A two-layered paint that reflects infrared light while maintaining its colour could help keep buildings and vehicles cool under hot sun. This could help reduce energy used in cooling, such as by air conditioners.
This coating was developed by Yuan Yang at Columbia University in New York and his colleagues. It consists of a top layer of commercial paint, which provides the colour, and a bottom layer made of a polymer similar to Teflon, which reflects infrared light.
Sunlight contains both visible and infrared light but the infrared accounts for the majority of the solar energy, says Yang.
When the sun shines on an object coated with this paint, the top layer absorbs certain wavelengths of light, depending on the paint’s colour, while the bottom layer reflects infrared light, preventing the object from heating up.
A similar cooling effect can be achieved using white paint or metal mirrors, but Yang says the advantage of this new paint is that it can be any colour desired.
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Usually black paint absorbs heat, but painting an object with a black version of this new coating kept it about 16°C cooler than when an object painted with commercial black paint was exposed to the same amount of sunlight.
In another test, the new paint coating was found to be able to maintain its colour despite being placed in an oven at 60°C for 30 days.
Yang says this paint could help save electricity and reduce carbon dioxide emissions.
“Solar reflective and thermally emissive surfaces offer a sustainable way to cool objects under sunlight,” says Mingqing Wang at University College London, who was not involved with the work. This could be useful in tropical locations to help keep buildings cool and reduce electricity consumption from air conditioning, as well as to prevent cars, buses and trains from getting too hot, she says.
An intriguing next step would be to try and add more functionality to the coating, for instance to enable the energy from the reflected infrared light to be harvested to generate electricity, says Wang.
Journal reference: Science Advances, DOI: 10.1126/sciadv.aaz5413
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