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Tuesday, 11 February 2020

New Electricity generator powers 100 small LED bulbs with a single drop of water

City University HK

Liquid water is omnipresent on Earth, from rivers to oceans through rain. However, the energy potential it contains is still insufficiently exploited. Recently, a team of Chinese engineers has developed a new method capable of harnessing the kinetic energy of water movements, such as falling raindrops, and converting it into electricity. A single drop of rain could thus power 100 LED bulbs.

A single drop of rain can now power 100 small LED bulbs, setting a new milestone for energy generation technologies. The droplet-based electricity generator developed has a high energy conversion efficiency and a power density a thousand times greater than its counterparts. The study was published in the journal Nature .

The developers hope the technology will help tackle the global energy crisis by providing new ways to use the environmental energy that surrounds us in water and rain. The generator could be used in a variety of contexts where water meets a solid surface - such as on boat hulls, along coasts and even above shelters or umbrellas.

“Our research shows that a drop of 100 microliters of water released from a height of 15 centimeters can generate a voltage of more than 140 volts. The power generated can light up 100 small LED bulbs,” said Zuankai Wang, engineer at City University of Hong Kong.

Limited current hydroelectric technologies

Although the concept of hydroelectricity is not new - hydroelectric dams and tidal power plants operate around the world, the limitations of current technology have prevented us from taking full advantage of the available energy from waves and raindrops. This power is in the form of low frequency kinetic energy. “The kinetic energy caused by waterfalls is due to gravity and can be considered free and renewable. It should be used better.”

Conventional droplet energy generators take advantage of the triboelectric effect, in which electricity is generated when certain materials come into contact with each other, friction causing them to exchange electrons . Unfortunately, the size of the charge that can be generated on such surfaces is generally very limited, leading to very low energy conversion efficiency. The researchers' new energy recovery method overcomes these limitations in two different ways.

Optimized electricity generation thanks to polytetrafluoroethylene

First, the team used a material called polytetrafluoroethylene (or PTFE), which has an almost permanent electrical charge. They found that when drops hit the PTFE, the charges on its surface gradually accumulated until reaching a saturation point - which allowed them to overcome the bottleneck presented by the previous approaches, which could not accumulate only small charges.

(Left): the technology uses the kinetic energy generated by the drop of the drops on the electrodes in order to generate electricity. (Right): diagram of the structure of the PTFE-based device. Credits: City University HK

The second characteristic of the new method is its resemblance to a field effect transistor - a basic element of modern electronics and for which the 1956 Nobel Prize in physics was awarded. The design of the power generator includes two electrodes - one made of aluminum, the other made of tin and indium oxide with a PTFE coating, on which the charge is generated.

Many potential applications

When droplets fall on this last surface, they connect the two electrodes, transforming the original configuration into an electric circuit in a closed loop, releasing the stored charge and generating an electric current to power the LEDs. The researchers also found that the technique is not affected by lower relative humidities - and that it works with both rainwater and seawater.

According to the researchers, the concept could be used on various surfaces where liquids come into contact with solids, to fully exploit the low frequency kinetic energy that can be found in water. Professor Wang said he hopes the technology will help harvest energy from water to tackle the global problem of renewable energy shortages. Researchers have patented their technology in the United States and mainland China.


Article: A droplet-based electricity generator with high instantaneous power density.

Authors: Wanghuai Xu, Huanxi Zheng, Yuan Liu, Xiaofeng Zhou, Chao Zhang, Yuxin Song, Xu Deng, Michael Leung, Zhengbao Yang, Ronald X. Xu, Zhong Lin Wang, Xiao Cheng Zeng & Zuankai Wang

Nature (2020).

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