Ocean thermal energy conversion
Although it has challenges to overcome, OTEC has the potential to provide a consistent and sustainable source of clean energy, particularly in tropical regions with access to deep ocean water.OTEC uses the ocean thermal gradient between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity.This eventually led to an effort by Lockheed, the US Navy, Makai Ocean Engineering, Dillingham Construction, and other firms to build the world's first and only net-power producing OTEC plant, dubbed "Mini-OTEC"[16] For three months in 1979, a small amount of electricity was generated.Later, a team led by Dr. Bharathan at the National Renewable Energy Laboratory (NREL) developed the initial conceptual design for up-dated 210 kW open-cycle OTEC experiment ([24]).It was renamed the Net Power Producing Experiment (NPPE) and was constructed at the Natural Energy Laboratory of Hawaii (NELH) by PICHTR by a team led by Chief Engineer Don Evans and the project was managed by Dr. Luis Vega.[26] In 2006, Makai Ocean Engineering was awarded a contract from the U.S. Office of Naval Research (ONR) to investigate the potential for OTEC to produce nationally significant quantities of hydrogen in at-sea floating plants located in warm, tropical waters.In July 2011, Makai Ocean Engineering completed the design and construction of an OTEC Heat Exchanger Test Facility at the Natural Energy Laboratory of Hawaii.[41][failed verification] Early in April 2018, Naval Energies shut down the project indefinitely due to technical difficulties relating to the main cold-water intake pipe.[49] The mini OTEC vessel was moored 1.5 miles (2.4 km) off the Hawaiian coast and produced enough net electricity to illuminate the ship's light bulbs and run its computers and television.OTEC plants require a long, large diameter intake pipe, which is submerged a kilometer or more into the ocean's depths, to bring cold water to the surface.Also, the mixed discharge of cold and warm seawater may need to be carried several hundred meters offshore to reach the proper depth before it is released, requiring additional expense in construction and maintenance.One way that OTEC systems can avoid some of the problems and expenses of operating in a surf zone is by building them just offshore in waters ranging from 10 to 30 meters deep (Ocean Thermal Corporation 1984).[54] To avoid the turbulent surf zone as well as to move closer to the cold-water resource, OTEC plants can be mounted to the continental shelf at depths up to 100 meters (330 ft).As an alternative to a warm-water pipe, surface water can be drawn directly into the platform; however, it is necessary to prevent the intake flow from being damaged or interrupted during violent motions caused by heavy seas.[55] Because OTEC facilities are more-or-less stationary surface platforms, their exact location and legal status may be affected by the United Nations Convention on the Law of the Sea treaty (UNCLOS).[62] OTEC projects under consideration include a small plant for the U.S. Navy base on the British overseas territory island of Diego Garcia in the Indian Ocean.Ocean Thermal Energy Corporation (formerly OCEES International, Inc.) is working with the U.S. Navy on a design for a proposed 13-MW OTEC plant, to replace the current diesel generators.[66] Lockheed Martin's Alternative Energy Development team has partnered with Makai Ocean Engineering[67] to complete the final design phase of a 10-MW closed cycle OTEC pilot system which planned to become operational in Hawaii in the 2012–2013 time frame.[69] On April 13, 2013, Lockheed contracted with the Reignwood Group to build a 10 megawatt plant off the coast of southern China to provide power for a planned resort on Hainan island.[34] South Korea's Research Institute of Ships and Ocean Engineering (KRISO) received approval in principle from Bureau Veritas for their 1MW offshore OTEC design.Dr. John P. Craven, Dr. Jack Davidson and Richard Bailey patented this process and demonstrated it at a research facility at the Natural Energy Laboratory of Hawaii Authority (NELHA).[98] Ocean thermal gradient can be used to enhance rainfall and moderate the high ambient summer temperatures in tropics to benefit enormously the mankind and the flora and fauna.Creating high pressure zones by artificial upwelling on sea area selectively can also be used to deflect / guide the normal monsoon global winds towards the landmass.[99] It would also lead to enhanced carbon sequestration by the oceans from improved algae growth and mass gain by glaciers from the extra snow fall mitigating sea level rise or global warming process.[citation needed] A rigorous treatment of OTEC reveals that a 20 °C temperature difference will provide as much energy as a hydroelectric plant with 34 m head for the same volume of water flow.[103] A previous Final Environmental Impact Statement (EIS) for the United States' NOAA from 1981 is available,[105] but needs to be brought up to current oceanographic and engineering standards.[106] Most recently, NOAA held an OTEC Workshop in 2010 and 2012 seeking to assess the physical, chemical, and biological impacts and risks, and identify information gaps or needs.[46] A 1977 study in which mock heat exchangers were exposed to seawater for ten weeks concluded that although the level of microbial fouling was low, the thermal conductivity of the system was significantly impaired.Aluminium tubing slows the growth of microbial life, although the oxide layer which forms on the inside of the pipes complicates cleaning and leads to larger efficiency losses.[117] In 2014 Liping Liu, Associate Professor at Rutgers University, envisioned an OTEC system that utilises the solid state thermoelectric effect rather than the fluid cycles traditionally used.
renewable energytemperature differencewarm surfacecold depthsheat engineelectricityclean energysustainable sourcetropicaldeep ocean waterocean thermal gradientseawaterscapacity factorbase loadSouthern Oceanthermohaline circulationUpwellingdownwellingrenewable energy resourcesrefrigerantsammoniaR-134aRankine cycleseawaterfresh waterSaga UniversityGeorges ClaudeJacques Arsene d'ArsonvalphysicistpressureturbineAbidjanTokyo Electric Power CompanyKeahole PointHawaiiNatural Energy Laboratory of Hawaii AuthorityKona coastUnited States NavyCuraçaoKreithMax Jakob Memorial AwardIts governmentOffice of Naval ResearchNatural Energy Laboratory of HawaiiDavid Igetemperaturetropicswave poweremerging technologythermally efficientCarnot efficiencyheat exchangerelectrical generatordesalinizeddrinking waterirrigationaquaculturegas liftvapor lifthydroelectric turbineNational Renewable Energy Laboratorydesalinated waterheat pipeHydrocarbonselectrolysismariculturesurf zoneUnited Nations Convention on the Law of the Seaartificial islandsfisheriesseabed miningInternational Seabed Authoritycost of electricitykilowatt hourInternational Energy AgencySolar PVwind powerpetroleummethane hydratesU.S. NavyDiego GarciaIndian OceanLockheed MartinNaval Facilities Engineering CommandDepartment of EnergyHainandeepwater drillingsurface condensersInterContinentalBora Boratemperate climatessubtropicssalmonlobsterMicroalgaeSpirulinaabaloneoystersHydrogentrace elementsmagnesiumuraniumflora and faunasea surface temperaturesglobal windscarbon sequestrationmass gain by glacierssea level riseglobal warmingTropical cyclonesfloating wind turbinedeep seadraft tubeanchored to the sea bedpontoonsbattleship Bismarckinsolationclearness indexBeer–Lambert–Bouguer's lawdifferential equationfalls exponentiallythermal convection currentsconductionsubtropicalequatorialsaturation pressures