Offshore Power Generation Using Ocean Thermal Energy Conversion
In just a single day, the sun provides raw energy to Earth more than what the entire planet needs in a single year.
A significant portion of this “wasted” energy is absorbed by the world’s oceans. This huge amount of thermal energy warms the surface up, creating a temperature difference between the water above and the water deep below.
Suppose that we treat the warm part of the ocean as a hot reservoir, and the cold part of the ocean as a cold reservoir. Could we design a heat engine that could generate power from the ocean? The answer is yes, and this is another alternative type of renewable, green energy that is called ocean thermal energy conversion (OTEC).
The Ocean as Both Evaporator and Condenser
There are many configurations that can be used for ocean thermal energy conversion, although the basic process remains relatively simple. As it runs on a heat engine, all you need to do is boil a liquid using the warm ocean water and turn it to steam. The generated steam would then power a turbine that would produce electric energy. Afterwards, the heated liquid would then be sent to the condenser, to be cooled down by the colder ocean water deep below. Propane is the commonly proposed liquid to be used in this system, as it has a very low boiling point of -42 °C (−44 °F).
In essence, a power plant that uses ocean thermal energy conversion uses a single body of water both as the evaporator and the condenser.
Considerations When Constructing Ocean-Based Power Plants
Designing and constructing a plant that uses ocean thermal energy conversion would have to depend on a number of fundamental factors. The power plant has to be situated in an area where it is deep enough AND near enough to the area where the power would be needed. The optimal depth is about 3000 feet (914 meters), although installations could be placed in areas that are shallower.
Next, it has to make do with the environmental hazards that are usually present in sea-based and off-shore installations. For example, floating ocean thermal energy conversion facilities would have to adapt to the difficulties in setting up and maintaining long and deep water cables.
Practicality and Economic Issues
You may have thought about this already upon reading the words “ocean” and “energy”, but ocean thermal energy conversion is only effective when the community or facility is somewhere near the coastlines. Also, it is worth noting that choosing the proper location may not just be based on “where it is deep enough”, but may also be based on how generally safe the location is.
Furthermore, ocean thermal energy conversion plants must also be constructed with the idea of resilience in mind. It should be sturdy enough to ride the turbulent seas while providing uninterrupted power for the city or community, even during extreme changes in weather (like those weather-resistant off-shore oil rigs).
Current and Future Plans and Proposals
Small island nations are the ones who would most likely see ocean thermal energy conversion as a good and economically viable alternative to fossil fuels.
In Hawaii, a pilot project is underway to construct a 10 megawatt closed system power plant that uses ocean thermal energy conversion. The project is headed by Lockheed Martin’s Alternative Energy Department, and is scheduled to be completed around 2012-2013.
Puerto Rico is blessed to be situated in an important “junction point” between the world’s major ocean currents. Almost each corner of the island can be installed with an ocean thermal energy conversion plant, with its south east area having access to the hottest and coldest ocean water within just 2 miles off shore. It has been hypothesized that the installation of thirty 100 megawatt floating plants could supply all the energy needed by the country.
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