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Published on September 23rd, 2011 | by Breath on the Wind

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Ocean Thermal Energy Conversion



OTEC is a technology that has been discussed and extensively researched until recently by the US government. Now OTE Corporation (@OTEcorporation on twitter) and Bahamas Electricity Company, announced that they signed a memo of understanding for the further development of the world’s first two commercial ocean thermal energy conversion (OTEC) plants, sited in the Bahamas. OTE Corporation has been in the news this year as it fills corporate positions. With the announcement of this agreement, it begins its core mission to bring OTEC to the nearly 100 tropical regions around the world, where land-based commercial OTEC power plants are now an economically viable solution.

Tropical Islands

Islands present a special problem for electric power. You may have the sun and some wind, but these power sources are not constant. On the mainland, we can use the grid as a buffer between supply and demand, but islands have to resort to expensive energy storage or imported supplies of fossil fuels. And so, it is not surprising that we find electrical storage batteries and some of the most expensive electric rates on islands. Tropical islands also have another largely untapped resource. This is the difference between surface water temperatures and that found in the deep ocean.

How It Works

A typical power plant uses a heat source to boil water. The heat source could be coal, nuclear or even a solar collector (Power tower or trough CSP.) Steam then drives a generator through a turbine. This is the Rankine cycle.

OTEC uses a smaller difference in ocean temperatures to generate electricity. It is an adaptation of the technology used in ice houses, solar ponds, and Dry Well Geothermal: the organic Rankine Cycle. In this instance, a different fluid is substituted for water. Ammonia is often used due to its lower boiling point. To cool the liquid and restart the cycle, deep ocean temperatures are used. Where does this energy actually originate? It is the Sun that heats the ocean surface and is being harnessed by OTEC.

History

OTEC was first considered almost 140 years ago. In 1974, the US, through the National Energy Research Labratory (NREL), was conducting the world’s most intensive research at a site in Hawaii.

Advantages

Unfortunately, while the organic rankine cycle allows us to use lower temperatures it is not as efficient as using super-heated steam. Inefficiency at first may appear to put the OTEC at an economic disadvantage to other forms of power generation. However, a facility can make up for this deficiency by using additional economic streams including:

1. Supplying potable fresh water

Theoretically, an OTEC plant that generates 2-MW of net electricity could produce about 4,300 cubic meters (14,118.3 cubic feet) of desalinated water each day.

2. In addition to providing power and water, OTE Corporation can provide cooling to areas near its plants powered by the deep cool ocean. This may simply be very economic cooling for nearby buildings or may be promoting aquaculture and unusually temperate plants grown in a tropical environment:

OTEC technology also supports chilled-soil agriculture. When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics.

What is done on land can also be done with aquaculture using cool water to support lobsters and other species not normally grown in the tropics.

Future Possibilities

Islands are not the only places that need water. California has already built desalination plants to augment its water supply. Any tropical coastal region could use OTEC. OTEC is a clean, renewable energy source that has the potential to free many economies from their dependence on oil.

Photo Credits: OTEC
For additional reading/sources: NREL overview

 

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About the Author

We share this World; its past, present resources and our combined future. With every aspiration, the very molecules we use for life are passed to others through time and space so that each of us may be considered a Breath on the Wind. This part of the world's consciousness lives in NYC; has worked in law, research, construction, engineering; has traveled, often drawn to Asia; writes on Energy and Electric Vehicle issues and looks forward to all your comments.   "If you would persuade, you must appeal to interest rather than intellect." -- Benjamin Franklin



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  • Dietrich Von Bacon

    Well this all sounds super fantastic. How much power will it take to pump all the water? Would there be an energy deficit by just moving the water alone? Take into account the minor change in temperature and enthalpy along with mechanical losses and I have a hard time seeing this come to fruition. Good luck to them but I wouldn’t put my money into this idea.

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  • Wayne Baumunk

    Wayne Baumunk, Guam Island, crmcsrvc@teleguam.net Tinian Island sits on the edge of the Marians Trench, cold seawater is withing 1KM, land bassed 5MW unit would power most of the island. Generated fresh water could be used by residents. US Military could use gathered data.

  • http://www.facebook.com/people/Bruce-Miller/100000952005408 Bruce Miller

    The creation of the poisons from the fission of Uranium is far too dangerous for humanity. It must be stopped – world wide – but not by force, rather by reason, and the freely giving of Thorium fueled fission technologies for cheap energy for all mankind. Will China once she perfects this new ‘Fire” do just that, as she builds her Pan-Eurasian Empire? Will she burn off the dangerous “spent fuel” from Uranium fission, reducing it to harmless substances in only three hundred years, and save mankind from the voracious sociopaths in America still flogging their death to humanity akin to the Fuckoshima experience, to an unsuspecting world? Solar, Wave, Wind, hydro, Tidal, Geothermal, Gobar gas, bio-mass, now this Ocean thermal free safe domestic energy can replace the horrendous American lifestyles with a softer quieter way, now that technologies have risen , humanity has grown, and as we speak, we see this change occurring on the streets of even the U.S.A. Will she redeem herself, suffer the gut wrenching paradigm shift away from McMansions and SUV’s towards public transportation, medical care with communal leverage, and an economics that shares the wealth melodramatically – Yes it is inevitable, and by the hand of good people, not government decree.

    • Breath on the Wind

      Great comment Bruce. I would agree that for change to be truly effective it must come from within each of us.

      But you might take a breath. Sometimes change is inspired also by a change in the environment: our laws, social standards and changes in our physical environment.

      • Anonymous

        Change, in the way we create electricity and power our vehicles, is likely to come via economics.

        Coal is an expensive way to make electricity (if you add in the tax dollars paid for health issues and the extra health insurance premiums).

        New nuclear is very expensive.

        Oil is expensive and will continue to get more expensive.

        Wind is one of the two cheapest ways to make electricity, if we’re talking new generation and not power from older paid off plants. Natural gas is the other cheapest way, but that price will rise.

        Solar is rapidly dropping in price and should become as cheap, or cheaper, than wind.

        Running an EV on electricity costs about 1/4th as much as running the average US car on gasoline.

        It will take a little more time to get EV batteries down in price, but we should hit a point where EVs are cheaper than gas/diesel cars to purchase.
        Over the next few years economics alone will move us from fossil fuels to
        renewables. Of course, we need to speed that transition via
        social/political means because we are creating a major problem for the
        entire planet if we keep burning fossil fuels.

        A bit of social/political push in terms of putting some sort of price on
        carbon and keeping subsidies in place for renewables/EVs would speed us to
        the point where economics, alone, will finish the job.

  • http://twitter.com/adrianslew Adrian Slew

    Anyone know if Thailand is considering this technology? Might be good for the country.

    • Breath on the Wind

      This company is very new but supported by almost 40 years of government research. With the R & D essentially paid for their future their future looks very bright, however they will still be subject to the same funding and management issues of any new company. So far they have these two projects on their books. This will tend to sharpen the the focus of the Pa. based company. Their mission statement does suggest that they will be very interested in SE Asia, Indonesia and even Micronesia.

  • Anonymous

    Good news for Indonesia.

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