In 2024, scientists built a window that kept a model house about 7°C cooler, without electricity or blocking the view

American families pay an awful lot of their electricity bills every summer battling the heat that some glass panes just let right through. Engineers from South Korea believe that they have managed to develop a solution to this problem, and it does not include overworking the air conditioner, but rather, using another window.

As per a 2024 study titled “Energy-saving window for versatile multimode of radiative cooling, energy harvesting, and defrosting functionalities,” published in the journal Nano Energy, a team of researchers from Seoul National University, led by Professor Seung Hwan Ko, created a so-called "smart window" that in tests, stayed up to 7°C colder than regular glass under direct sunshine without using any energy source. But that is not the only advantage of this window. The design also allows it to generate some electricity when rain falls on it, and it can defog and defrost itself on demand. So, one window, three features, and no external power needed to cool. It seems like the kind of invention that could be useful in glass-fronted buildings in many cities. However, it is not, and there is a pretty good reason for it.

How does glass out-cool your AC unit?


The secret is not a new discovery but rather an ingenious application of existing physics. The window itself consists of a thin layer of fluoropolymer film, which is coated on each side with ultrathin layers of silver and indium tin oxide, the conductive material found in touch screens. This composite layer serves two purposes: it allows visible light to pass through and keeps your view unobstructed, while at the same time reflecting most of the near-infrared light, which otherwise causes heating in a room. At the same time, it also radiates heat outward in the form of infrared radiation within a very specific range of frequency that can pass through the Earth’s atmosphere into the frigid emptiness of space.

A 2014 paper titled "Passive radiative cooling below ambient air temperature under direct sunlight," published in the journal Nature, showed that this technique, known as passive daytime radiative cooling, could cool objects below their surrounding temperature in full sunlight without any power input. The team from Seoul National University took this established discovery and turned it into an actual window that can serve as both a device for looking out and charging your phone in a thunderstorm as well as defrosting the windshield in winter.

Why this actually matters for your wallet

It's not just a neat little demonstration for anyone interested in infrared spectroscopy. The U.S. Energy Information Administration report states that air conditioning uses roughly 19 percent of the total electricity consumed by Americans in their homes and that around 90 percent of American families have at least some type of AC system installed.

The technology was developed and tested in South Korea, but the problem it addresses- high home cooling costs- is a global one, including in the United States. This small invention could potentially affect home energy use. But the part you must keep in mind is that we're talking about a prototype designed for use in an experiment conducted in an outdoor environment rather than a commercial item available at a hardware store.

While 7 degrees was the best recorded figure, the average is much closer to 5 degrees, which can certainly be less impressive. Manufacturing a multilayer optical film at scale, ensuring its durability against hail, pollen, and extreme summer heat, and keeping its price on par with regular double-pane glass is a totally different challenge, and one that isn't yet solved. None of that detracts from the credibility of the research or renders it over-hyped; the authors, thankfully, were specific about the numbers rather than making broad claims. A more cautious takeaway is that windows like this may become more practical over time.