Electricity from the Sky: Harnessing raindrop energy

Electricity from the Sky: Harnessing raindrop energy
by Simon Mansfield
Sydney, Australia (SPX) Jul 25, 2023

At Tsinghua University in Shenzhen, China, scientists are refining a novel method to generate electricity from an overlooked and ubiquitous source - raindrops. Mirroring the underlying principles of hydropower but on a micro-scale, the energy inherent in falling raindrops can be converted into electricity, offering a promising avenue for renewable, clean energy generation.

The technology capitalizes on a device known as a droplet-based triboelectric nanogenerator (D-TENG), which employs liquid-solid contact electrification to generate electricity from the kinetic energy of raindrops. This form of triboelectric power generation isn't only limited to raindrops, it's also been successfully utilized to generate power from ocean waves and other liquid-solid interfaces.

However, upscaling the technology to more practical applications has been met with significant hurdles. The main challenge was found in connecting multiple D-TENG panels together, which was discovered to reduce the overall power output due to an issue called unintended coupling capacitance between the panels' electrodes. A recent publication highlights how designing these D-TENG panels similar to solar panel arrays could make the process more efficient and allow for larger-scale energy generation.

Tsinghua University professor Zong Li explains the necessity of such innovative approach: "Although D-TENGs have ultra-high instantaneous output power, it is still difficult for a single D-TENG to continuously supply power for megawatt-level electrical equipment. Therefore, it is very important to realize the simultaneous utilization of multiple D-TENGs. Referring to the design of solar panels in which multiple solar power generation units are connected in parallel to supply the load, we are proposing a simple and effective method for raindrop energy harvesting."

The study details the usage of bridge array generators, specifically devised to reduce the influence of the unintended coupling capacitance. As raindrops fall onto the panel's surface, a process called triboelectrification comes into play, generating and storing energy. Each falling droplet creates a charge - positive for the droplet, and negative for the panel's surface, known as the FEP surface. Over time, the accumulated charges reach a saturation point where the rate of dissipation balances with the newly generated charge.

To validate their innovation, the team compared traditional D-TENG devices with the new bridge array generators, also taking into account variations in the sub-electrodes' sizes and panel thickness. These comparisons revealed that an increase in the FEP surface thickness led to decreased coupling capacitance while maintaining surface charge density, contributing to an improved performance of the bridge array generator.

The team developed bridge array generators with array lower electrodes and bridge reflux structures specifically for raindrop energy collection. This structure allowed the raindrop collection panels to operate independently, effectively mitigating unintended power loss. According to Li, "The peak power output of the bridge array generators is nearly 5 times higher than that of the conventional large-area raindrop energy with the same size, reaching 200 watts per square meter, which fully shows its advantages in large-area raindrop energy harvesting. The results of this study will provide a feasible scheme for large-area raindrop energy harvesting."

The research was a collaborative effort involving scientists from Tsinghua University, the China Electric Power Research Institute in Beijing, and the Beijing Institute of Nanoenergy and Nanosystems at the Chinese Academy of Sciences.

Research Report:Rational TENG arrays as a panel for harvesting large-scale raindrop energy