Harnessing the enormous power of ocean waves has recently gained popularity as a form of renewable energy that does not contribute to global warming. Seventy percent of the world’s electricity needs are met by burning fossil fuels such as coal or natural gas, and these methods generate vast amounts of greenhouse gases. Hydropower has long been considered a renewable alternative, but the current technique for harnessing that power, i.e. damming rivers, can be extremely damaging to ecosystems, and almost every suitable place in the world has already been tapped. Now scientists and engineers are learning to harness the endless power of ocean waves, promising electricity generation with minimal environmental effects. None of the current wave energy technologies generate greenhouse gases or pollution.
Many different technologies have been developed to convert waves into electricity. Two of the most promising technologies take advantage of the vertical movement of waves. The first of them is a generator of buoys or absorption points. These layouts contain a fixed component and a floating component. The waves move the floating component up and down relative to the fixed component, driving one of several types of systems. An arm protruding from the buoy can be attached to a crank, which then turns a mechanical generator. Similarly, self-contained hydraulic pumps can be actuated by the movement of the buoy and then drive a hydraulic motor. Yet another system uses motion to pump pressurized seawater. This pressurized seawater can then be pumped through a turbine or even pumped ashore to power osmotic desalination processes. Buoy generators are currently being used at various locations. Finavera has projects in the waters of Portugal, Africa and the North Pacific waters of the US and Canada. Oregon State University has a pilot project off the coast of Reedsport, and CETO has a project running off Western Australia. The second type of design that takes advantage of vertical movement is called a fader, also known as surface tracking technology. Pelamis devices have cornered this section of the market and there are virtually no other technologies available. These generators derive their name from Pelamis platuris, a yellow-bellied sea snake, an apt name considering the generator’s long, narrow design and its rocking motions. The machine consists of long floating tubes connected by two arms at movable joints. As waves change the angle of two tubes relative to each other, hydraulic pumps compress and stretch, driving hydraulic generators. These Pelamis generators are being used in the world’s first commercial wave park, the Aguçadora Wave Park off Portugal, and also in the 3MW wave park off the coast of Scotland.
The remaining wave harnessing technologies, called terminators, take advantage of the horizontal motion of waves. The oscillating water column design uses the movement of a wave-driven piston to drive pressurized air through a turbine, which in turn drives a generator. Overflow is suggested for both onshore and offshore use, and involves channeling wave water into elevated reservoirs. Gravity then pulls the water down, where it is channeled to drive a turbine, just like in hydroelectric dams. The most famous of this type is the Wave Dragon off the coast of Denmark. The Wave Dragon includes two arms that channel and amplify the waves before driving the water into the tank. Aquamarine Power has developed two very innovative designs, the Oyster and the Neptune. The oyster is a large plate mounted on the seabed, whose back and forth movement is resisted by hydraulic arms that operate a hydraulic generator. The Neptune uses bi-directional underwater turbines to harness tidal energy.
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