A new cooling structure designed by a Stanford research team can cool structures even under direct sunlight, according to a profile of the device in Nano Letters.
The device is highly reflective, keeping it from heating up and defeating the purpose of cooling. It also uses the same mechanism as the greenhouse effect to direct thermal radiation away from itself – specifically, it efficiently emits thermal radiation within a tightly defined wavelength range that can escape through the atmosphere. Light outside that range is reflected back to the earth, trapping heat and raising the temperature below.
Previous studies focused on using radiative cooling at night to mitigate the greenhouse effect. However, peak cooling demand occurs in the daytime, which posed considerable challenges for previous researchers.
"We've taken a very different approach compared to previous efforts in this field," said Aaswath Raman, a doctoral candidate in Fan's lab and a co-first-author of the paper. "We combine the thermal emitter and solar reflector into one device, making it both higher performance and much more robust and practically relevant. In particular, we're very excited because this design makes viable both industrial-scale and off-grid applications."
The device achieves a net cooling power of over 100 watts per square meter, roughly the same amount of power generated by the average commercially available solar panel. The passive technology requires no energy to operate and could someday replace existing solar panels that feed electricity to HVAC systems, the research team says.