Electrical Energy from Stretching Yarn

by Emil Morhardt

Well, yarn, sort of. This yarn is made by twisting carbon nanotubes until they become so twisted that the coil up into a helical spring-like configuration. You can do the same thing with cotton yarn or string. When the South Korean researchers (Kim et al., 2017) put the coil into an electrolyte then stretched it what they got was electrical current. Not a lot, but these are small laboratory-scale experiments and what the researchers had in mind was generating small amounts of energy to power sensors, for example, sewn into a shirt or gloves that are stretched and released under normal activities, but that wouldn’t work very well if the subject had to be immersed in an electrolyte. Or would it? They tried immersing the device, which they call a twistron, into the Gyeonpo Sea off South Korea where the temperature was 13ºC (a chilly 55ºF) and the sodium chloride content was 0.31 M, a nice electrolyte solution. But instead of sewing the yarn into a diver’s wetsuit, they attached it between a floating balloon and a sinker on the seabed to see if they could harvest ocean wave energy. Yes! They got it to light up a green LED whenever a wave came by. Continue reading

Undersea Ocean Renewable Energy Storage

Ocean Energy Storage

by Allison Kerley

Slocum et al. (2013) propose a new design for an energy storage and generation unit composed of underwater concrete spheres and offshore wind turbines. The proposed design utilizes pumped storage hydraulics (PSH). During times of low energy demand from the grid, the cylinder would contain water at equal pressure with the surrounding ocean. In the proposed design, the floating wind turbines generate energy and the excess energy is used to pump water out of the storage sphere, creating a vacuum. When energy is needed from the sphere, the turbine would open, allowing water to pass through into the sphere. The proposed sphere design would have an inside diameter of 25 m, and would retain a 1/20th-atm environment when fully discharged. The proposed design could be used without alteration in depths between 200 and 700 m, and would continue to be economically feasible to a depth of approximately 1500 m. The authors tested a small-scale dry version of the proposed design, with the test sphere having an inner chamber diameter of 75 cm, with a ten meter height difference from the top of the pump and wind turbine to the top of the sphere. The test unit was found to have a low round-trip efficiency of 11%, which the authors attribute to their inability to use the most efficient pump and turbine technology due to the small size of their test model. They calculated that in a full scale model, the lowest round-trip efficiency would be 70%. Continue reading