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Saturday, July 01, 2006

Energy from the Sea

28 Years Ago in TR: "Massive ocean thermal energy conversion plants may be turning this heat to usable electricity by 1985." -- William F. Whitmore

By Jessica Baker
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An ocean thermal energy conversion (OTEC) plant. (Courtesy of Lockheed Space and Missile Co., Inc.)

In the October 1978 issue of TR, William F. Whitmore invoked an idea from the 19th century: ocean thermal energy conversion, or OTEC. Exploiting the temperature difference between the sun-heated surface of tropical waters and the chilled depths thousands of feet below, Whitmore argued, could provide clean, renewable energy in the lower latitudes.

In the tropics, the oceans store an immense amount of energy from the sun. The band of surface water within 10º of the equator basks around at 80º F., while cold regions 3,000 ft. below are around 40º F. [OTEC] uses this thermal gradient, like the hot and cold terminals of a gas turbine, to generate electricity. The essence of the system is the circulation of a fluid such as ammonia or propane. Where it comes near the warm water it is brought to a boil and so expands; where it comes near the cold, it liquefies once again. In the course of its circulation from one place to another, it drives a power-generating turbine. A typical closed-loop system would include two exchangers (evaporator and condenser), a turbine, and a generator.

... The engineering challenges to be bridged demand solutions of scale rather than of technical innovation. Ship designs and structures used for offshore oil platforms have blazed the trail for the physical platform on which OTEC will be mounted. A general design goal is to isolate the platform as much as possible from the influence of the ocean surface, where the interaction of wind and wave can induce violent platform motions. A leading candidate is a large spar buoy configuration, with most of the platform mass several hundred feet underwater and a relatively small surfacepiercing mast for access; this would also give warning to marine traffic. The OTEC system, with power cabled to shore, is necessarily fixed in place. Both steel and concrete are considered as possible platform construction materials.

In the 1990s, 250-kilowatt test facilities in Hawaii's tropical waters demonstrated OTEC's feasibility. For a plant to be commercially viable in the United States, however, it would have to produce between 50 and 100 megawatts. Developing such plants would require "patient financing," according to Luis Vega, test director of the largest test plant operated by the Pacific International Center for High Technology Research, which ran the Hawaiian facilities. The first step would be a prototype plant of a few megawatts. Ultimately, Vega believes, not only would a commercial-scale OTEC plant be viable, but it could operate at six to eight cents per kilowatt-hour, making it competitive with other renewable energy sources and even with fossil-fuel plants. But for now, the oceans remain untapped.
July/August 2006

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Comments

  • For the latest on OTEC
    Guest (Thomas Bjelkeman-Pettersson) on 07/11/2006 at 12:00 AM
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    At OTECnews, a non-profit news site, we have the latest developments on OTEC.
    http://www.otecnews.org/
    Rate this comment: 12345
    • potential, yes
      Guest (kitk) on 07/21/2006 at 12:00 AM
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      we have long known this to be a great potential source of energy, and much simpler than say geothermal (and I'm a geologist), and not only renewable but essentially eternal, with the added blessing that most large cities (consumers) are near the sea. now I hate to be a wet blanket, but I bet you if any large-scale plant is built, the sierra club will sue to stop it for fear of creating some temperature imbalance. half the battle to make creative solutions is getting around the obstructors.
      Rate this comment: 12345
      • More than obstruction
        Guest (busted 4xs) on 07/21/2006 at 12:00 AM
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        The Democrat's maniacal political agenda has America running with both arms and legs tied with regards to "Energy Independence" and winning the "War on Terror".  Imagine "Kyoto" bridling what's left of Anerican progress and innovation while allowing other nations to proceed without restraint...which aptly describes the Present.  Our gas tanks generously fund the terrorists and our nations enemies drill for oil near our shores where we are not allowed to drill. Read the Democrat-inspired hate-speak on all the news media discussion sites.  We are canabilized by our own people.  These enegy potentials will never be realized with a Democrat Reformation. Beam me up Scotty!!!
        Rate this comment: 12345
      • imbalance
        Guest (L) on 07/21/2006 at 12:00 AM
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        The thermal imbalance may be positive: if it can reduce the thermal energy stored in the ocean surface a OTEC may contribute to reduce hurricanes violence.
        New Orleans will be saved by OTECs maybe.
        Rate this comment: 12345
        • I missed
          Guest (L) on 07/21/2006 at 12:00 AM
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          ... so if You internalize the hurricanes costs in damages saved OTECs are far more cheap.
          Rate this comment: 12345
        • Exactly what I was thinking...
          Guest (Greg) on 07/21/2006 at 12:00 AM
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          May take some research but several OTEC may create cooler surface temperatures in Hurricane hotspots.
          Rate this comment: 12345
          • In which case, they'd quit working
            Guest (michael) on 07/22/2006 at 12:00 AM
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            When the otec cools the surface, it destroys the temperature gradient it needs to function in the first place.  You run into the same problem in reverse if you pump water into a loop buried in hot rock to heat the water. The ground loop ends up cooling the hot rock faster than the rock can reheat so you end up with no useful heat.
            Rate this comment: 12345
            • True...
              Guest (Greg) on 07/22/2006 at 12:00 AM
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              If you were pumping the heat away fast enough, I don't see having enough OTEC units ceated to actaully to do this. The Ocean is is rather large and with the sun continually heating it, I don't think we could cool it enough to stop it totally, at least for the first century. I'm thinking it would cool the surface just enough to slow or weaken a hurricane.
              Rate this comment: 12345
              • It's a local effect
                Guest (michael) on 07/23/2006 at 12:00 AM
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                The cooling effect need only be local to the OTEC plant to shut down the plant.
                Rate this comment: 12345
                • Local Effect
                  Guest (George) on 07/31/2006 at 12:00 AM
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                  Wouldn't ocean currents negate the local cooling down?
                  Rate this comment: 12345
            • gradient
              Guest (L) on 07/23/2006 at 12:00 AM
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              Incoming solar energy restores the gradient continuosly, this is the reason why ocean's current flow by bilions years.
              Rate this comment: 12345
              • Eventually
                Guest (Michael) on 07/23/2006 at 12:00 AM
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                Yes, solar radiation would restore the gradient eventually as would surface currents. It just takes time which means your power output is limited by that constraint.

