Ocean Oddities: Converting Waves Into Watts

By continuously increasing our consumption of those carbon-based combustibles for the last few centuries, it looks like we may have accidentally warmed the world up a bit too. Realizing that it’s probably best to let nature control Earth’s thermostat, and for us not to monkey with it, people have been pursuing other energy options that can maintain our high standard of living without raising the planet’s temperature.

One of those alternate power sources is something we are all familiar with — the surf. Anyone who has been roughed up by a wave

knows the force of rushing water. People have been utilizing the power packed in moving water since ancient times. For millennium, watermills used flowing rivers to turn their water wheels. The rotating shafts of those massive wooden wheels drove the machinery which ground grain into flour, sawed logs into lumber, and wove thread into cloth.In the last century, watermills were replaced by electric turbines, and water channeled through dams took the place of rivers. That fast and finely controlled flow of water is used to spin blades inside the turbines, which in turn, generates the electricity that energizes our power grid.

So if moving water can be used to make electricity, and waves are energy that are all about moving water once they break, then it seems like the surf should be an endless source of clean energy. Unfortunately, it turns out that harnessing waves for power is much harder than riding them. Way harder.

In September, for the first time ever, electricity created purely by wave power offered just enough juice to light up about a dozen homes, showing that surf could serve as a substantial source of energy.

More than two-third’s of Earth’s surface is covered by ocean water, which is in constant motion. Some of that movement we can see, like when it’s in the form of surf, but most of the sea’s kinetic energy is concealed in currents, gyres and eddies that can circulate on a global scale. If just a small fraction of that worldwide flow were efficiently captured to produce power, we would have electricity that was truly too cheap to meter.

Waves are hard to work with. Since surf is a byproduct of weather, waves can vary in size just as much as winds vary in speed. Due to tidal fluctuations, the spot where swell transforms into surf may continuously move through the course of a day. Large breaking waves can bring instant destruction, while the corrosive saltwater methodically dissolves most metals. Although accessing the unlimited power of the open ocean is mostly a dream at this point, the technology to tap into energy at the sea’s edge exists right now.

In September, for the first time ever, electricity created purely by wave power was fed into the US electrical grid. The energy sent from the sea was produced by a pair of wave-driven generators anchored about a mile offshore from the Marine Corps base at Kaneohe Bay on Oahu, Hawaii, at the Navy’s Wave Energy Test Site. While that inaugural pulse of wave derived power was limited in scale, offering just enough juice to light up about a dozen homes, the electric charge was significant since it successfully demonstrated a method to convert waves into watts and showed that surf could serve as a substantial source of energy.

The Naval test site outside of Kaneohe Bay employs two types of wave converters to create electricity. One is the Azura, a generator that resembles a tall buoy riding vertically in the water and extending 12 feet above the sea surface and 50 feet below the waterline. Consisting of a twin tower hull holding a rotating float, the Azura’s design enables it to extract power from both the vertical lift and horizontal surge provided by passing waves.

The other wave converter is called the Lifesaver due to it’s doughnut-like shape. The 50 foot wide and 3 foot tall buoyant ring is moored in place by cables, with one end of each cable attached to the seafloor and the other end wrapped around the axle of a generator located on the Lifesaver. Riding on the surface, the Lifesaver rises and falls with the waves, which pulls the cables and cranks the generators.

Including the two designs described above, there are six primary types of wave energy converters. Those devices are being used in various coastal areas around the world, including Oregon, California, United Kingdom, Australia and Portugal. But the turbulent nature of the sea can make it an extremely harsh environment for any equipment to operate and endure, so the power produced by all those wave converters combined is barely a spark when compared to the global demand for electricity. Of the major renewable energy sources: solar, hydroelectric, geothermal, wind and waves; the power extracted from surf comes in a distant last place.

If all the challenges inherent in harnessing waves for electricity can be overcome, and its kilowatt cost can compete with the price of power plants that run on fossil fuels, will there come a day when we have to decide which surf spots we’re willing to sacrifice in order to obtain environmentally friendly energy?