There are different kinds of solar panels. The one most typically used is a type that generates electricity from the sun through a physical process called the photo-voltaic (PV) effect – when light exposure on certain materials generates an electric current. Another type generates electricity from heat through thermal processes – when the sun is hotter and Earth is cooler, and the difference in temperature can be converted into usable energy.
That second kind of solar panel is the one that inspired a team of researchers at Stanford University in Palo Alto, California to develop a new system that can harness energy in darkness. It’s based on the concept of using heat to generate energy but an inverse version of the solar panel. While the solar panel uses the heat difference between the sun and Earth with the Earth being the cooler side – their system makes use of the heat difference between the coolness of the night atmosphere and the Earth with the Earth being the hotter side. The study has been published in the scientific journal Joule.
Study author Shanhui Fan, Stanford electrical engineering professor, told Gizmodo:
The amount of power coming in from the Sun has to be approximately equal to the amount going out from the Earth as thermal radiation, in order to keep the Earth at a roughly constant temperature. The amount of power available for harvesting is very large.
Dubbed an “anti-solar panel” by some, the device has the potential to bridge the gap left by solar energy, collecting energy from the night sky. The thermoelectric generator-based device harnesses the variance in temperature between Earth and outer space by using “a passive cooling mechanism known as radiative sky cooling to maintain the cold side of a thermoelectric generator several degrees below ambient.”
The researchers write:
We use a passive cooling mechanism known as radiative sky cooling to maintain the cold side of a thermoelectric generator several degrees below ambient. The surrounding air heats the warm side of the thermoelectric generator, with the ensuing temperature difference converted into usable electricity. We highlight pathways to improving performance from a demonstrated 25 mW/m2 to 0.5 W/m2. Finally, we demonstrate that even with the low-cost implementation demonstration here, enough power is produced to light a LED: generating light from darkness.
The researchers have only tested their system with a very small prototype. The device was a 20-centimeter (8-inch) aluminum disk painted black and hooked up to commercial thermoelectricity generators. It successfully created enough energy to power a single small LED lightbulb–a small success with immeasurably massive potential. It’s even possible that the device could act in reverse during the daytime, absorbing sunlight and producing electricity from a heat travelling from the sun to the disk and into the outside environment.
As ScienceNews reports:
A bigger version of this nighttime generator could someday light rooms, charge phones or power other electronics in remote or low-resource areas that lack electricity at night when solar panels don’t work.
For now, this device doesn’t come close to the energy harvesting abilities of a solar panel but the technology is still only in the research and development stage. The researchers have already planned improvements including enhanced insulation around the top plate that could potentially raise the device’s energy production to 0.5 watts per square meter or more, and this is only the beginning.
Once they are able to refine the system to produce anywhere close to as much energy as a standard solar panel, it could completely transform the renewable energy sector. It’s cheaper to make and can provide a way to generate electricity at a time that solar panels can’t.