Feb 7, 2020: The water drop generator: Electricity from water drops: A newly invented drop
generator generates usable electricity from even the
smallest amounts of water (orig. German: Elektrischer Strom aus Wassertropfen:
Neuartiger Tropfen-Generator erzeugt nutzbaren Strom
schon aus kleinsten Wassermengen)
https://www.scinexx.de/news/energie/elektrischer-strom-aus-wassertropfen/
Translation by Deepl:
<Nadja Podbregar
Small but mighty: researchers have constructed a
system that generates electricity from falling drops
of water. Just one drop is enough to light up 100
small LEDs. This is made possible by a combination of
Teflon, the semiconductor indium tin oxide and an
aluminum electrode. When a drop hits this ensemble, an
electric current is generated. This opens up
completely new possibilities for generating
electricity, the researchers report in the scientific
journal Nature.
Electrical energy can be generated from water - as
demonstrated by hydroelectric power plants at dams,
run-of-river power plants or tidal power plants. Water
can also be used to store energy. However, all these
systems require larger quantities of water to operate
efficiently. The situation is different for test systems
based on the triboelectric effect: In these, the mere
contact of certain materials with water causes an
electrostatic charge and thus generates electricity -
albeit in very small quantities.
Teflon, a semiconductor and a few
pieces of aluminum
But there is another way: Researchers led by Zuankai
Wang of the City University of Hong Kong have now
developed a generator that produces electrical current
from individual drops of water - and does so a thousand
times more efficiently than previous approaches of this
kind. Similar to triboelectric systems, their droplet
generator relies on the interaction of water droplets
with certain materials.
The device consists of a layer of the semiconductor
indium tin oxide (ITO) to which is applied the polymer
polytetrafluoroethylene (PTFE) - better known as Teflon.
This electrically insulating material is a so-called
electret, which can store electrical charges or
accumulate them through friction, for example. A small
piece of aluminum connects the two layers and serves as
an electrode.
Accumulating charges
If a drop of water now falls on this ensemble, it
spreads out on the water-repellent Teflon surface and
generates an electric charge there through
electrochemical interactions. Unlike previous droplet
generators, this electrical energy is not lost again
after each droplet, but accumulates. "As the number of
water drops hitting the surface increases, the charge on
the surface increases," Wang and his team report. "After
about 16,000 drops, the surface charge reaches a stable
value of about 50 nanocoulombs."
Now a second process comes into play: the water
spreading on the surface forms a bridge between the
aluminum electrode and the ITO and Teflon layers. This
creates an electrical circuit through which the charge
can flow away. As the researchers explain, the way the
system works is similar to that of a field-effect
transistor. According to their data, the drop generator
achieves an energy density of 50 watts per square meter.
One drop lights up 100 LEDs
In initial tests, a prototype of this drop generator
already generated thousands of times more energy than
conventional systems: "A drop of 100 microliters of tap
water falling from a height of 15 centimeters can
generate a voltage of 140 volts and a current of 270
microamperes," Wang and his team report. "This
electrical energy is enough to light up a hundred small
LEDs."
According to the researchers, their drop generator can
be used not only with tap water, but also for seawater
and raindrops. For use in the rain, they adapted the
design so that rainwater is first collected and then
divided by a capillary into small, regularly falling
droplets. Seawater can be dosed in a similar way.
"By adjusting the diameter of the capillary and the
height of the fall, we can control the size and speed of
the droplets, and thus the amount of energy produced,"
Wang and his colleagues explain.
Renewable, decentralized energy
According to the scientists, this technology opens up new
possibilities for harnessing the energy of water. "The
kinetic energy of falling water comes from gravity, so it
can be considered freely available and renewable," Wang
says. "It should therefore be put to better use.
Electricity from water drops instead of petroleum or
nuclear power could advance the world's sustainable
development."
The droplet generator is particularly well-suited for
decentralized power generation, he says. It could be used
to generate electricity wherever rain falls or water is
available - even on the hull of a ferry or on the surface
of an umbrella. (Nature, 2020; doi:
10.1038/s41586-020-1985-6)
