Specially built seagoing vessels can also capture the energy of offshore waves. The rise and fall of the float stretches and relaxes the hose, which pressurizes the water, and, in turn, rotates a turbine. Other offshore devices use hoses connected to floats that ride the waves. Sophisticated mechanisms-like the Salter Duck-use the bobbing motion of the waves to power a pump that creates electricity. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet). Wave energy can be converted into electricity through both offshore and onshore systems. Cold water passing through a condenser, containing the vaporized working fluid, turns the vapor back into a liquid, which is then recycled through the system. The expanding vapor drives a turbine attached to a generator, which produces electricity. In a closed-cycle system, heat transferred from the warm surface water causes a working fluid to turn to vapor. There are three types of ocean thermal energy conversion processes: closed-cycle, open-cycle, and hybrid-cycle. Ocean Thermal Energy ConversionĪn ocean thermal energy conversion system is made up of several key components including: This section provides information on ocean energy systems and reviews the three main types of ocean thermal energy conversion processes. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Ocean Energy Technology Basics. Further general information is available from the U.S. This overview is intended to provide specific details for Federal Agencies considering ocean energy as part of a major construction project. The International Energy Agency has a group dedicated to Ocean Energy Systems which has further information and analyses on various types of ocean energy. The construction costs are high and lengthen payback periods. A tidal dam might be identical to a river dam, but it will produce less than half the amount of electricity. Although tides are more predictable than wind energy or solar power, it is still intermittent and expensive. Tidal dams create many of the same environmental concerns as damming rivers, such as restricting fish migration and causing a buildup of silt. The Rance Tidal Power Station is located on the Rance River in France, and was the first tidal power station starting operation in 1966. Some of the oldest ocean energy technologies use tidal power, but there are currently no tidal power plants in the United States. Wave technology is still being developed, but will eventually become competitive with wind and solar. Construction of the nation's first wave-energy farm began off the Oregon coast in 2010, with completion expected by 2012. There are a few areas where wave power may prove desirable, but wave energy is intermittent and variable. The world's first commercial wave energy plant, at 0.5 megawatts (MW) of power, was developed in Scotland. The first known patent to use energy from ocean waves was filed in 1799 in Paris, France. Wave power devices extract energy directly from the surface motion of ocean waves or from pressure fluctuations below the surface. The National Oceanic and Atmospheric Administration released a paper on this, titled Technical Readiness of Ocean Thermal Energy Conversion (OTEC). The main attraction is that it produces power day and night, and it does not fluctuate like solar or wind. However, it requires costly infrastructure to deliver cold water from the depths, and it doesn't produce much power compared to the amount of equipment required. It provides air-conditioning for buildings, produces base load electrical energy, and has significant potential to provide clean, cost-effective electricity for the future. Ocean thermal energy conversion is a resource for onshore and near-shore mariculture operations. The laboratory has become a leading test facility for this type of technology. Hawaii is the best location in the United States for ocean thermal energy conversion due to the warm surface water, high electricity costs, and access to very deep, cold water. The United States became involved in 1974, establishing the Natural Energy Laboratory of Hawaii Authority (NELHA). Ocean thermal energy conversion attempts began in the 1880s, but the first plant was not built until 1930 in Cuba. Tidal energy is a form of hydropower that derives its energy from the motion of large bodies of water that make up the tides. A process called ocean thermal energy conversion generates electricity using the difference in temperature between the warm surface of the ocean and the cold ocean depths. The ocean covers more than 70% of the earth's surface and has the ability to produce two types of energy: thermal energy from the sun's heat, and mechanical energy from the waves and tides.
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