Professor Shanhui Fan's rooftop cooling system could eventually help meet the need for nighttime lighting in urban areas, or provide lighting in developing countries.

Using commercially available technology, the research team has designed an off-grid, low-cost modular energy source that can efficiently produce power at night.

Although solar power brings many benefits, its use depends heavily on the distribution of sunlight, which can be limited in many locations and is completely unavailable at night. Systems that store energy produced during the day are typically expensive, thus driving up the cost of using solar power.

To find a less-expensive alternative, researchers led by professor Shanhui Fan looked to radiative cooling. Their approach uses the temperature difference resulting from heat absorbed from the surrounding air and the radiant cooling effect of cold space to generate electricity.

In The Optical Society (OSA) journal Optics Express, the researchers theoretically demonstrate an optimized radiative cooling approach that can generate 2.2 Watts per square meter with a rooftop device that doesn't require a battery or any external energy. This is about 120 times the amount of energy that has been experimentally demonstrated and enough to power modular sensors such as ones used in security or environmental applications.

"We are working to develop high-performance, sustainable lighting generation that can provide everyone–including those in developing and rural areas–access to reliable and sustainable low cost lighting energy sources," said Lingling Fan, EE PhD candidate and first author of the paper. "A modular energy source could also power off-grid sensors used in a variety of applications and be used to convert waste heat from automobiles into usable power."

Additional authors include Wei Li (EE PhD candidate), and post-doctoral researcher Weiliang Jin, PhD, and Meir Orenstein (Technion-Israel Institute of Technology).

Excerpted from Science Daily, "Efficient low-cost system for producing power at night".