By Samuel Lewis

Harnessing the vast power of the oceans' 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 quantities of greenhouse gasses. Hydropower has long been considered a renewable alternative, but the current technique for harnessing that power, namely damming rivers, can be extremely damaging to ecosystems, and nearly all of the suitable locations in the world have already been tapped. Now scientists and engineers are learning to harness the unending power of ocean waves, promising electricity generation with minimal environmental effects. None of the current wave power technologies create greenhouse gasses or pollution.

Many different technologies have been developed to convert waves into electricity. Two of the most promising technologies take advantage of the vertical motion of waves.

The first of these is a buoy or point-absorber generator. These designs contain a fixed component and a floating component. Waves move the floating component up and down in relation 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 driven by the motion of the buoy, then driving a hydraulic motor. Yet another system uses the motion to pump pressurized sea water. This pressurized sea water can then be pumped through a turbine or even pumped onshore to drive osmotic desalination processes.

Buoy generators are currently being used in several locations. Finavera has projects in waters off 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 motion is called an attenuator, also known as surface-following technology. Pelamis devices have cornered this section of the market, and virtually no other technologies are available. These generators derive their name from Pelamis platuris, a yellow-bellied sea snake, a fitting name considering the generator's long, narrow design, and its oscillating movements. The machine consists of long, buoyant tubes connected by two arms at movable joints. As the waves change the angle of two tubes with respect to each other, hydraulic pumps are compressed and stretched, driving hydraulic generators. These Pelamis generators are being used in the world's first commercial wave farm, the Aguçadora Wave Park off Portugal, and also in the 3MW wave farm off the coast of Scotland.

The remaining wave-harnessing technologies, referred to as terminators, take advantage of the horizontal motion of waves. The oscillating water column design uses the motion of a wave-driven piston to drive pressurized air through a turbine, which in turn drives a generator. Overtopping is suggested for use either on or offshore, and involves funneling wave water into elevated reservoirs. Gravity then pulls water back downward, where it is funneled to drive a turbine, much as in hydropower dams.

The most famous of this type is the Wave Dragon off the coast of Denmark. The Wave Dragon includes two arms that funnel and amplify the waves before driving the water into the reservoir. Two very innovative designs, the Oyster and the Neptune, have been developed by Aquamarine Power. The oyster is a large plate mounted to the sea floor, whose back-and-forth motion is resisted by hydraulic arms which run a hydraulic generator. The Neptune uses underwater, bi-directional turbines to harness tidal energy.

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