Solar power's biggest problem is panels only work when the Sun is shining – but could you turn to the dark side and make panels that work at night? It's theoretically possible, and now one team has done it. The amounts of energy are so tiny its inventors had trouble even measuring them, but they're confident there is plenty of potential to improve.
The Sun emits radiation across a broad part of the electromagnetic spectrum. Photovoltaic panels capture part of the visible and ultraviolet sections of this, turning them into electricity. The light not used in this way warms the Earth and is radiated back into space at night, but at much lower frequencies in the infrared.
With the right material, that infrared radiation can perform the same role as visible light on solar panels, releasing electrons whose flow can power electrical devices.
In the journal ACS Photonics researchers describe making this happen, using the same materials used by night vision goggles to detect infrared radiation.
“Whenever there is a flow of energy, we can convert it between different forms,” Ekins-Daukes said. Co-author Dr Phoebe Pearce added; “We are diverting energy flowing in the infrared from a warm Earth into the cold universe.”
The team is part of the lab responsible for most of the incremental steps that took photovoltaic panels from a laboratory curiosity to the world's largest source of newly installed power in recent years.
Ekins-Daukes admitted to IFLScience that the device described in their paper collects about a hundred-thousandth of the electricity of an equally sized solar panel in direct sunlight. By coincidence, that's similar to the difference in brightness of the full Moon compared to the Sun. Unlike the idea of collecting moonlight with existing solar panels, however, this product has plenty of room to improve.
The researchers calculate it's theoretically possible for photovoltaics capturing night radiation to produce about 10 percent of the electricity of existing panels during the daytime. This might even be enough to compete with storage to power society at night.
Solar panels only reached their existing capacities because they captured niches such as powering satellites and remote facilities, creating a market that brought in funding for mass production and further research. Ekins-Daukes told IFLScience the team hopes to do something similar.
“There's a meter in my house that measures how much hot water I use,” Ekins-Daukes said. “Now and then the battery needs to be replaced. If we could power the meter off the heat of the water, that wouldn't be necessary.” A potentially larger but more distant niche would be clothes that produce electricity from the wearer's body heat. Meanwhile, Ekins-Duakes told IFLScience the existing version could power a wrist-watch; "but not one of the modern multi-function ones".
The team is not the only one seeking to harness nocturnal radiation. Stanford researchers have also achieved preliminary success, but the methods are different. “Their approach is thermal,” Ekins-Daukes told IFLScience. “Heat from the ground flows through a cold surface driving a thermoelectric generator. Ours is a quantum effect, using the radiation to create electricity directly.”
Ekins-Daukes acknowledged the technique is best suited to cloudless locations where the temperature difference between the ground and the night sky is greatest. If you want to fill the gaps in solar production caused by clouds you could go for boring but effective batteries, or turn to speculative technologies that harvest the energy of falling raindrops.