The new metamaterial (meaning, artificially created) was developed by engineers from the University of Colorado, Boulder and the University of Wyoming, Laramie. It’s as thin as an aluminum foil, looks like a roll of plastic wrap, and can function as a natural airconditioner. When the material is applied to a surface, it cools the object beneath it by reflecting sunlight back to space while simultaneously allowing the surface to cool itself by naturally discarding its own heat through infrared radiation — a process known as passive radiative cooling.
While natural night-time cooling can be achieved through thermal radiation (reflecting of incoming sunlight back to the atmosphere), natural daytime cooling isn’t as easy. The reason for this is that when a structure is exposed directly to sunlight, the heat it loses through passive radiation can easily be offset by absorbing even just a little bit of sunlight.
This is the challenge that was taken on by the team. Basically, they wanted to figure out a way to simultaneously take advantage of thermal radiation and passive radiation. Their solution was to create a specially-designed material that can do exactly that.
First, they embedded visibly-scattering but infrared-radiant glass microbeads into a polymer film. Then to achieve maximum reflecting capability, they added a thin silver coating underneath the film.
When they tested their newly created metamaterial, it demonstrated a cooling effect that was equivalent to around 110 watts per square meter over a 72-hour duration, and over 90 watts per square meter under direct sunlight during high noon. That cooling power isn’t simply comparable to what solar cells can typically generate for an area of the same size. Even better, the cooling power provided by their metamaterial can be achieved regardless of what time it is. In other words, its effect will be the same whether it’s morning, noon or night.
As stated in a press release issued by the team, the material ‘could provide an eco-friendly means of supplementary cooling for thermoelectric power plants which currently require large amounts of water and electricity to maintain the operating temperatures of their machinery.’ One of the authors of the research was also quoted as saying that 10 – 20 square meters of the material placed on the rooftop of a single-family home will be adequate enough to cool the entire house during the summer.
Aside from electricity-less cooling of buildings and power plants, the metamaterial can also be used to improve the operating efficiency of solar panels by keeping them from overheating, thereby allowing them to work harder, longer.
In conclusion, Ronggui Yang (one of the study authors) said: “The key advantage of this technology is that it works 24/7 with no electricity or water usage. We’re excited about the opportunity to explore potential uses in the power industry, aerospace, agriculture and more.”
Details of the research can be viewed through the journal ‘Science’ under the title “Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling”.
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