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Whoa: This Generator Turns Shadows Into Electricity

Courtney Linder
Photo credit: Royal Society of Chemistry

From Popular Mechanics

  • Researchers at the National University of Singapore have come up with a new way to harvest energy: creating electricity out of shadows.
  • The so-called "shadow-effect energy generator" produces an electric current when part of the device lies in shadows, just as the name suggests.
  • They published their findings in the journal Energy & Environmental Science.

When you consider the solar panel, you likely conjure images of vast open fields, covered in rows upon rows of solar cells, harvesting precious energy from the sun. But what if we could shift that paradigm between passive green energy and the sun?

That's what scientists from the National University of Singapore have set out to do. They've devised a "shadow-effect energy generator" that quite literally turns darkness into light, meaning we could collect energy in even the tightest spaces, from a windowsill to that patch of grass in your background that only sees partial sunlight.

To do this, the generator "scavenges the illumination contrast that arises on the device from shadow castings, and generates a direct current, simply by placing a part of the generator in shadow," the researchers write in their paper, which appears in the journal Energy & Environmental Science.

Traditional solar panels do technically work in the shadows, but they'll only achieve about half as much energy as their counterparts in full sunlight, since the light is indirect. This is common to households that may be partially shaded by tall trees, for example. But for this reason, the paper's authors say engineers have "strenuously avoided" shadows in optoelectronic applications. Until now.

Inside the shadow-effect energy generator, there's a silicon wafer—the usual substrate for solar cells—with an ultra-thin gold coating that's only 15 nanometers thick. (For reference, a strand of human DNA is only about 2.5 nanometers thick.) When light meets the silicon, photons, or light particles, knock electrons free from their atoms, which creates an energy flow.

This is exactly the same process your average solar cell follows, but the gold layer is the true standout. With that gold coating, the device can bring about a stronger electric current when the device is partially obscured in shadow—200 percent better than ordinary solar cells, to be exact. As the agitated electrons jump from the silicon to the gold layer, the metal's voltage increases when there's a difference between the light and dark portions.

Using eight of these generators, the team actually powered an 1.2-Volt electronic watch in ambient light. In another test, a remote-controlled toy car drove past the device, creating a shadow and subsequently powering up an LED. For that reason, the scientists believe their generator would be suitable for powering low-energy sensors attached to buildings, as part of a "smart city" concept. They could even usher in urban solar farms that could harvest energy between massive skyscrapers that cast long shadows.

Moving forward, the researchers want to integrate more solar cell technology into their device so it can better harvest small amounts of light. They're also looking at ways to embed the small generators into clothing as a smart textile so we can collect energy on the go.

It'll be a while before we see anything like this hit the commercial market, though, so in the meantime, make sure your solar panels are installed on the sunniest part of your roof or yard.

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