A new device can produce electricity using shadows

Someday, shadows
and light could team up to provide power.

A new device
exploits the contrast between bright spots and shade to create a current that
can power small electronics. “We can harvest energy anywhere on Earth, not just
open spaces,” says Swee Ching Tan, a materials scientist at the National
University of Singapore.

Tan and his
team created the device, called a shadow-effect energy generator, by placing a superthin coating of
gold on silicon, a typical solar cell material. Like in a solar cell, light
shining on silicon energizes its electrons. With the gold layer, the
shadow-effect energy generator produces an electric current when part of the
device lies in shadow.

The excited
electrons jump from the silicon to the gold. With part of the device shaded, the
voltage of the illuminated metal
increases
relative
to the dark area and electrons in the generator flow from high to low voltage.
Sending them through an external circuit creates a current that can power a
gadget
, Tan’s team
reports April 15 in Energy & Environmental
Science
.

With eight
generators, the team ran an electronic watch in low light. The devices can also
serve as sensors.  When a
remote-controlled car passed by, its shadow fell on a generator, creating the
electricity to light up an LED.

The greater
the contrast between light and dark, the more energy the generator provides. So
the team is working to boost the device’s performance by borrowing strategies from
solar cells for gathering light. Increasing the light these generators absorb
would allow them to better exploit shadows.

Someday, these generators might produce energy in the shadowy spots in a solar array, between skyscrapers or even indoors. “A lot of people think that shadows are useless,” Tan says. But “anything can be useful, even shadows.”

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