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OWOE - Other Renewables Energy - What is an ocean thermal energy conversion plant?
  Figure 1 - Schematic of Offshore Thermal Energy Conversion Plant (Makai Ocean Engineering)
Figure 1 - Schematic of Offshore Thermal Energy Conversion Plant (Makai Ocean Engineering)
Figure 2 - How OTEC Works (Makai Ocean Engineering)
Figure 3 - The Ocean Energy Research Center in Kailua-Kona, Hawaii (Makai Ocean Engineering)
Video - Makai Ocean Engineering - The Future of Renewable Energy using Ocean Thermal Energy Conversion
What is an ocean thermal energy conversion plant?

Ocean Thermal Energy Conversion (OTEC) is a process that can produce electricity by using the temperature difference between deep cold ocean water and warm tropical surface waters. OTEC plants pump large quantities of both cold and warm seawater to run a turbine and produce electricity. Figure 1 illustrates a future OTEC power plant that will have the potential to generate 100 MW of clean, renewable energy. Figure 2 illustrates a basic closed-cycle OTEC plant. As opposed to most steam electric generating stations which are based on boiling water for steam, OTEC utilizes ammonia as the working fluid. Ammonia's boiling temperature is low enough that warm seawater can vaporize the fluid. Warm seawater passes through an evaporator and vaporizes the ammonia, which then passes through a turbine which turns a generator to make electricity. The ammonia vapor then passes through the condenser where the cold seawater cools it back into a fluid. The liquid ammonia is pumped back to the evaporator to repeat the cycle.

The Naval Facilities Engineering Command (NAVFAC) , the Office of Naval Research (ONR) and the State of Hawaii have jointly participated in construction of a new 100 kW OTEC Heat Exchanger Test Facility on the big island of Hawaii. Makai Ocean Engineering was contracted to design and build the facility which is shown in Figure 3. In August 2015 it became the first OTEC plant to connect to a US grid.

The problem with this renewable energy source is cost. At present, OTEC plants can be built that will be economically attractive to islands such as Hawaii, Puerto Rico and Guam, which have electrical rates just above twenty cents per kWh becasue of the need to burn oil for the majority of their electricity needs. As OTEC technology matures and development costs can be reduced, economic viability should improve, and it is anticipated that OTEC could become economically attractive in the southeast US.

By one estimate the global potential for OTEC could provide four times the total electrical power needs of the entire planet.

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