Electricity production from ocean sources is from four different categories:

  1. Ocean thermal
  2. Ocean current
  3. Ocean wave
  4. Ocean tidal

Ocean thermal makes use of temperature gradients in a thermal (Rankine) cycle process. Unfortunately, ocean thermal requires the use large plants because of the low thermal efficiency, and hence, a large capital investment is needed for such plants. For example, at the Caribbean Sea, tropic waters meet and flow over artic waters with a temperature difference of 35°-40°F over a 1500-2000 ft vertical separation. Based on 35°F temperature difference, the Carnot cycle (best possible) efficiency is low, i.e., approximately 6%. The actual efficiency is 2-3% since the water must be pumped and there are thermal losses. Example plants built include a small 40kWe plant in Cuba (1926), and a 50kWe plant off Hawaii.

Ocean current uses the kinetic energy (like the wind) of the water current in locations like the Gulf Stream. Turbines are anchored to the sea floor.

Ocean wave harnesses the bouyancy of the waves. In 1909, ocean wave power was used to light lamps on the Hunington Beach Wharf until a storm carried the apparatus out to sea.

Ocean tidal power harnesses the kinetic energy (potential energy) of the tides. Most concepts employ a dam approach with hydraulic turbines. A drawback of tidal power is its low capacity factor, and it misses peak demand times because of 12.5 hr cycle of the tides. The total world potential for ocean tidal power has been estimated at 64,000 MWe. The 25-30 ft tidal variations of Passamaquoddy Bay (Bay of Fundy) have the potential of between 800 to 14,000 MWe. Example tidal-electric plants have been built including a 2 MWe Russian plant, a 240 MWe (1966) installation in France, and the Canadians have a 20 MWe (1984) tidal-electric plant.

Last updated: November 7, 1997

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