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Home Forums Archive Infrastructure OTEC

This topic contains 25 replies, has 14 voices, and was last updated by Profile photo of CrosiarCM CrosiarCM 7 years ago.

Viewing 15 posts - 1 through 15 (of 26 total)
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    Profile photo of Hermit

    For a sea based system, it seems to me (in my rather limited experience) that OTEC would be a perfect system to provide power.

    OTEC stands for Ocean Thermal Energy Conversion. The basic idea is that you use the temperature difference between warm surface water and cold deep water to power a heat engine to generate power. Because the temperature difference between these two heat reservoirs is small, the efficiency tends to be quite low. The technology required is not at all unlike the technology in your refrigerator. Furthermore, the lower temperatures make it easier to design than traditional heat engines that operate at much higher temperatures.


    Profile photo of Sundiver

    I would agree Hermit. Sea Solar Power is ready to build one. (www.seasolarpower.com). Now. You are correct that the efficiency is low, but I’d add that that is irrelevant. Combining it with wind, wave and current power is also feasable on a large platform. Essentially unlimited fresh water is a by product. H2 would be a primary product. JTEC is a new technology that could also be incorporated. Open ocean aquaculture and seafood processing are also compatible (using deep (cold) ocean water to aid flash freezing).

    The seastead needs a raison d’etre to ever become reality. My entirely unsolicited opinion is that Seastead needs to focus on becoming a business with viable products. The USA, for instance is just not repressive enough to inspire competent people to choose anarchy over prosperity. Anarchy or freedom is a fine ancilliary goal, but without an economically based focus, it’s just a hobby.

    “Prosperity is only an instrument to be used, not a deity to be worshiped.”

    Profile photo of

    We talk about OTEC in the book, very briefly. OTEC is big and expensive, so it will be quite a while before it makes economic sense. As the communities get bigger, OTEC will become more and more attractive.

    Profile photo of Sundiver

    Solar assisted OTEC-

    Thought it up and googled it. The energy island guys aready though of it in a different form.

    OTEC operates on a temperature differential of about 40 deg F between the cold deep water and warm surface water. Increasing the temperature difference increases the output or reduces the size/cost of the plant. Using a floating breakwater of the dissipation type (seawalls are impractical in the open ocean) as a solar preheater increases the effeciency of OTEC.

    Profile photo of Joep


    There is a page on the wiki http://wiki.seasteading.org/index.php/OTEC. OTEC keeps popping up in different threads and blogs, I’d suggest we collect everything on a single page instead of restarting the same discussion over and over again.


    Profile photo of MattM

    OTEC is one of those perennial favorites of ocean-based community projects, but it has huge problems that rarely recieve the attention they deserve.

    1. It is very imature technology. Someone is going to need to drop a huge pile of loot into R&D to get to full scale, production ready hardware. (Think 100’s of millions of dollars)

    2. OTEC requires very warm surface water to be efficient, which limits seastead location. (equatorial ocean only)

    3. OTEC requires very deep water to be efficient, which limits seastead location. (Usually WAY offshore)

    4. Efficiency increases with size, so good OTECs are very large and don’t scale down easily. You need a large seastead to make it worthwhile.

    5. Fresh water is a byproduct of the more technically challenging open cycle design. The more near term closed cycle OTEC does not produce fresh water directly.

    6. Very few sites are suitable for land-based OTECs, which means if you drop the $$$ to develop one, there is not much of an export market.

    My opinion: for near term off the shelf power go with diesel fuel generators for baseload power supplemented by as much wind and solar as you are willing to waste your $$ on. (Diesel will always cost less than the renewables once you factor in $300/sq ft for top deck space and huge costs for battery storage) If you have megabucks and want to develop a new power souce from scratch, design a gas turbine based nuclear particle bed reactor. They work 24 hrs per day everywhere on earth, scale down well, and would be a hot export item.

    Profile photo of vincecate

    >(Diesel will always cost less than the renewables once you factor in $300/sq ft for top deck space and huge costs for battery storage)

    Always is a long time. You can mount the solar as a sun shade above your top deck so it does not really take up valuable space. And some designs like http://www.floatingislands.com/wavebreak/ are probably way under $300/sq-ft anyway. If you factor in a few other things solar is very interesting.

    1. solar panels can last 30 years and diesel generators don’t
    2. solar panels don’t need maintenance and diesel generators do
    3. diesel generators are noisy and smelly
    4. diesel fuel will probably be going up in price over the next 30 years, once you paid for your solar you are done
    5. diesel delivered to a seastead in the middle of the ocean is probably going to be more expensive
    6. several credible companies say they will soon produce solar panels at a fraction of the current price
    7. in the deep ocean we could store energy using a weight and a couple miles of rope and not need batteries – http://wiki.seasteading.org/index.php/Energy_Storage

    I think solar is already reasonable on islands and by the time we are really moving onto seasteads it will be the way to go.