                There's another constraint at work here no matter how quickly your gradient is restored and that's the theoretical efficiency. Figure a surface temperature of 90 degrees Farenheit (a probable upper limit) and a subsurface temp of 35 deg F. Convert to Kelvin and you get 305 and 275 respectively. Efficiency is (305-275)/305 gives you an upper bound of 10%. That means your pump losses, friction losses, etc have to come out of that 10% budget. That's cutting it awfully thin - so thin that the pilot plant in Hawaii didn't make more power than it took to run it.
                Rate this comment: 12345
        • Not sure if we would be able...
          Guest (dre) on 07/22/2006 at 12:00 AM
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          To harvest the heat at the scale required to actually cause changes in the weather.
          Rate this comment: 12345
        • imbalance
          Guest (Paul712) on 07/23/2006 at 12:00 AM
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            Water can hold a lot of thermal enery, I forget the formula, and the oceans contain an estimated 100 million-trillion gallons, too much stored energy for the OTEC to have any meaningful affect on hurricanes.
          Rate this comment: 12345
      • Potential Obstructor
        Guest (George) on 07/31/2006 at 12:00 AM
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        It is more likely that the oil industry and the current administration, which is oil oriented, would provide arguments against it.
        Rate this comment: 12345
  • Accountability in Tech Predictions
    Guest (Tom Schaefer) on 07/21/2006 at 12:00 AM
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    I think this article is a good example of why there needs to be accountability and lessons learned from technology predictions.  This article was too short, not discussing the problems with bio-encrustation and the opportunity for aquaculture associated with ocean thermal.
    Rate this comment: 12345
  • Global Warming
    Guest (Vlad) on 07/21/2006 at 12:00 AM
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    If we really are getting hotter as it seems we are, then these power plants which turn that heat into electricity could well be the first step in reversing it.  After all heat energy transformed into electrical energy no longer contributes to global warming.  Personally I dont think we're causing it nor can we stop it if it is happening naturally.  I think global systems are too large for human tinking with but if I am wrong this seems like the best way to cool the planet.
    Rate this comment: 12345
    • Re: Global Warming
      Guest (Chip) on 07/21/2006 at 12:00 AM
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      How do you figure that OTEC electric doesn't contribute to global warming?

