Rough ocean Photo:
The ocean is a harsh place. Salt water can corrode electronics, violent storms batter equipment and the waves themselves punish moving parts. So, when it comes to WECs, new technologies are often developed with an eye towards simplicity. One example of this is the Oscillating Water Column (OWC).
While jogging along the surf- smacked shores of Sydney’s famous Bondi Beach, Australian inventor Tom Denniss would talk to colleagues about a simple device that could convert the ocean’s kinetic energy to electricity. His chats became research, and turned into the OWC, manufactured by Oceanlinx, the company he founded.
An OWC functions like a giant air piston with a long tube capped by a generator. As waves enter the bottom of the tube, they force the air upwards and turn a turbine which produces power. As the wave re- cedes, air is sucked back through the tube, continuing to turn the turbine – the one moving part in the system.
To maximise efficiency, the OWC uses a sensor to sense the direction of the air flow and send an electronic signal to the turbine to change its blade pitch. "This enables an optimal angle of air flow over the blades. Obviously, the blades change in direction, but they also change in speed. So the turbine changes its characteristics to optimally extract the maximum amount of power," says Denniss.
Oceanlinx has plans to install its systems in the waters of Namibia and Australia as well as off the coast of Maui, Hawaii, where it is predicted that just three units could power up to 4,000 homes and, compared to coal, will prevent 9,000 tonnes of carbon dioxide from entering the atmosphere per annum.
Wonder of Water
Tapping the limitless power of the oceans has a clear advantage over other types of renewable energy:
• because of their density, waves are more powerful than air currents, so smaller devices can be used to harness the energy.
• The seas are constantly in motion and therefore produce energy around the clock, unlike solar and wind systems which are daylight and/ or weather dependent.
• Communities often fight alternative-energy arrays because they don’t like the aesthetic effect. Many ocean devices can be put far enough out at sea to stay out of sight.
• A lot of cities do not have any land on which to build windmills but are near bodies of water. Wave energy converters and sea windmills do not take up space that could be used for housing or farming.
Making energy from water cuts out nasty emissions. The prototype of Oceanlinx’s Oscillating Water Column currently operating off the coast of sydney, Australia, produces zero emissions of both carbon dioxide and sulphur dioxide. It is estimated that if the amount of electricity produced by a coal-fired plant is generated instead using OWCs, that one billion tonnes less of carbon dioxide will be spewed into our air in one year.
Every day, the surface waters of our tropical oceans soak up the amount of heat from the sun that could be produced by 250 billion barrels of oil. yet just below the surface, the water quickly cools. When the temperature between the upper layers of the sea differs from the deeper water by 20 degrees Celsius, Ocean Thermal Energy Conversion (OTEC) systems become viable. These work by using the tropical waters to vaporise liquids with low boiling points, such as ammonia or propane. As the liquid becomes vapour, it turns a turbine and is then condensed back to a liquid using the deeper, cooler water. The process then begins again. The us military is planning two OTEC facilities – one near Diego garcia in the Indian Ocean, the other off the Marshall Islands in the pacific.
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