Recently, the shortage of fossil fuels and the increasing electricity demand have sparked enthusiasm for exploring renewable energy. As an important part of the natural energy and water cycle, rainfall contains abundant renewable energy.
When raindrops fall from the sky, they can produce a small amount of energy that can be harvested and turned into electricity. It is a small-scale version of hydropower, which uses the kinetic energy of flowing water as it moves downstream to produce electricity. However, this technology has been difficult to develop on a large scale, which has limited its practical application.
Recently, a triboelectric nanogenerator (TENG) using liquid-solid contact electrification has been shown to successfully harvest raindrop energy and ocean energy. Currently, we have excellent droplet-based TENG (D-TENGs) to harvest energy from a single water droplet. But it is still difficult for a single D-TENG to continuously supply power for megawatt-level electrical equipment.
Now, researchers at Tsinghua University in Shenzhen, China, have modeled D-TENG panels after solar panel arrays to make harvesting raindrop energy more efficient, broadening its application. Researchers took inspiration from the design of solar panels in which multiple solar power generation units are connected in parallel to supply the load.
When multiple D-TENGs are connected, there is an unintended coupling capacitance between the upper electrode and the lower electrode, which significantly reduces the peak power output of the D-TENG arrays.
To overcome this problem, researchers proposed bridge array generators, which use array lower electrodes to reduce the influence of the capacitance. When the droplet falls on the surface of the panel, called the FEP surface, the droplet becomes positively charged, and the FEP surface negatively charged.
“The amount of charge generated by each droplet is small, and the surface charge on the FEP will gradually dissipate. After a long time on the surface, the charges on the FEP surface will gradually accumulate to saturation,” said Zong Li, a professor at the Tsinghua Shenzhen International Graduate School at Tsinghua University in Shenzhen, China. “At this point, the dissipation rate of the FEP’s surface charge is balanced with the amount of charge generated by each impact of the droplet.”
Researchers used bridge array generators with different sizes of sub-electrodes and various thickness panels to see if that had an effect on any power loss.
Bridge array generators utilize array lower electrodes and bridge reflux structures to make power generation units independent of each other, as well as eliminate the influence of electrodes which remain the output power of large-scale D-TENGs high and independent from the size.
“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,” said Li.