How Reverse Solar Panels Could Generate Power at Night

© Geir Pettersen/Getty   Scientists are developing a new way to turn escaping nighttime heat into "reverse solar"-style energy. Here's how it works.

By Caroline Delbert, Popular Mechanics

• Scientists are developing a new way to turn escaping nighttime heat into "reverse solar"-style energy.

• This isn't the only team to work on capturing low-wavelength radiation as a way to increase energy efficiency.

• The secret is using thermal radiation cells instead of photovoltaic solar cells.

From the annals of symbolism, Inverse reports that scientists are working on backward solar panels that generate power at night. In what could be the most hardcore paper title ever, the researchers are calling their process “Optically Coupling with Deep Space.”

So what does that mean? Well, photovoltaic cells accumulate heat during the day, even during cloudy days. What they register, though, is the visible spectrum of light, which is a different animal. To turn even low-level heat into energy, scientists have to use a thermal cell instead of a photo cell. The materials must be able to absorb the lowest wavelengths of energy.

Researchers are working on projects like individual molecules that harvest the full spectrum of light, but for this project, the team is considering mercury alloys that will absorb the low wavelengths in particular. The mechanism itself will work by just reversing what we think of as the mechanism for solar power.

Photovoltaic cells on Earth collect energy from the sun, partly because the huge radiation of the sun dwarfs the almost zero ambient radiation thrown off by the Earth. In a thermal radiation cell, we reset the parameters so Earth is the new sun, and its even minimal accumulated heat dwarfs the cold, midnight black of outer space. Letting heat seep out of thermal cells at night, drawn out by the cold night sky, could let scientists capture the energy as it goes out the same way we capture the sun’s energy as it comes in.

The overall process is what’s known as a heat sink, where accumulated heat is released somehow. The term could be familiar to people who build or use gaming PCs, but an air- or water-cooled engine is using those fluids as heat sinks, too. You can buy a pizza heat sink to make sure your pie cooks evenly through the middle before the edges get burned, or a special pot that boils things faster.

Deep space is the heat sink in this case, providing the fluid into which accumulated radiant heat is released. The research team says its technology could gather up to 25 percent of what a similar solar cell would accumulate during full daytime light.

The scheme resembles a form of energy recycling where scientists try to recapture escaping low-grade heat made by all kinds of machinery and technology. Plenty of rising alternative energy ideas includes skimming the very highest levels of solar, nuclear reactions, or burning hydrogen.

But low-grade energy can potentially solve problems these more glamorous technologies don’t address, and so can radiant nighttime energy. The more tools we have to harvest renewable energy in the future, the more we can reduce the demand for traditional fossil fuel power plants.