    Profile photo of thebastidge
    • Actually, diesel generators can last quite a long time.
    • Electrical generation doesn’t develop the same torque as moving things up and down big hills. I believe that ship engines also last longer than land-based engines- they never have quite the same level of torque applied to them.
    • Diesel engines have a longer designed lifespan than gasoline engines anyway, and with proper maintenance probably will last 30 years.
    • Solar panel do need maintenance. They must be cleaned, and connections may not weather well in marine environments. They also slowly lose efficiency over their lifespan.
    • Diesel generators are noisy. Biodiesel gets rid of some of the smell
    • Diesel will probably go up in price, yes.
    • Diesel delivered to the middle of the ocean is undoubtedly going to be more expensive thaqn diesel on land.
    • Several credible companies are always making claims that they will soon produce cars that go 50 mpg without sacrificing any comfort or ability.
    • The gravity battery idea has yet to be proven
    Profile photo of
    • Difference in ship vs land diesel durability – seems unfounded to me. Depends on the application – a car diesel that will be shifting RPM and starts and stops all the time will probably be subject to higher wear than a generator that is always on and always at the same RPM. In the end all engines will last for as long as they are designed to last. I think diesels used to be more “overbuilt” than gasoline due to the higher compression etc but I don´t think that is the case today, with car engines anyway. After all, if the engine lasts way longer than the rest of the car the manufacturer is wasting money.
    • Diesel engines are way cheaper than PV cells of the same output. I´m guessing that the engine cost is negligible next to the fuel cost in the long run – with the total operating cost for diesel still being much less than solar cells..
    • Most diesel gensets are probably made for emergency power. We will obviously need stuff that is built for around-the-clock all-year-round operation. This might be more expensive. Or use cheaper emergency generators but keep more spare units.
    • Sorry about the off topic post. I´m sure OTEC will be possible, and perhaps economical, in the future.
    Profile photo of

    Storing energy with gravity is going to be very wasteful since water has huge drag forces acting on the weight. The alternative to this form of storage is to build an airtight tube for the weight to move along but that will probably have big safety concerns. I’m not an expert. There’s still the friction of the rope even if the tube is airtight. I have no idea how efficient gravity storage is.

    Profile photo of vincecate

    The pressure a mile down is huge. A pipe big enough to hold a significant weight and strong enough to hold back the water would be very very expensive. Then you can still have friction of the weight/rope against the inside of the pipe. Don’t think that is practical at all.

    But the weight on a rope idea may not be as bad as you think.

    Make a long skinny weight by filling a metal pipe with lead. The weight is on the order of 10,000 lbs. The energy of dropping the weight 3 miles should last a family for more than 24 hours, so the speed is like 0.1 MPH. The shape of the weight slides through the water easy and the speed is very low. Power loss to drag like this goes up with the cube. For such low speeds it is not much. Out of the 10,000 lbs force, I think you are losing well under 1 lbs, or 1/10000th of your energy to drag. Look at me pulling this 32 foot long, 1 foot wide, and 3 inches thick, thing made of 8 sections through the water at like 2 MPH with my pinky finger and maybe 3 lbs of force:


    Anyway, I think the drag loss from the weight should be acceptable.

    The cable would have to be kept clean of sealife. Down in the deep ocean you don’t have light so not so much grows. The shape of the cable should be low drag. Maybe a plastic coating on the outside. I think the drag on the long cable is more of an issue but probably ok.

    But yes, the total efficiency of this needs to be evaluated. But any energy storage system will have some loss.

    Profile photo of ninjasmoke

    Anyone, thinking diesel is the way to make electricity need to have real experience with its cost and maintenance! To date on the island of Saipan which is part of the USA for those of you who don’t know that is costing $0.38 kw/hr. It is breaking the economy there! Possible OTEC sites are many but no one seems to want to get off their butts and invest! They are waiting for big government to do it. Well, at that rate it will be another 30 years if at all.

    Diesel, is only a temp. and as oil cost rise as they are now and will even more as China gets into importing more as it already has the price is going to be to high for island nations to afford it. Yes, even Hawaii!!

    Profile photo of ninjasmoke

    OTEC is very practical and it can be done NOW!

    A mist lift OTEC plant can be up and running in no less than 6 years. It does not need to be HUGE either (1 to 5 mega watt).

    Yes the deep water pipe will be expensive but will within reason. And yes it would work best in the tropical waters.

    A 5 megawatt plant could be built for $50,000,000.00 or less and yes it is marketable. Once one is built many nations will be knocking at your door for one or ten or hundreds. It is just a concrete vessel with simple design and once running if won’t need hot or cold water pumps. It is capable of lifting water to the height of Nigeria Falls and dropped down into a conventional hydro generator. The Man who came up with this concept is still alive.

    Anyone interested??

    Profile photo of vincecate

    In Anguilla the electric company uses diesel and the cost of electricity here is $0.45 US per kwh. I aircondition a well insulated dome and my electric bill is about $2,000 US per month. I was very happy this week when I found out there are now airconditioners that are about twice as efficient as the one I am currently using (currently 5 tons at 10 SEER and going to 5 tons at 21 SEER – Carrier Infinity series).

    In the US government subsidies covering about half the cost of solar power make it competative with $0.11 per Kwh electricity. But since our rates are about 4 times the US rates, we don’t need any subsidy to make solar win out. So I fully expect to put in solar sometime in the next few years.

    I think solar prices are going to drop enough over the next year or two that I am not in a big rush to buy stuff now.

    Anyway, I think diesel is not going to be the way to go for seasteads. I think solar will be.

    Profile photo of

    We will use whatever is the most economical. Diesel is 24×7. Solar requires batteries and power conditioning to get to 24×7. I’d willing to pay a modest premium for solar over diesel if it means that we do not have to steadily import diesel fuel. I expect we will have a mix of power sources — solar, wind, wave, and diesel. I am hoping that diesel is the backup power source, rather than the primary.

    With regards to OTEC, $50M is way be beyond our budget at this point in time.

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