Night-time solar panels developed at Stanford
It probably goes without saying, but of all the energy solar panels generated last year, none were produced at night. New research shows that this doesn’t have to be the case.
Stanford researchers have modified commercially available solar panels to generate a small amount of electricity at night by harnessing a process known as radiative cooling, which relies, no doubt, on the freezing vacuum of space. . The research was published in early April in Applied Letters in Physics.
“We tend to think of the sun as an important renewable energy resource,” said Shanhui Fan, the project’s lead researcher. “The coldness of outer space is also an extremely important renewable energy resource.”
While the modified panels generate a tiny amount of power compared to what a modern solar panel does during the day, that power could still be useful, especially at night when power demand is much lower, said Researchers.
Technically speaking, modified solar panels do not generate solar electricity at night. Instead of harnessing sunlight (or starlight or moonlight, which still doesn’t work), the researchers added technology that harnesses radiative cooling.
When an object faces the sky at night, it radiates heat out into space, which means an object can become colder than the temperature of the air around it. This effect could have obvious applications in cooling buildings, but the temperature difference can also be used to generate electricity.
Fan, an electrical engineering professor, and his fellow researchers added technology to a commercial solar panel that could do just that and was able to generate a small amount of electricity at night.
The modified panel generated 50 milliwatts per square meter at night. Although this is far more than previous versions of this technology, it is well below what a commercial solar panel can produce during the day. A bottom-of-the-envelope calculation gives nearly 200 watts per square meter for a commercial solar panel. One watt equals one thousand milliwatts.
“So it’s significantly lower,” Fan said. “But it can potentially be useful for some of the low power density applications.” That could include nighttime lighting, charging devices and keeping sensors and monitoring equipment online, Fan said.
Fan says the changes were made to commercial solar panels, meaning the technology could be widely deployed. He also said that by improving the design, more electricity could be generated.
There are still many questions that need to be answered before a commercial application can be deployed, Geoff Smith, emeritus professor of applied physics at the University of Technology Sydney, wrote in an email response to questions. Smith, who was aware of the research but did not participate in it, doubts it will ever be an economically viable source of energy.
“Adding complexity and degradation pathways to renewable energy systems, while interesting scientifically, rarely makes it practical,” he wrote.
The research proves you can generate electricity this way and was not meant to prove anything about future practical applications, Fan said.
Still, Smith agrees that more attention should be paid to outer space as a source of renewable energy. In his view, cooling and other modes of power generation hold more promise, but that the night sky is a valuable avenue for shifting energy use.
Although it does not yet produce much electricity, radiative cooling is almost ubiquitous.
“Whenever you’re outside, you actually do it,” Fan said.