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Water power: water drip generator producing current 01

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presented by Michael Palomino

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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/
Structure of the drop generator in the scheme
                    and photo. © City University of Hong Kong/ Nature
Structure of the drop generator in the scheme and photo. © City University of Hong Kong/ Nature

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)

Source: City University of Hong Kong>






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