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| Fig. 1: Picture of a wave energy prototype testing. (Source: Wikipedia Commons) |
Over seventy percent of Earth's surface is covered by water, and with scientists desperately searching for alternative energy sources, the big question becomes "How can we use water for energy?" Simply put, the answer is: waves. Waves are created by wind blowing across the surface of the oceans, and in multiple areas around the globe the wind blows with enough force and consistency to produce impressive and continual waves along the shorelines. As a result, ocean waves contain tremendous energy potential. Various groups around the globe have begun developing projects geared toward building wave power devices with the goal of extracting energy from the surface motion of the waves and pressure fluctuations happening below the water's surface.
Given the oceans tremendous power, wave energy has arrived as a very promising alternative energy source. According to the Wilson and Beyene, if only 0.2% of the of the energy in the world's ocean waves were harnessed, it would supply all of the current world's energy demand as a renewable resource. [1] Studying the West Coast, California specifically, the deep continental shelf creates a tremendous amount of energetic waves and water power relatively close to the shore. This potentially promises a great energy source for a large population. In contrast, the East Coast though having similar waves in height and power has a wide continental shelf that induces large bottom- friction loss to the waves making it nearly impossible to harness their energy. [1]
As of right now a wide range of energy devices have been prototyped, to deal with either scenarios of continental shelfing. However, only a small fraction have actually gone through testing and serious evaluation. Tremendous disparity exists among the various technologies used due to the innumerable problems harnessing waves produces. While one system may remain in a fixed position and let waves pass overtop, another may follow the patterns of the waves and move with them depending on the power, strength and orientation of the waves and tides. [1] Four basic devices exist, an example of one appearing in the image on the right: A protype testing of a Attenuator device.
Terminator Devices: onshore or nearshore, extends in a perpendicular direction in comparison to the waves and captures the water through a subsurface chamber reflecting the power of the wave. [2]
Attenuators: ride the waves like a boat and consist of long multisegment structures parallel to the direction of the waves. [2] Extracts energy by using hydraulic pumps and natural variations of wave height. [2]
Point Absorber: floats on the water, and moves its components relative to the movement of the waves. [2] Similar to a giant buoys, it uses the rise and fall of wave height at single points to create energy. [2]
Overtopping devices: Placed on the surface of the water, they mimic giant reservoirs; allowing incoming waves to fill them up and cause water pressure to buildup. [2] Like a dam, the water is released and the energy created by this action drives hydro turbines to generate power. [2]
In short, wave energy is concentrated at low frequencies and at low alternating velocties, which makes efficient conversion and transmission to a grid difficult and limits the options for efficient power takepff technology. [2] So while an abundance of wave energy is available, it cannot be harnessed everywhere and runs a very large monetary cost. [3] Although numerous studies have confirmed the fantastic contribution tidal and wave power has towards the big picture of energy, the industry has come to a slowing halt due to the large expenses needed for research and building projectable ideas. Over the last two decades, companies have worked to develop potential designs capable of harnessing the waves, but one of the biggest problems, as mentioned above, lies in the design process. From a technical point of view operating devices in the ocean is far more taxing than on land. [3]
With drastically divergent concepts currently being tested, there is not one definitive design that has proved more successful than the rest. With the ocean providing little favors, it proves to be a hostile environment with the waves themselves contributing challenges. The equipment and devices are easily damaged by the incessant beating of the waves and forceful power of the water, especially during storms. This damage requires money, money generated in capital-intensive investment funding, funding that just doesn't exist nor is a priority.
Wave power energy converters located at deep ocean sites have proven to generate three to eight times the wave power in comparison to onshore or costal sites. [2]
As of recently one pilot project has emerged above the rest backed with substantial funding by Carnegie Wave Energy, a company based in Perth, Australia that has over $100 million invested in technology and project development. [3] Carnegie has built three big buoys floating beneath the coast of Western Australia; thirty-six foot steel machines, consistently battered by the waves of the Indian Ocean. [3] Currently, the buoys generate around five percent of the electricity used at a nearby military base by harnessing the constant motion of the waves. [3] A pilot project, named "Ceto 5" has worked to battle the design difficulties associated with wave energy. The buoys rest three to six-feet underwater, protecting them from the continuous pounding of the waves. [3] This constant rocking is what drives the hydraulic pumps located inside the buoys, that push seawater through a pipe and eventually a power plant located two-miles away. There, the high pressure water turns standard electric turbines powering a generator. [3]
What makes this design quite unique is the process of pumping the high pressure water. The buoys push the water through the desalination plant, without using fossil fuels. Right now, Carnegie is already planning to build larger, better-designed buoys starting in 2017. [3] These improved models, increasing to sixty-five feet wide will potentially generate one megawatt of electricity each (four times the energy of the current prototype). [3] The new technology would produce electricity inside the buoy instead of at an onshore power plant. [3]
© Kelly Myers. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Wilson and A. Beyene, "California Wave Energy Resource Evaluation," J. Coastal Res. 23, 679 (2007).
[2] J. Scruggs and P. Jacobs, "Harvesting Ocean Wave Energy," Science 323, 1176 (2009).
[3] A. Yee, "Catching Waves and Turning them Into Electricity ," New York Times, 22 Apr 15.
