Smart windows make climate-neutral living more attainable

There are more than 7 million buildings in the Netherlands, which together currently account for 40% of our energy consumption. The built environment also accounts for almost a third of carbon emissions. To meet the requirements of the Paris Climate Agreement, all homes and offices need to become substantially more sustainable.

The intended end result is an energy- and climate-neutral built environment by 2050, which will require innovations to help reduce energy consumption. In addition to solar panels and heat pumps, smart windows could soon start making a significant contribution to energy and emissions reduction.

Air conditioning and heating can be turned off more often

TNO is currently working on the SunSmart smart window, which has a special coating. This thermochromic layer helps regulate indoor temperatures by blocking solar heat in summer and letting it through in winter. As a result, smart windows can reduce the use of air conditioning and heating, and thus cut energy consumption. With this innovation, an average household could save around 400 kg of CO2 on an annual basis, plus hundreds of euros on energy bills.

Making windows smart

The special feature of the SunSmart smart window developed by TNO is that the thermochromic coating itself switches between letting in and blocking solar heat at a fixed temperature. Current electrochromic solutions use a motor or electricity and are therefore more expensive and less sustainable.

The SunSmart smart window’s ability to switch is an intrinsic feature of the coating material, which has been optimised for use in this application after years of research.

Advantages over electrochromic glass coatings

Electrochromic glass coatings are costly because they use electronics to switch between letting in and blocking solar heat. In addition, they also cause the windows to change colour. The SunSmart smart windows TNO is working on are affordable and feature integrated temperature regulation. Moreover, the coating is transparent and the window does not change colour, increasing its applicability for architects.

This is how smart windows work

The smart windows feature a temperature-sensitive glass coating of vanadium dioxide mixed with other ingredients. Depending on the temperature, this layer either allows the sun’s infrared light to pass through or blocks it. TNO has managed to bring the switching temperature to exactly 20 degrees Celsius, or room temperature.

If it is colder outside, the smart window allows solar heat to pass through, so the heating system does not have to work as hard. If it is warmer than 20 degrees outside, the coating blocks thermal radiation. It then stays more comfortable inside and the air conditioning does not have to be turned on as often.

The smart window therefore offers benefits in all seasons. The thermochromic coating is primarily designed for temperate climates in large parts of Europe and the US, but the switching temperature can be relatively easily adapted to other climate zones.

Affordable innovation

While developing the smart windows, TNO explicitly considered the affordability of the raw materials as well as the production process. As a result, SunSmart thermochromic windows have a payback period of 5 to 7 years. This is roughly comparable to the investment in solar panels.

According to TNO, air-conditioned homes could save around 500 euros a year on their energy bills thanks to thermochromic windows. Another sustainable feature is that the windows are also durable, with a guaranteed service life of 20 years.

Other applications

An innovative collaboration between Yparex and Brightlands Materials Center (BMC) has led to the development of a revolutionary glass film that can be invisibly incorporated into window glass. This film has the same properties as smart windows. The crucial ingredient of this film is a special pigment developed by BMC. Yparex, which specialises in plastic films, mixed the pigment with a special plastic to produce a film (POE) that can be effortlessly added to laminated glass.

From pilot line to large-scale production

Now that TNO has shown that the SunSmart smart windows can effectively contribute to meeting the climate challenge, it is time to scale up the production process. In the pilot line at the TNO-Brightlands Materials Center in Geleen, a mini-test plant is now working overtime.

In a dust-free environment, TNO applies the thermochromic coating to the perfectly clean glass using the roller-coater technique. The coating then hardens in an oven. These thermochromic windows will be ready for large-scale production by 2025, which will also make the technology commercially interesting.