What is Water Energy?
Hydropower – Ocean Thermal Energy Conversion (OTEC) – Tidal – Wave Power
Videos: Hydropower Ocean Power Wave Power
How do we Harvest Energy from Water?
Ocean energy draws on the energy of ocean through two basic ways. One way is thermal energy. Thermal energy is provided by the sun. We harness the energy that is stored in the surface layers of the ocean. The second way is mechanical energy which come from tides and waves.
Hydropower Energy
The term geothermal comes from the Greek geo meaning earth and therine meaning heat thus geothermal energy is energy derived from the natural heat of the earth. The earth’s temperature varies widely, and geothermal energy is usable for a wide range of temperatures from room temperature to well over 300° F. For commercial use, a geothermal reservoir capable of providing hydrothermal (hot water and steam) resources is necessary. Geothermal reservoirs are generally classified as being either low temperature (<150° C) or high temperature (>150° C). Generally speaking, the high temperature reservoirs are the ones suitable for, and sought out for commercial production of electricity. Geothermal reservoirs are found in “geothermal systems” which are regionally localized geologic settings where the earth’s naturally occurring heat flow is near enough to the earth’s surface to bring steam or hot water to the surface. Examples of geothermal systems include the Geysers Region in Northern California, the Imperial Valley in Southern California, and the Yellowstone Region in Idaho, Montana, and Wyoming.
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Ocean Thermal Energy Conversion (OTEC)
The water at the surface of the ocean is warmer than the water at deeper depths. This temperature difference can be used by Ocean Thermal Energy Conversion (OTEC) systems to generate electricity. Warm water from the surface and cold water pumped from deeper depths can be utilized by three types of OTEC systems. Open-cycle OTEC uses the seawater itself as the working fluid by boiling it at low pressures. This produces low-pressure steam that passes through a turbine generator to produce electricity. The cold water is used to condense the vapor back to a liquid. Closed-cycle OTEC uses warm surface water to vaporize a low-boiling point working fluid, such as ammonia. The expanding vapor of the working fluid drives a turbine generator to produce electricity. The cold water is used to condense the vapor back to a liquid, which is recycled by the system. Hybrid systems employ both closed-cycle and open-cycle systems. OTEC systems are currently in the research and demonstration stage of development.
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Tidal Energy
There are basically two methodologies for creating tidal power: the use of tidal dams or ocean currents. Dams are based on using a barrage at a bay or estuary with a large tidal range. Power is generated primarily at ebb tides as the barrage creates a significant head of water, much like a hydroelectric dam.
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Wave Energy
Ocean waves are caused by the wind as it blows across the sea. Waves are a powerful source of energy. The problem is that it’s not easy to harness this energy and convert it into electricity in large amounts. Thus, wave power stations are rare.
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