Engineers Create Night-Time Solar Panels That Use Energy Destined for Space

Engineers have designed a type of solar panel that can produce electricity at night, solving one of the key pitfalls of solar power.

Solar power is a promising source of renewable energy. The amount of sunlight that hits the Earth's surface in just one hour and a half is enough to handle the entire planet's energy consumption for a whole year, according to the U.S. Solar Energy Technologies Office.

One of the difficulties of solar power is trying to harness this energy. The other problem is how to keep it going when the sun goes down. Solar panels work by using photovoltaic (PV) cells to absorb energy from sunlight and turn it into electrical current.

One solution to the night-time problem is to store the sun's energy so that it can be used when the sun's not there—but many attempts at this have been problematic. Batteries, for instance, have problems with efficiency and are expensive to use.

Solar panels
A photo shows a solar farm in La Colle des Mees, south-eastern France, in April, 2019. Storing solar power at night has been a hurdle for the technology. Gerard Julien/AFP/Getty

Producing Energy Without the Sun

Another solution is to build solar panels so that they can keep producing energy even when the sun's gone down. A team of researchers think they have done just that.

Their proposed model works by generating electricity from the temperature difference between the PV cells of a solar panel and the surrounding air.

This is possible because whenever heat flows from a hot source to a cold sink, it generates energy. All the time, there is a constant outflow of radiative heat from Earth to outer space since Earth's atmosphere is not able to keep it all in. This is also true for any objects that have access to the sky, the researchers say.

Due to the materials PV cells are made from, at night they end up a few degrees colder than the ambient air since they radiate heat well.

Researchers think this temperature difference might be the key to producing steady power even at night, with the solar panel essentially switching into reverse mode.

Their design is currently capable of producing 50 milliwatts per square meter—not a lot considering lighting usually requires a few watts. You'd need about 20 square meters of photovoltaic area to power some lights with their design currently, according to an American Institute of Physics press release. But there's definitely room for improvement.

"None of these components were specifically engineered for this purpose," author Shanhui Fan said in the press release. "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."

Zunaid Omair, another author behind the work, said in the same statement: "What we managed to do here is build the whole thing from off-the-shelf components, have a very good thermal contact, and the most expensive thing in the whole setup was the thermoelectric itself."

A study outlining the research was published in the journal Applied Physics Letters on April 5, 2022.