From water-making solar panels to new cleaning methods, scientists are always looking for ways to make solar panels more efficient and useful. Recently, engineers at Stanford University devised a thermoelectric generator that uses the infrared light bouncing from the surface of solar panels to generate a small amount of electricity, essentially creating electricity from the panels even at night. But while the science is sound, it’s the economics that could prevent this from gaining mainstream traction. “I will say that one of the greatest challenges for thermoelectric [applications] is converting low-temperature heat, [because at] near room temperature, the efficiencies are very, very low,” explained Dr. David Ginley, Chief Scientist at the National Renewable Energy Laboratory (NREL) in an email to Lifewire. “In this case, the problem is that the energy content is small, and waiting till night means you lose some of the [energy] through radiation in any case.”
Let There Be Light
Led by Ph.D. candidate Sid Assawaworrarit, the researchers outfitted their thermoelectric generator to a regular solar panel and used the contraption to generate a small amount of electricity from the infrared light escaping from the surface of solar panels at night. A thermoelectric generator produces a small amount of electricity by taking advantage of the slight difference in temperature between the ambient air and the surface of a solar panel when it’s pointed directly into a clear sky. The Sun directs a tremendous amount of energy to the Earth, but barring some of it that’s trapped by the greenhouse gasses, the planet virtually sends out much of the energy it receives in the form of infrared radiation, in a process known as radiative cooling. The process was used in ancient India and Iran to freeze water and create ice and works best on cloudless nights, since clouds reflect infrared light toward the ground. Assawaworrarit and his team have devised a new way to capture that energy as it departs the planet. As the solar panel cools, the escaping photons carry heat, which the researchers capture with their thermoelectric generator to convert into electricity. Scientists first tried capturing infrared light in 2019, and now the Stanford researchers have managed to combine this technology with regular solar panels to make it more accessible and efficient.
Proof of Concept
On a clear night, the device Assawaworrarit tested on the Stanford rooftop generates roughly fifty milliwatts, or 0.05 watts, for every square meter of solar panel. In contrast, solar panels can typically generate about 150 watts per square meter during the day. To put the numbers into perspective, a small LED bulb draws 18 watts of electricity. Fifty milliwatts isn’t a huge number, but the researchers argue the numbers add up when the technology is applied at scale. There are a lot of applications where this kind of energy at night, however minuscule, could come in handy, especially when you consider that a significant amount of the world’s population still doesn’t have access to electricity round the clock. And this is just the start. Assawaworrarit told Interesting Engineering that with a bit of work and in more conducive weather conditions, the researchers could double the amount of electricity generated by their device, adding that the theoretical limit is about one or two watts per square meter. The researchers believe the system could be very attractive from a cost perspective if they can get it to generate up to a watt per square meter. However, there are still some ways to go for the system to achieve that kind of efficiency. As it stands now, Dr. Ginley remains unimpressed. In his opinion, before the technology can be used in the real world, someone will have to do a good energetic analysis combined with an initial tech-to-market assessment. Moreover, he thinks the cost of thermoelectric generators, as compared to their reliability and efficiency, makes them a poor match for use with solar cells. “The cost of the incremental power [gained] in this case is probably not ultimately worth the cost,” opined Dr. Ginley.
