Scientists Find Way To Convert Water Droplets Into Energy

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By Tsvetana Paraskova

Scientists have been trying for years to harvest energy from the movement and impact of water droplets and other sources of mechanical energy. Researchers from the University of Twente and South China Normal University said this week that they had managed to design and test a generator of electricity using the movement of water droplets and other mechanical energy.

The new approach to generating electricity is not limited to the mechanical power of droplets only, the researchers say.

“Our method can also be considered for other applications where mechanical energy needs to be converted into electrical energy, for example in wearables, from tidal waves, or for sensing,” says Niels Mendel, one of the authors of the new research published in the Advanced Materials magazine.

The researchers propose the so-called charge trapping?based electricity generator (CTEG) to passively harvest energy from water droplets with high efficiency.

“By utilizing CTEG, we could overcome important bottlenecks of conventional nanogenerators, namely the low power density, the low and unstable surface charges density along with poor long?term reliability,” the authors of the paper wrote.

The scientists’ novel approach consists of injecting charges into an insulating layer of the electricity generator by using an innovative charging method based on electrowetting. This is the process of modifying the ability of liquids to stay in contact with a solid surface in the electric field. The impact of the droplet generates an electrical current.

After testing their approach, the researchers succeeded in converting nearly 12 percent – 11.8 percent – of the mechanical energy of the droplet into electrical energy. According to the scientists, this is a significant improvement in efficiency in generating electrical energy from similarly constructed devices.

The researchers also demonstrated that the energy-harvesting efficiency does not degrade after 100 days, requiring only a single 15-minute charging cycle before long-term application.

The new method of generating electrical energy from mechanical energy is not limited to the droplet-based technology, as the team says, so its potential applications could go beyond using rain, for example, to produce electricity, perhaps at some point in the future.

This novel approach is the latest attempt from scientists to use all available abundant clean resources to generate energy, considering the global drive away from fossil fuels and onto renewable energy sources in order to curb the worst effects of climate change.

Research into droplet-based technology for generating electrical energy advanced earlier this year, when a team of U.S. and Hong Kong researchers managed to produce 140 volts of power from one single raindrop. That’s enough to light 100 LED lights for a short while. The team from City University in Hong Kong and the University of Nebraska-Lincoln had 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.

Making rain or other sources of mechanical energy really work on a scale will need a lot of additional research and years to test and analyze to see if this could be a commercially viable source of low-cost, abundant renewable energy. The global push from investors and governments for a more prominent role of zero-carbon energy sources could further incentivize researchers with grants to look into developing simple enough devices that could harvest energy from sources of mechanical energy, including raindrops.

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