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February
17
2020

The Next Renewable Energy Source Could Be Rain
Irina Slav

The quest for the next source of renewable energy is well under way, with no natural phenomenon overlooked. We have already harnessed the power of flowing water, wind, and sunlight, and the search for the next clean source of energy is far from over.

The latest potential breakthrough in renewable energy comes in the form of rain.

Rain has not been getting a lot of attention in renewable energy circles perhaps because it would be challenging to harness its electricity-producing potential. Yet attempts are being made, and in the latest breakthrough, U.S. and Hong Kong researchers have managed toproduce 140 volts of power from one single raindrop. That’s enough to light 100 LED lights for a short while.

The idea itself is not new. Previous attempts to generate electricity from rain drops have been made and they have all utilized the triboelectric effect: this is when certain materials acquire an electric charge after they come in contact with another material and then get separated. Think of it as a type of static, low-charge electricity. Yet all of the previous attempts have suffered the limitations of technology.

The team behind the new raindrop power generator has pushed these limits further. The researchers, from City University in Hong Kong and the University of Nebraska-Lincoln, spent two years working on the energy density of what they have called a droplet electricity generator, or DEG.

What they did was use the design of field-effect transistors – three-terminal devices that use an electric field to control the flow of electric current through them. Thanks to this design, the energy density of the DEG shot up to over 50 Watts per square meter, which is thousands of times more than the energy density of comparable devices.

But that wasn’t all. In their quest for a way to harness the power of rain drops, the scientists also used a special material to coat the generator. Called tetrafluoroethylene, or PTFE for short, this is a hydrophobic polymer that doesn’t get wet and can withstand high temperatures. It also has what the scientists call a quasi-permanent electric charge. When a ran drop hits the PTFE surface of the generator, it bridges the two electrodes creating a closed-loop circuit that releases any stored energy charges in the surface material, Engadget explains.

It’s still a long way to go before we all start using PTFE-coated umbrellas with electrodes underneath. But in the future, we may live in buildings with rooftops that double as power generators using the kinetic energy of the water clouds’ release.

Other attempts to use the power of raindrops involve kinetic energy, or the energy of the drops falling from the sky. These attempts have utilized the piezoelectric effect. When an object falls on another object, it applies pressure on it. This pressure, very basically, creates an electric current if the second object is made from a piezoelectric material. So, raindrops falling on a piezoelectric material surface will generate electricity. Unfortunately, what is in science called a conversion rate or conversion efficiency, is extremely low in these designs and, bluntly put, not really worth the effort.

But how about turbines driven by collected raindrops using the same principle as hydropower plants? This is another viable way of utilizing rain. All it takes is building a large reservoir to collect the rainwater above the ground and then use the water to power a turbine. This method could be particularly suited for parts of the world with a monsoon, which would generate ample supplies of rainwater for this alternative hydropower system.

And then there is the microturbine developed by students from the Technological University of Mexico, that uses rainwater to generate electricity. The principle is the same as any that is used in a hydropower plant—the difference being this electricity compensates for power used to purify rainwater. It is a two-in-one solution aimed at providing clean drinking water to poor parts of Mexico City and recovering some of the electricity used in the process by generating it with the remaining unpurified rainwater. 

There is even a solar cell that can harness the kinetic energy of rain, which makes for a nice solution of the problem that rain causes for solar panels: they can’t generate electricity in overcast conditions. Yet if you cover the panel with a layer of grapheme, the miracle material turns into a capacitor, and the difference between its electrons and the ions of the raindrops generates electricity on contact.

The world of renewable energy is becoming increasingly fascinating. Everything is fair game in the search for the next infinite, emission-free source of electric energy. With rain, the basic technology is already there. Now, the challenge seems to be to boost the conversion efficiency of this technology to make rainwater a viable alternative to emission-producing power generation systems.

By Irina Slav for Oilprice.com

 

 

 

Irina is a writer for the U.S.-based Divergente LLC consulting firm with over a decade of experience writing on the oil and gas industry.

 

 

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