Nearly one billion citizens worldwide can’t access electricity during the night because the solar panels many of them rely on don’t generate power in the dark. One solution is to store up excess daytime energy so it can be used when it is needed but this requires serious amounts of battery storage.
These intermittency and battery issues have been eliminated by a Stanford University research team that has pioneered a photovoltaic cell capable of harvesting energy at night, as well as during the day. Details of the new device, which works by harnessing the heat that moves from the Earth into space overnight – energy on a par with incoming solar radiation, were published today in the journal Applied Physics Letters.
The Stanford device, which can be setup cheaply within current solar cells, ‘uses a thermoelectric module to generate voltage and current from the temperature gradient between the cell and the air’ in a process that ‘depends on the thermal design of the system, which includes a hot side and a cold side’.
“You want the thermoelectric to have very good contact with both the cold side, which is the solar cell, and the hot side, which is the ambient environment,” said author Sid Assawaworrarit. “If you don’t have that, you’re not going to get much power out of it.”
Only a few watts of power are needed to provide electricity at night and the initial prototype, which the researchers have successfully demonstrated can work at night, generates 50 milliwatts per square meter. Which means ‘lighting would require about 20 square meters of photovoltaic area’.
“None of these components were specifically engineered for this purpose,” added author Shanhui Fan. “So, I think there’s room for improvement, in the sense that, if one really engineered each of these components for our purpose, I think the performance could be better.”
The team are now focused on making engineering improvements to enhance the performance of the device.