Generator Redesign Tries to Catch a Good Wave

While many ocean energy projects think big, laying large buoys that convert waves into electricity through mechanical means, there is another approach to developing wave energy: going small. For more than a decade, materials scientists have been tweaking materials on tiny scales to harvest electric charge from moving water. Now, by making a fundamental change to one such device’s design, a group at Central South University in Changsha, China, has managed to more than double its current collection capabilities.

To be precise, the Changsha group’s device is called the triboelectric nanogenerator (TENG). True to their name, TENGs rely on the triboelectric effect: If one material rubs across another, electric charge can transfer from one to the other. Given the correct materials, a TENG can then harvest that moving charge as electricity. The “nano” part comes in the material: Creating an effective TENG requires shaping the material with very small structures in order to tweak the electric exchange into drawing more current.

New ideas in wave energy are needed. The field has had plenty of false starts, and less than a gigawatt of capacity has been installed so far. But one optimistic scenario posits that the world might host 100 gigawatts of wave power by 2050. Wave power is particularly attractive for island nations and remote island communities, where land for power plants can be scarce, but waves are plentiful.

Nanogenerators Go Triboelectric

The TENG is a relatively recent invention. Materials scientists from the University of Science and Technology Beijing and Georgia Tech first created one in 2012 while attempting to construct a magnetic-field sensor. Researchers quickly realized that the device could work as an energy harvester. A year later, the same Georgia Tech group unveiled a TENG that relied on water. As waves of water washed across an array of nanoscale silicone pyramids, the apparatus generated a very small current.

Part of why researchers are so keen on these kinds of liquid-solid combination TENGs is that the water itself is one of the partners in the electric exchange. The device therefore should suffer much less wear and tear from friction. What’s more, it doesn’t need springs, rotors, turbines, or any other mechanical components. However, liquid-solid TENGs have a long way to go before they can find use as a reliable power source. They don’t produce enough current to be useful, and they don’t generate current with the reliability that is required.

The Changsha group’s device generated 3.5 times the voltage and 2.3 times the current of earlier designs.

So even the gadget’s basic design is still under scrutiny in an effort to improve its performance. A standard liquid-solid TENG might look like a sealed tube, partly filled with water, and with an electrode placed in its middle. As the tube rocks back and forth in the waves, water sloshes around inside and crosses the electrode to generate current.

The Changsha…