The electrical engineer Sid Assawaworrarit, leading a team of researchers from Standford University (USA), has developed a device that allows photovoltaic electricity to be generated at night. This is an ordinary solar panel equipped with a thermoelectric generatorwhich generates a small amount of electricity from the slight difference in temperature between the ambient air and the surface of a solar panel pointed out into space.
The new technology takes advantage of a surprising fact about solar panels. During the day, there is a light that comes from the Sun and hits the solar cell, but during the night the reverse happens. This is because solar panels, like anything hotter than absolute zero, emit infrared radiation.
“Actually, there is light coming out of the solar panel, and we use it to generate electricity at night. The photons going out into the night sky actually cool down the solar cell,” says the head of the team of scientists.
As those photons leave the solar panel’s surface toward the sky, they drag heat with them. This means that on a clear night, when there are no clouds to reflect infrared light back to Earth, the surface of a solar panel will be a few degrees cooler than the surrounding air.
Assawaworrarit and his colleagues take advantage of this temperature difference. A device called a thermoelectric generator can capture some of the heat flowing from the warmer air to the cooler solar panel and convert it into electricity.
On a clear night, the device Assaworrarit tested on the roof of Stanford generates about fifty milliwatts for each square meter of solar panel (50 mW/m2).
The engineer claims that with a couple of improvements, and in a good location, such a device could generate twice that amount of electricity.
“The theoretical limit is probably one or two watts per square meter. It’s not a huge number, but there are many applications where that kind of power at night would be very useful, “he says.
The type of thermoelectric generators used in these solar panels are solid state, so their useful life is practically eternal.
One use of this technology is to power the vast network of environmental sensors that researchers use to monitor everything from weather conditions to invasive species in remote corners of the planet. Again, solar panels that generate a small amount of electricity at night could reduce the need for batteriesand the associated maintenance and replacement costs.
If you can get to one watt per square meter, that would be very attractive from a cost point of view.
An easily overlooked power source
The Earth constantly receives an enormous amount of energy from the Sun, on the order of 173,000 TW. Clouds, particles in the atmosphere, and reflective surfaces such as snowy mountains immediately reflect 30% of that energy back into space. The rest ends up heating the land, the oceans, the clouds, the atmosphere and everything else on the planet.
But that energy does not stay here. Except for the additional heat that greenhouse gases have been trapping since humans began burning copious amounts of fossil fuels since the Industrial Revolution, the Earth sends out as much energy as it receives. So the planet emits a truly mind-boggling amount of energy in the form of infrared radiation.
“It’s a kind of light. The infrared radiation that shines off the warm Earth (or anything else) has wavelengths too long for our eyes to see, but it carries energy. In fact, more than half of the amount total solar energy that reaches the Earth goes through this process, to end up returning to space”, indicates the engineer.
What Assawaworrarit and his colleagues have done is a new way to capture that energy as it leaves the planet.. They are not the first to use a thermoelectric generator to capture this type of energy. By integrating this new technology with solar panels that generate electricity during the day, the researchers have taken an important step toward enabling ordinary people to capture this energy for themselves.
Reference article: https://ecoinventos.com/stanford-panel-solar-genera-electricidad-por-la-noche/