windows and bring them to the market.

Image: TNO