Researchers are homing in on a viable alternative or supplement to solar photovoltaic panels: rain panels. These power-generating rain panels can harvest, store and use electricity generated from the energy of falling rain.
Although wave power collection systems and hydroelectric dams use the kinetic energy from the movement of water to generate electricity, earlier versions of rain panels faced seemingly insurmountable technical obstacles that limits their use on a large scale. One of the challenges has been overcoming “coupling capacitance,” which occurs between the upper and lower electrodes of each cell in the panel, because too much power is lost from cell to cell, even when a series of cells is combined.
The panels incorporate a triboelectric nanogenerator (TENG) that uses a liquid-solid contact electrification to collect the small but measurable amount of energy produced by each raindrop hitting the panel. Droplet-based TENGs (D-TENGs) are limited from connecting more than one of the panels, so power output is reduced.
The D-TENGs have high instantaneous output power, but because it would be difficult for one to individually power megawatt-level electrical equipment, it’s necessary to use multiple units.
Zong Li, professor at Tshinghua Shenzhen International Graduate School and one of the authors of the proposed method, and his team is looking at using “bridge array generators” to overcome the issue of coupling capacitance. Combining the D-TENGs in a configuration to reduce the coupling capacitance issue could make the difference.
The generators keep cells operating separately by using lower array electrodes. This process is a new way of arranging cells in a series array to collect and store energy. Raindrops fall onto the panel surface (called the FEP surface) and become positively charged, while the FEP surface becomes negatively charged.
“The amount of charge generated by each droplet is small and the surface charge on the FEP will gradually dissipate,” Li explained. As the charge dissipates, energy will be lost.
The bridge array is designed to overcome that loss. “After a long time on the surface, the charges on the FEP surface will gradually accumulate to saturation,” Li said. “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.”
Research indicates that increasing the thickness of the FEP surface leads to decreased coupling capacitance while maintaining the surface charge density, both of which could improve the performance of the bridge array generator.
In addition to identifying the correct surface thickness, researchers said making the individual cells work independently can reduce the coupling capacitance enough to make energy collection from rain panels an efficient option.
Developing bridge array generators for collecting raindrop energy and using lower array electrodes and bridge reflux structures makes the panels independent of one another, which reduces power loss.
“The peak power output of the bridge array generators is nearly five times higher than that of the conventional large-area raindrop energy with the same size,” Li observed. It reaches 200W per square meter—an advantage in large-area raindrop energy harvesting.
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