Writer: H M Remi

As the name implies, solar panels generate electricity with the power from the sun. Thus, solar panels are useless in the darkness of night when the sun is absent. Yet, a team of Californian electrical engineers has found a way to enable solar panels to generate electricity at night. By attaching thermoelectric generators to the ordinary solar panels, the blue panels can radiate infrared light out to space and generate electricity if the night sky is cloudlessly clear.

The secret behind this new technology is simply physical: everything warmer than absolute zero emits infrared radiation.
 
During the daytime, the solar cells on the solar panels absorb sunlight to generate power. It reverses when night falls. The solar panels are no longer “absorbers” but “emitters”. Not just emitting photons and heat,  they also emit infrared light to the night sky. If the sky is clear with no clouds to reflect infrared light back to Earth, the solar panels would be a few degrees cooler than the air around them when cooling down. Then, the thermoelectric generator will capture the heat from the air around and convert heat into electricity. Roughly, every square meter of solar panels can generate 50 milliwatts of power.
 
The engineers also resolved the problem of solar panels being poor heat conductors. Thermal energy does not transmit efficiently in solar cells. Therefore, the heat “escaping” from the solar panels' edges did not contribute much to the power generation. But, by attaching an aluminum plate directly to the solar cell, the energy conduction efficiency can be increased drastically. It lets the thermoelectric generators and solar panels work together to generate electricity at night.

Roughly a billion people are living outside electrical grids around the globe. Although solar panels can generate electricity during the day, they are not quite helpful at night. The residents outside the electrical grid can only count on batteries for electricity after sunset. But batteries would degrade after a few thousand charge cycles and thus cause problems against environmental sustainability. Working with solar panels, the innovative thermoelectric generators will be a good starting point for solving problems for people and nature.

Source: 
https://interestingengineering.com/stanford-solar-panel-night

Image source: 
https://interestingengineering.com/stanford-solar-panel-night