“[Radiative cooling] seemed too good to be true. So why wasn’t it being used? Why did so few people know about it?” AASWATH RAMAN  UCLA assistant professor of materials science and

engineering  Aaswath Raman, a UCLA assistant professor of materials science and engineering, was a graduate student when he stumbled across a handful of papers on radiative cooling — the

process by which heat radiates upward from objects on Earth all the way to the cold depths of outer space. It captured his interest, and he now studies how to harness this movement of heat

for technological gain. Raman’s efforts have earned him a Sloan Research Fellowship, an MRS Nelson “Buck” Robinson Science and Technology Award for Renewable Energy and a spot on _MIT

the importance of energy issues. As I grew older, I became particularly passionate about climate change. I ended up studying physics and computer science, and then I worked at Microsoft for

a little while. I almost had a very different career path in the tech industry. But I decided to go back to school and get a Ph.D. because I really felt that basic, fundamental scientific

research was needed to tackle energy challenges and climate change. When I came across this concept of radiative cooling, it led me on what’s been a very unexpected and interesting path.

Radiative cooling is a natural phenomenon that happens all the time. All materials emit light and heat corresponding to their temperature. You can’t see this light with your naked eye, but

when you look [at something] through a thermal infrared camera, that [light] is what you’re seeing. At night, objects facing the sky send this infrared light and heat upward. Some of it

bounces off greenhouse gases in the atmosphere and comes back down, but some of it escapes out to space. Because some of the heat is lost, objects facing a clear night sky can actually cool

down to below the air temperature. Seeing radiative cooling in action is as simple as going outside on a cloudless night and measuring the temperature of your roof or observing frost on the

ground, even when the air temperature hasn’t quite dipped below freezing. It seemed too good to be true — it’s free cooling, and all you have to do is put something outside [that faces] the

sky. So why wasn’t it being used? Why did so few people know about it? It seemed like an interesting opportunity to ask questions about whether this could be used to drive cooling

technologies. The first big puzzle was figuring out how you can make use of this effect when we need cooling the most — during the daytime. Historically, radiative cooling was called “night

sky cooling,” because that’s when we notice the effect. During the day, the sun tends to heat up almost every natural material enough to completely counteract radiative cooling. That’s where

materials engineering comes in. I realized that we could engineer an artificial material that has a special set of optical properties. I designed a material that reflects sunlight, so it

doesn’t heat up during the day, and at the same time, it also very effectively emits heat through radiative cooling. This means it’s able to stay cooled to below the air temperature, even in

the middle of the day when the sun is shining on it. The immediate application is to cool the air for air-conditioning and refrigeration systems. I launched a company, SkyCool Systems, to

pursue this commercially. They’ve already launched three pilot studies in Northern California, and it’s moving forward quite well. I’m a chief scientific officer now and not involved in the

day-to-day operations, but it’s been really neat to watch it grow. Just a few years ago, this was a lab experiment, and now it’s out there as an actual technology. We wanted to do something

else with radiative cooling, and the other big thing that came to my mind was that we should be able to generate some electricity at night, when we can’t generate solar power. This time, we

didn’t need to engineer any new kind of material. We used a device called a thermoelectric generator — which converts differences in heat to electricity — and paired it with a black aluminum

disc. As the disc radiated heat, the generator captured that temperature difference to produce energy. Not very much yet! We showed that we could keep one LED lightbulb on. But I think it

could be useful in any scenario where you don’t have access to the sun for solar power. In polar regions, for instance, you could power sensors or small lights for decades without worrying

about having to replace the battery. But we’re also looking at ways of improving and scaling up the technology to generate more energy. In general, we need more investment in both basic and

applied research when it comes to energy and climate-related challenges. In reality, no one solution is going to solve every aspect of the energy challenges we face. People focus a lot —

rightly so — on renewables and solar, and I’m a huge advocate of them. But I think talking about [how to] efficiently use electricity — especially when running appliances — is equally

valuable, because that reduces the demand for electricity to begin with. Air conditioning and refrigeration are a sizable chunk of our energy use, and therefore our carbon emissions. If

radiative cooling could help reduce the amount of energy used by these systems, that could make a huge difference. I hope what gets conveyed by all this is a sense of optimism. People tend

to get pessimistic and concerned by everything they hear about climate change and the perceived lack of progress on the energy front. And while the stuff I work on is by no means going to

solve it, it’s a great example of how there are still possibilities for unexpected and creative solutions out there.