Published on March 28th, 2013 | by James Ayre1
New Solar Structure Vastly Improves The Daylight Cooling Of Buildings
A completely new type of cooling panel capable of vastly outperforming previous forms has been created by researchers at Stanford University. The new structure works to radiate significant amounts of sunlight back into space even in full sunlight.
To explain the breakthrough in specific terms: “a typical one-story, single-family house with just 10 percent of its roof covered by radiative cooling panels could offset 35 percent its entire air conditioning needs during the hottest hours of the summer.”
Can you imagine homes and buildings cooled significantly without the use of air conditioners? It’s a compelling thought.
As the press release from Stanford University’s Engineering site states it, “Tapping the frigid expanses of outer space to cool the planet. Science fiction, you say? Well, maybe not any more.”
“People usually see space as a source of heat from the sun, but away from the sun outer space is really a cold, cold place,” says Shanhui Fan, professor of electrical engineering and the paper’s senior author. “We’ve developed a new type of structure that reflects the vast majority of sunlight, while at the same time it sends heat into that coldness, which cools humanmade structures even in the day time.”
The engineering “trick” that makes this possible is the crossing of an important thresh-hold. The reflector needs to be effective enough that it absorbs only a very low minimum of sunlight, and avoids heating up at all as a result.
The other important factor is that the structure needs to be very efficient at radiating heat back into outer space. “Thus, the structure must emit thermal radiation very efficiently within a specific wavelength range in which the atmosphere is nearly transparent. Outside this range, Earth’s atmosphere simply reflects the light back down.” You’re probably already familiar with this effect, it’s commonly known as the greenhouse effect.
The new cooling panel, made from nano-structured quartz and silicon carbide, fulfills both of these requirements. It’s very effective at reflecting most sunlight, while also very effectively emitting thermal radiation in the wavelength range necessary to escape the Earth’s atmosphere.
“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 specifics of the device are detailed in a paper published in the journal Nano Letters.