Radiative sky cooling is a phenomenon that sees frost form on the ground when temperatures are still above freezing. It accounts for water droplets forming on car windshields and frost on the grass at night.
Now, it's been harnessed to create a technology that could be the night time twin of solar energy.
Renewable night energy
Researchers, led by a UCLA materials scientist, say they have leveraged the principles behind radiative sky cooling, and have created an innovative solution for producing renewable energy at night.
In a paper published in the journal Joule, they outline the low-cost technology that could eventually help more than 1 billion people worldwide who lack reliable access to electricity, according to the International Energy Agency.
The tech concept described in the paper, titled Generating Light from Darkness, could be used as a standalone solution or could work with solar energy allowing for electricity to be generated at all hours from the same location.
Radiative sky cooling
The phenomenon underlying the new technology, radiative sky cooling, is a natural occurrence in which a surface facing the sky ejects its heat into the air in the form of thermal radiation. Some of that heat rises to the upper atmosphere and can even go into space.
“This effect occurs naturally all the time, especially on clear nights,” Aaswath Raman, leader of the study, and an assistant professor of materials science and engineering at the UCLA Samueli School of Engineering said in a press release.
“The result is that the object ejecting the heat, whether it’s a car, the ground or a building, will be slightly cooler than the ambient temperature.”
The new technology uses that difference in temperatures to generate electricity. The scientists created a device that could capture rising heat from the surrounding air and convert it into electricity.
An inexpensive solution
The device that was created was able to power an LED bulb.
All of the parts used for the experimental device were bought at hardware and electronic supply stores, all at a total cost of less than $30.
The setup included an aluminum disk, painted black on one side, which was placed to face the sky. The disk was used to radiate the heat from the surrounding air. It also included a thermoelectric generator — a device that generates an electric voltage in response to temperature differences.
The device generated approximately 25 milliwatts per square meter. While this is much less than a similarly sized solar cell, Raman said the device could be easily be used to generate power in locations that are off the electrical grid.
Raman and his team are working on improving the technology by creating more powerful prototypes.