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Ocean Powers (Tidal and Wave)

Ocean power is an often overlooked, but rapidly growing energy alternative which takes advantage of the vast quantities of potential energy stored in the ocean. Gravitational influences between the sun, earth, and moon create a tremendous store of this potential energy in the water and this energy is able to be captured through technologies which utilize the waves and tides of the ocean. Tidal power captures water at high tide and releases it at low tide, the flow of which drives a turbine to generate electricity. Wave power utilizes the oscillating motion of incoming and outgoing waves to drive turbines that generate electricity. A third technology, ocean thermal energy conversion, uses the difference in temperature between warm surface water and cold deep ocean water to channel the water through turbines that generate electricity.

Although wave and tidal power are the least developed of the renewable energy alternatives, there have been a number of interesting developments throughout the world. In New York City, for example, turbines are being submerged in the East River to generate electricity from rapid tidal currents. Utilizing lessons learned from wind turbine designs, the systems in the East River utilize three-bladed turbines which are five meters in diameter and made by Verdant Power of Arlington, Virginia. The project is just one of 25 approved and 31 pending sites proposed to the Federal Energy Regulatory Commission (FERC) in the past four years [1]. Other examples of tidal applications include La Rance in Normandy which generates 240MW of electricity, and Halifax utility in Nova Scotia which generates 20MW of electricity.

There are also many examples of wave power applications, including Island of Islay located off Scotland’s west coast, which utilizes a wave power system which generates 250 kW of electricity. In the UK, there are plans to build a 3 MW wave power system. Each unit in this system will have similar output to a modern wind turbine and the system will generate enough electricity to power 2,000 homes. Portugal claims the world’s first commercial wave farm, with construction started in 2006 and goals to be completed by 2009. When completed, the farm will be the world’s largest with a capacity of over 3MW generated by four Pelamis machines. The Pelamis machine is a series of cylindrical segments connected by hinged joints. As waves run down the length of the device and actuate the joints, hydraulic cylinders incorporated in the joints pump oil to drive a hydraulic motor via an energy-smoothing system. Electricity generated in each joint is transmitted to shore by a common sub-sea cable [2].

Ocean Power Technologies, located in New Jersey, has recently unveiled a new and very interesting technology design dubbed PowerBuoy. PowerBuoy is a modular, ocean-going buoy that converts the potential energy of rising and falling of waves to mechanical energy and then to electricity. Currently the systems have a capacity of 40 KW, but the company is designing systems which will deliver up to 500 KW.

Wave and tidal power face many technological challenges including developing devices which can survive storm damage and saltwater corrosion, creating devices that can efficiency convert wave motion to electricity, furthering technological advancements to reduce the cost of electricity generated from the systems, gaining commitment of governments and local authorities, the development of suitable approaches to grid connection, and the willingness of the financial community to recognize the key role of wave and tidal energy technologies [2].