Do Solar Panels Work At Night?

With the latest energy crisis, it should come as no surprise that renewables are making headlines once more. This time it’s solar panels with a thermoelectric generator that can generate small amounts of electricity at night!

Generating Solar Energy At Night

Researcher Sid Assawaworrarit and his colleagues in Stanford, California have invented solar panels that can work at night. However, for best results, the sky needs to be clear as that means infrared light from the surface of these solar panels can radiate into space.

Assaworrarit and his colleagues fitted ordinary solar panels with a thermoelectric generator that creates a small amount of electricity. This comes from the slight difference in temperature between the ambient air and the surface of the solar panel pointed into space. While light from the Sun hits the solar cell during the day, it does the exact opposite at night, i.e. emits infrared radiation.

“There’s actually light going out [from the solar panel], and we use that to generate electricity at night. The photons going out into the night sky actually cool down the solar cell,” says Assaworrarit.

How Do These Solar Panels Work?

The photons leaving the surface of the solar panel carry heat along with them. That means when there are no clouds to reflect infrared light back toward Earth, the surface of these innovative solar panels is a few degrees cooler than the air around it.

By using a thermoelectric generator, Assawaworrarit and his colleagues could capture some of the heat flowing from the warmer air to the cooler solar panel which converts it into electricity. They tested the device on a clear night on Stanford rooftops and generated approximately 50 milliwatts for every square metre of a solar panel (50 mW/m2).

The theoretical limit is probably about one or two watts per square metre. That’s not a huge number, but there are a lot of applications where that kind of energy at night would come in handy. This radiative cooling may reduce the need for expensive batteries in certain applications.

Possible Applications For Night-Time Solar Panels

Considering one billion people across the world are without access to a reliable electrical grid, these new solar panels could provide possible solutions. While people in these areas can rely on solar power during the day, they are limited in terms of generating power at night.

Unlike lithium-ion and other batteries that degrade after a few thousand charge cycles, the thermoelectric generators used in these new solar panels are solid state. That means “the lifetime is pretty much forever,” according to Assawaworrarit.

Another potential application is to power the tremendous network of environmental sensors that researchers use. From keeping tabs on weather conditions to invasive species across the globe, solar panels that can generate a small amount of electricity at night could greatly reduce the need for batteries and the subsequent maintenance and replacement costs.

Using The Earth And The Sun As An Energy Source

The Earth constantly receives an immense amount of energy from the Sun, approximately 173,000 terawatts or 173 trillion watts. Of the energy we receive, clouds, particles in the atmosphere and reflective surfaces like snow-covered mountains reflect 30% back into space. The rest warms the land, oceans, clouds, atmosphere and everything else on Earth.

Except for the additional heat from greenhouse gasses, that energy doesn’t stay here. In fact, the Earth sends out almost as much energy as it receives in the form of infrared radiation. The heat from the planet glows with wavelengths that are too long for the human eye to detect, but it does carry energy. In reality, more than half of the total solar energy that reaches the Earth goes through this process, eventually returning to space.

Innovations In Solar Panels

While Assawaworrarit and his colleagues have discovered a new way to capture energy as it leaves Earth, there have been similar projects using a thermoelectric generator. The first to capture this kind of energy was in 2019. Researchers at UCLA utilised the principles of radiative sky cooling to develop a novel method for generating renewable energy at night.

Using this cutting-edge technology and solar panels that generate power during the day, Assawaworrarit and other researchers have made a significant stride toward making it accessible to everyone.

While it’s already a tremendous breakthrough, the team is not stopping there. They are planning on making a few improvements and also placing this device in an even better location where it could generate twice the amount of electricity.

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