Raindrop Energy Capture – Triboelectric Nanogenerator Breaks New Ground

This visual representation details how the D-TENG panels might appear and how their efficiency can be enhanced with the incorporation of the bridge structure and bottom electrodes. Credit: iEnergy, Tsinghua University Press.

The small energy produced when raindrops fall can be collected and transformed into electricity, akin to a microscopic version of hydroelectric power that uses the energy of flowing water. There’s been significant scientific interest in harnessing this power from falling rain as a sustainable, green energy source. However, widespread application of this technology has proven to be a hurdle, restricting its practical use.

A device known as a triboelectric nanogenerator (TENG), utilizing liquid-solid contact electrification, has demonstrated effectiveness in extracting electricity from raindrops. This innovative technology has also been successful in capturing energy from waves and other liquid-solid triboelectric sources.

Despite the high instantaneous power output of droplet-based TENGs (D-TENGs), connecting several panels together presents a technical challenge, thereby limiting the total power production. A recent study has proposed an approach inspired by solar panel arrays to enhance the efficiency of raindrop energy harvesting, broadening its potential use.

The study was published in the iEnergy journal on June 29.

“Although D-TENGs yield a substantial instantaneous power output, it’s challenging for a single D-TENG to sustain power supply to megawatt-level electrical equipment. Hence, it’s crucial to establish a method for the concurrent utilization of multiple D-TENGs,” said Zong Li, a professor at Tsinghua Shenzhen International Graduate School at Tsinghua University, Shenzhen, China. He further proposed an efficient method for raindrop energy harvesting, inspired by the design of solar panels where multiple units work together.

When multiple D-TENGs are linked, an unintended coupling capacitance forms between the top and bottom electrodes of the panels, reducing the power output. To mitigate this issue, researchers suggest the use of bridge array generators that employ array bottom electrodes to diminish the capacitance’s impact.

Triboelectrification, a process where energy from rain is produced and stored when raindrops hit the panel surface, occurs. The raindrop becomes positively charged upon contact with the panel surface, known as the FEP surface, causing the FEP surface to gain negative charges. “Each droplet produces a small amount of charge, and the surface charge on the FEP will slowly dissipate. Over time, the FEP surface charges will accumulate to a saturation point,” explained Li. “At this point, the dissipation rate of the FEP’s surface charge balances the charge generated by each droplet’s impact.”

The effectiveness of the bridge array generators, with array bottom electrodes, was demonstrated by comparing them to conventional D-TENGs. Researchers also examined the performance of bridge array generators with varying sub-electrode sizes. The thickness of the panels was studied to understand its impact on power loss. Increasing the FEP surface thickness reduced coupling capacitance and preserved surface charge density, which could enhance the bridge array generator’s performance.

When bridge array generators, with array bottom electrodes and bridge reflux structures, were designed for raindrop energy collection, the panels could operate independently, minimizing power loss. “The peak power output of the bridge array generators is almost 5 times higher than traditional large-area raindrop energy collectors of equivalent size, achieving 200 watts per square meter. This clearly highlights its superiority in large-scale raindrop energy harvesting. These findings provide a viable solution for large-scale raindrop energy harvesting,” stated Li.

Reference: “Rational TENG arrays as a panel for harvesting large-scale raindrop energy” by Zong Li, Bin Cao, Zhonghao Zhang, Liming Wang and Zhong Lin Wang, 29 June 2023, iEnergy.
DOI: 10.23919/IEN.2023.0015

Other team members involved in the study include Bin Cao and Liming Wang from the Tsinghua Shenzhen International Graduate School at Tsinghua University; Zhonghao Zhang from the China Electric Power Research Institute, Beijing; and Zhong Lin Wang from the Beijing Institute of Nanoenergy and Nanosystems at the Chinese Academy of Sciences, Beijing.

This research was funded by the National Natural Science Foundation of China (52007095).

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