Fur-lined double-barrel generator harvests energy from slow waves
Magnets hold the inner cylinder in place, stopping it from rotating until it reaches the peak of a wave, where it can be released to create the maximum triboelectric effect
Researchers at the Pacific Northwest National Laboratory (PNNL) have developed an unusual way to harvest wave power, with a gently rolling cylinder designed around the triboelectric effect that causes static shocks after you walk on certain carpets.
The PNNL team has prototyped a new "frequency-multiplied cylindrical triboelectric nanogenerator," (FMC-TENG) specifically designed to draw power from low-frequency waves out in the open ocean. We're not talking megawatt-scale devices here capable of feeding energy back to the power grid; the team hopes these machines will end up as a practical, lightweight, low-cost way to power open-ocean monitoring platforms that might include several sensors and a satellite communications system.
The triboelectric effect (the prefix tribo- referring to rubbing or friction) is still not fully understood. We all know it exists, because we've all reached for a door handle and got zapped, and there's plenty known about which materials pair up to create the strongest static charges.
The current thinking is that it occurs when two different materials exchange electrons at the molecular level, creating an electrostatic attraction between them. When the two materials are rubbed together, they're effectively separated before those electrons can return home, so a charge is left behind, and the door handle begins to watch you approaching with malevolent glee.
The FMC-TENG uses a cylinder-within-a-cylinder design. The outside of the smaller cylinder and the inside of the larger one are coated with artificial fur, and a Teflon-like material called fluorinated ethylene propylene (FEP) – materials selected for the optimal triboelectric effect when rubbed together. The inner cylinder is free to rotate, and when it moves relative to the outer cylinder, static electricity builds up and is collected by electrodes.
The magnetic braking system takes slow wave oscillations and turns them into faster, more frequent swings between the two cylinders, amplifying the triboelectric power output
Such TENGs have been built and used before, but to make this one effective in slower, more uniform waves such as those in the open ocean, the PNNL team needed to amplify the output, by magnifying the motion between the two cylinders. It did this by magnetically braking the movement of the inner cylinder, stopping it from rotating until it reaches the crest of a wave. At this point, with maximum potential energy, the magnet releases the cylinder and it rolls back much more quickly than it would normally. In this way, a single slow-moving wave can be transformed into a number of quicker rotations between the two cylinders, maximizing the triboelectric effect.
The end result is a more efficient TENG, capable of generating more energy from slower wave movements. “The FMC-TENG is unique because there are very few wave energy converters that are efficient and able to generate significant power from low-frequency ocean waves,” said PNNL laboratory fellow Daniel Deng, co-author of a study published in the journal Nano Energy. “This type of generator could potentially power integrated buoys with sensor arrays to track open ocean water, wind, and climate data entirely using renewable ocean energy.”
The study is available at Nano Energy.
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