      The power produced is used to power electric motors which heat up the environment.
      Rate this comment: 12345
      • Faulty logic, Chip
        Guest (MJ Lincoln) on 07/21/2006 at 12:00 AM
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        1st of all, the electricity generated by the OTEC isn't generated at 100% efficiency, so the heat removed is greater than the electricity generated.  Secondly, electric motors only give off a small portion of their energy as heat.  Most of their energy is expended kinetically.  Also, if you consider the fact that this electricity would be displacing electricity generated from coal or some other CO2 emitting process, then I think it's pretty clear that if this were a viable technology it would have a net-positive impact on global warming.
        Rate this comment: 12345
        • and then you'd be the first the dems would blame
          Guest (pluged up) on 07/21/2006 at 12:00 AM
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          for Global Cooling...;)
          Rate this comment: 12345
          • Zeroth Law
            Guest (Mr. Thermo) on 07/26/2006 at 12:00 AM
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            Guys, read up on the Zeroth Law of Therodynamics.  It all turns back into unconvertable heat energy.  There's no net gain, since the energy originally came from sunshine anyway.
            Rate this comment: 12345
        • Faulty logic Lincoln
          Guest (BrianW) on 07/24/2006 at 12:00 AM
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          heat that is not turned into electricity does not disappear- it is simply transfered to the wrong part of the system (reducing efficiency) or out of the system (into the world.)and how ever the electricity is used, the kinetic energy, ends up as heat in the world (unless you use it to lauch projectiles into space:). However, you are right that in displacing coal, etc, this energy generation theoretically would have an impact on global warming. Of course, that finally depends on whether the development of alternate energy would cause us to use less coal, or just encourage us to use more energy in total.
          Rate this comment: 12345
    • Re: Global Warming
      Guest (perilisk) on 07/22/2006 at 12:00 AM
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      They don't "turn heat into electricity", they just take advantage of the fact that the temperature difference causes movement that can be harnessed for energy. They wouldn't reduce the net amount of heat on the planet, they would just push more of the existing heat into the depths.
      Rate this comment: 12345
      • [no subject]
        Guest (John) on 07/24/2006 at 12:00 AM
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        Not true. If that were true, they would be generating something from nothing, something physics states is impossible.
        Rate this comment: 12345
    • Global Warming
      Guest (Phil) on 07/24/2006 at 12:00 AM
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      It's really not that hard to imagine the greenhouse effect.  CO2 will let the sunshine pass through but then trap in the heat.  We are putting more CO2 into the air then there has been in the history of the planet.  more CO2 = more of a greenhouse effect.  It's just not that complicated and it seems silly to me to deny that it's happening.  Not to be preachy, but start thinking about how you can do your part to reduce emmissions.
      Rate this comment: 12345
    • Thermodynamics 101
      Guest (back 2 school) on 07/25/2006 at 12:00 AM
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      Vlad, and some others, need to take a refresher course in thermodynamics. When you use heat in an engine, you do not make the environment cooler. On the contrary, there will be more heat generated on a total basis...The electricty generated will end up as heat too. So global warming will not be reduced because we will be "extracting/removing" heat from the environment with these maritime convertors. However, this is a clean energy technology, and it has a much smaller environmental foot print. I bet you, a lot of fish will love these floating plants.
      Rate this comment: 12345
  • OTEC Costs
    Guest (Mike) on 07/21/2006 at 12:00 AM
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    Are these things cheaper and safer than a Nuke plant to build and operate?
    Rate this comment: 12345
  • OTEC & EPA
    Guest (Bill Millard) on 07/21/2006 at 12:00 AM
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    Has OTEC been approved by Jean-Michel Cousteau?
    Rate this comment: 12345
  • OTEC didn't work
    Guest (michael) on 07/22/2006 at 12:00 AM
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    Hawaii built a pilot plant on the main island in the 80's. The promised power never materialized but the deep sea water turned out to be perfect for a variety of aquaculture companies. So they didn't get power but they did get abalone. Not a bad consolation prize.
    Rate this comment: 12345
  • Ignorant comments
    Guest (John Bill) on 07/22/2006 at 12:00 AM
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    The comment about the Sierra Club proves how ignorant most people are.     When he made the comment about temperature imbalances, it was said tongue and check [political humor].  Then all these  idiots pile on saying stupid things like maybe this would stop hurricanes or would it heat up the oceans.  You would literally need thousands of monster sized  power plants to even have the slightest effect on the oceans. This is akin to saying using geothermal energy could stop volcano's. And all this time I thought MIT's web site was for intelligent people, who would have guessed.
    Rate this comment: 12345
    • Your comment
      Guest (L) on 07/23/2006 at 12:00 AM
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      My thought about hurricanes is not based on data, I'm ignorant about how many OTECs or how much energy would be need to control thermal flows, but I do not understand how You may dismiss this idea without data.
      Welcome in Ignorant MIT Site Club.
      Rate this comment: 12345
    • on ignorants
      Guest (ignorius) on 07/25/2006 at 12:00 AM
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      Anyone can post on this site, so the users have nothing to do with MIT.
      Rate this comment: 12345
  • 5-year-old update
    Guest (Eric Bender) on 07/24/2006 at 12:00 AM
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    Five years ago I took a quick look at OTEC for Tech Review:

    http://www.technologyreview.com/read_article.aspx?id=12527&ch=biztech
    Rate this comment: 12345
    • I thought many OTECs were plagued by deposits
      Guest (Ben Wiens) on 08/10/2006 at 12:00 AM
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      I remember doing research some years ago on OTEC and read that some shut down because of the constant problem of various sea organisms attaching themselves to the internal and external components and reducing their efficiency?
      Rate this comment: 12345
  • The Ocean Pressure Resource
    oes/opec on 08/22/2006 at 5:41 PM
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    Oceans cover 71 percent of the earth’s surface, and of that total area, 2/3 is deep ocean, 5,000 ft. or more in depth.

