Renewables Technologies May Expand Geographic Range of OTEC Plants

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Written By: Emma Websdale

New studies reveal that the incorporation of other renewable energy technologies into Ocean Thermal Energy Conversion (OTEC) plants can significantly expand their geographic range of operation – enabling more regions to produce their own clean energy and drinking water. 

The potential capacity of power generation using the ocean temperature difference is around 1.1 trillion kilowatts (KW) – enough energy to serve the world’s total energy demand 100 times over. Ocean Thermal Energy Conversion (OTEC) technologies tap into this abundant and sustainable resource.

Currently, data from the National Renewable Energy Laboratory (NREL) of the United States Department of Energy (DOE) list at least 68 countries and 29 territories as having the OTEC thermal resources required to power OTEC plants (a temperature difference between warm surface water and cold deep water of at least 20°C). These areas run in a band along the equator and are in tropical regions within 20o north and south latitude – areas that often heavily depend on fossil fuels, making them vulnerable to volatile energy prices that can reach as high as US$0.30-$0.60/kWh.

OTEC plants -using the tropical region’s abundant ocean thermal resources, can satisfy two crucial needs -clean drinking water and clean energy. This production can directly relieve high fossil fuel prices, carbon dioxide emissions and water shortages.

Regions situated outside of this tropical zone also face problems of high-cost fossil fuel and stressed water resources. Fortunately, scientists and developers are researching methods that would allow OTEC plants to operate outside these ideally located thermal regions.

For example, using computer models, Paola Bombarda of Milan’s Polytechnic University has proved that solar collectors (mechanisms including lenses or tubes that trap heat) can significantly increase the power output of OTEC plants. Utilizing solar collectors, OTEC plants can heat up warm ocean water reducing the overall temperature gap required to operate the plant.

Bombarda’s results, published in the Journal of Engineering for Gas Turbines and Power, showed that by using solar collectors in a closed OTEC cycle, the performance of daytime electricity output from OTEC plants could be increased by approximately 30%, making them better adapted to less tropical areas.

In other research, engineers from the Korean Ocean Research & Development Institute (KORDI) in Goseong-gun modified a 20-KW demonstration OTEC plant. These engineers used heat from solar power, wind farms and waste incineration plants to preheat the incoming surface water before it entered the plant. Preheating can make OTEC viable in countries like South Korea where temperatures during the winter slip below the 20oC thermal resource threshold.

Engineers at KORDI are also currently investigating the possibility of adding geothermal energy (tapping into energy that is trapped deep underground) to the plant, which could enable them to heat water for OTEC use on a 24-hour basis.  If these amendments are successful, the equatorial waistband for productive OTEC plants will expand greatly.

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