Raindrops contain abundant renewable energy, including both kinetic energy and electrostatic energy, and how to effectively harvest it is becoming a hot research topic.
1. Clean energy from raindrops
Researchers at Tsinghua University in Shenzhen, China, have proposed that the energy collected from raindrops could be a potential source of clean, renewable power. However, this technology has been difficult to develop on a large scale, which has limited its practical application. The scientists are driven by the technology behind solar panels and have already published their scientific progresses in iEnergy.
When raindrops fall from the sky, they can produce a small amount of energy that can be harvested and turned into electricity, the paper explains, noting that it is a small-scale version of hydropower, which uses the kinetic energy of moving water to produce electricity.
2. Harvesting
But how is the energy harvested from raindrops? To collect raindrop energy, a device called a triboelectric nanogenerator (TENG), which uses liquid-solid contact electrification, has been shown to successfully harvest the electricity from raindrops, the team said.
Based on previous research work, droplet-based TENG (D-TENGs) have displayed technical limitations from connecting more than one of these panels together, which reduces overall power output. But the new published scientific paper outlines how modeling D-TENG panels after solar panel arrays makes harvesting raindrop energy more efficient, broadening its application.
“To this end, a “solar panel-like” bridge array generators (BAGs) is proposed. BAGs adopt array lower electrode (ALE) and bridge reflux structure (BRS) to make each power generation unit independent of each other, as well as eliminating the influence of electrodes that preserve the peak power output of large-scale D-TENGs,” reads the paper.
3. Inspired by solar panels
Essentially, the team of researchers led by Zong Li, a professor at the Tsinghua Shenzhen International Graduate School in China, took inspiration from solar panels to set up bridge array generators and reduce the influence of capacitance.
“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,” said Zong Li, professor at the Tsinghua Shenzhen International Graduate School at Tsinghua University in Shenzhen, China. “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.”
When raindrops fall on a surface of a panel of the D-TENG, called the FEP surface, the droplet becomes positively charged while the surface becomes negatively charged, explained a press statement about the peer-reviewed study.
“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,” reads the press release. “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.”
4. Measuring success
In order to demonstrate the success of the bridge array generators with the array lower electrodes, the conventional D-TENG was compared to the bridge array generators. Researchers also compared the performance of the bridge array generators with different sizes of sub-electrodes. The thickness of the panels was also studied to see if that had an effect on any power loss. They found that increasing the FEP surface thickness leads to decreased coupling capacitance while maintaining the surface charge density — both of which could improve the performance of the bridge array generator.
The discovery could revolutionize new ways of harnessing renewable energies, and bring about clean solutions in areas that see incessant rain for a large number of days in the year.
