Floating Nanogenerators Turn Wave Motion Into Sustainable Energy

At this point, we're all well aware of the growing need for renewable energy sources with solar panels and wind turbines increasingly being used to supply "green" power. Now researchers have found a new way to tap the motion of the ocean to produce renewable "blue" wave power.

Ocean waves could offer a valuable new renewable power supply.Ocean waves could offer a valuable new renewable power supply.

The need for renewable energy is by no means a new story. Between our diminishing reserves of fossil fuels, steadily rising population, and the increasing concentration of carbon dioxide in our atmosphere, it is now very clear that new solutions are needed to meet worldwide energy demand. Currently, solar and wind energy technologies are on the front lines of this challenge; however, deriving useable energy from our oceans -- which occupy 70% of the planet's surface -- is a potentially transformative alternative. Producing power from water waves offers several unique advantages in that it is relatively independent of season, time of day, weather, and temperature.

The usual method by which wave energy is extracted is to rely on the electromagnetic effect, but this has some unfortunate drawbacks. The requisite magnets and metallic coils are heavy and require the addition of bulky floatation devices in order to function. This bulk limits the density with which the generators can be implemented and increases material costs. Additionally, high-end materials are often needed for efficient energy conversion which further renders these systems to expensive for practical use.

Now scientists report a new method of extracting power from waves relying instead on the triboelectric effect. The triboelectric effect is what you experience when you rub glass with fur or run a comb through your hair; certain pairs of materials, when brought into contact, become electrically charged. The researchers took advantage of this effect by using wave motion to bring a pair of such materials into and out of contact leading to a continuous flow of electric charges. 

Triboelectric nanogenerator: Reprinted with permission from ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b00534. Copyright 2015 American Chemical Society.Triboelectric nanogenerator: Reprinted with permission from ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b00534. Copyright 2015 American Chemical Society.

The device consists of two arched top and bottom plates made of light-weight, inexpensive, and (important in seawater) resistant to corrosion plastic. Inside are nanowires of the polymer PTFE, better known as Teflon, separated by a small distance from an aluminum plate. When subjected to the motion of waves, the arched exterior is compressed and released leading to intermittent contact between the aluminum and the nanowires and the production of harvestable triboelectric energy.

While each of these nanogenerators yields minimal power individually, their true value stems from the way they can be integrated into large-scale floating networks. An average power output of 1.15 MW is predicted from just one square kilometer of ocean surface coverage, enough to power 500 - 1000 homes for a year and to justify ingoing research efforts in this area.