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Rain: The Next Renewable Energy Source

Alternative Energy

The need for new sources of renewable energy has scientists looking in some unexpected places. From the motion of the waves, to human activity, potential energy solutions are popping up all over. Now, experts are excited about a new possible source of clean, renewable power: rain.

How could rain provide electricity?

Some materials are able to generate a small charge using the triboelectric effect. This occurs when two different substances come in contact with each other, and then are separated—think of it as akin to static electricity. A balloon (which is negatively charged) rubbed against a cat (positively charged) can create a charge, as can a piece of amber rubbed against wool. The trouble with the triboelectric effect is that it is unreliable. A lot of outside factors, like surface texture, temperature, and humidity, can affect the amount of electricity that results. This makes is an unreliable means of generating power.

Rain can also produce electricity through the piezoelectric effect. This happens when one object puts pressure on another object made of a piezoelectric material. So, the pressure of falling raindrops could be enough to produce a small amount of electricity. Unfortunately, this amount is too insignificant to be a reliable source of power.

Lastly, the motion of rain could be enough. Waterwheels and hydroelectric dams already rely on the motion of water to generate electricity, so there's really nothing stopping anyone from applying a similar principle to rain. Above-ground reservoirs could catch large amounts of it, dispensing it into water-powered turbines that produce electricity.

What's currently in the works?

Researchers in the U.S. and Hong Kong have created a Droplet Electricity Generator capable of producing roughly 140 volts from a single raindrop—enough to power 100 LED bulbs for a short amount of time. The generator pairs an aluminum electrode with an indium tin oxide electrode under a layer of tetrafluoroethylene (PTFE). PTFE is a polymer with a quasi-permanent negative electric charge. When a drop of water hits the PTFE layer, it closes the circuit between the two electrodes and releases the stored charge. The droplets effectively act like resistors, while the PTFE coating is a capacitor.

Students at the Technological University of Mexico have another possible method. They developed a microturbine that uses rainwater to generate electricity, which then compensates for the power required to purify drinking water. This allows for a sustainable method of producing clean, potable water.

Researchers at the Ocean University of China and Yunnan Normal University have also developed an all-weather solar panel. This device is designed to harvest sunlight like conventional photovoltaic cells, then be able to switch to generating power from rainwater. When a drop of rain hits the cell, it is broken up into positive and negative ions. The positive ions, largely salts, collect on an aqueous graphene surface and create layers that act as pseudocapacitors. The difference in potential between these layers produces electricity.

Scientists from CEA/Leti-Minatec developed another system, generating energy from the vibration of a raindrop landing on a piezoelectric structure. It relies on a 25 micrometer-thick layer of polyvinylidene fluoride (PVDF). When this layer is hit by a raindrop, it vibrates. Electrodes set into the PVDF collect the energy generated by these vibrations.

Who's developing the technology?

Rain power is still squarely in the proof-of-concept stages. While scientists have made some surprising breakthroughs, there's still a long way to go before rain can be considered a viable source of clean, reliable power. This means that the research is primarily taking place in universities, rather than private companies.

When will rain power be a reality?

Rain power is still years away. With so many potential avenues for research and development, there's a lot to consider before finding the best option. Right now, researchers are hoping that the Droplet Electricity Generator might be able to be embedded into things like water bottles, umbrellas, and roofing material—anything that comes in contact with water on a regular basis. These designs are still very theoretical, and it'll be awhile before they are viable. While promising, this technology's conversion efficiency is still too low to implement just yet.

What are the potential roadblocks to rain power?

The biggest challenge faced by rain power is inefficiency. While it's great news that a single raindrop was able to light 100 LED lights, that doesn't really translate to powering homes or businesses. Now that researchers know ways to gather electricity from raindrops, the next step becomes how to generate it efficiently enough to position it as a competitor to nuclear or coal power.

Solar and wind power are the frontrunners when it comes to renewable energy, but they have their drawbacks. Generating electricity from rain would allow us to produce power regardless of a lack of sunlight or wind, creating a more comprehensive, viable green energy system. While the developments in this field are still in their infancy, the technology is already showing a lot of promise.