    As mankind becomes more aware of the environment and the present increasing consumption of energy and the ultimate limitations of conventional power sources, the oceans are being studied more closely in an attempt to find long-range solutions to the energy and environmental problems.  In that regard, man has investigated numerous systems designed to make use of the oceans as an active source of energy.  As a primary resource the ocean contains a number of sizable potentials for power production.  Potentials for mechanical, thermal, organic and nuclear power exists in a number of different forms.  Various reservoirs of extractable energy are present in the oceans, for example: heat, thorium fission, uranium fission, deuterium fusion and hydrogen fusion.  The use of these energy resources, apart from ocean thermal energy, would be equivalent to mining the resource as the raw materials and would not be renewed to any substantial extent.  Renewable energy sources consist of ocean currents, tides, waves, salinity gradients and thermal gradients.  Of these, only two, salinity gradients and thermal gradients, are of an order of magnitude that would supply a large part  of the vast eventual human needs.  Fairly conventional machines have been prototyped in an effort to tap the renewable energy sources that the ocean has to offer except in the case of salinity gradients.

    There is however, another renewable, non-depleting energy source of a similar magnitude which the ocean offers, but has been overlooked.  This renewable, non-depleting energy source is the ocean’s pressure gradient.  This pressure gradient increases with depth at a rate of approximately .46 psi per foot of depth.  At an ocean bottom depth of 5,000 ft., a pressure equal to approximately 2,300 psia can be found.  If it were possible to utilize this high pressure relative to atmospheric pressure at sea level of 14.7 psia, then a very significant, renewable, non-depleting energy resource could be had for the production of power.

    We are in the process of developing an ocean pressure energy conversion (OPEC) power generation system, which uses the pressure difference, (?P), between the pressure of air at sea level and the pressure of the ocean water at the depth of its bottom to compress air to a high pressure.  The high-pressure air then serves as an easily used energy source, which could be utilized to power an expander producing rotational energy converted to electrical power by a generator.  The exhaust from the expander is pure air - no pollution and no effect on the environment; and the electrical power produced is from a renewable, non-depleting energy resource.  The end uses of the electrical power generated by the OPEC System would be furnishing electrical power to the grid, the production of fresh water from seawater through desalinization and the production of hydrogen from seawater through electrolysis.  Contact information:  rlagow@alltel.net
    Rate this comment: 12345
    • Re: The Ocean Pressure Resource
      frankie on 10/05/2006 at 3:31 PM
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      Your idea is not a new idea.  This is something that I have doing research on FOR YEARS.    

      It is DEFINITELY not as simple or as you state on your post. If you think that it is as simple as you state, then you have a whole LOT of research to do.
      Rate this comment: 12345
      • Re: The Ocean Pressure Resource
        Roy on 05/01/2007 at 1:58 AM
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        Avg Rating:
        4/5
        Could someone enlighten me as to how the pressure gradient migth be used to generate power? If the gradient is caused by gravity then it seems that you can' get any net work out over a full cycle.
        Rate this comment: 12345
    • Re: The Ocean Pressure Resource
      newenergyman on 04/17/2008 at 9:24 PM
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      This is very interesting. I have also developed an OPEC (Ocean Pressure Electrical Conversion) technology; and have been working with it since 2003. I had a website concerning it in early 2006 to 2007 (www.hydropshereonline.com), which is now defunct.

      Interestingly, I emailed many university professors, across the U.S. including some at MIT, professors concerning my invention and device in 2005 and early 2006. Perhaps they took the idea and ran with it, so to speak?

      In any case, you can read about the latest evolution of my OPEC concept and AWG (air-water-gravity) generator, which works off differentials between pressure at depth (hydrostatic pressure) and normal atmospheric air pressure inside the device, which is submerged on sea or lake bed. You can see a discussion on www.beyondfossilfuel.com and PES WIKI.

      I guess this is the risk anytime you publicize a new technology; but the more people looking at it and refining it, the better for the world.
      Rate this comment: 12345
  • wind energy
    anergia323 on 09/01/2006 at 4:49 PM
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    1
    birds and wind mill do not mix very well,i got an idea how to solve the prblema
    Rate this comment: 12345
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