Seawater electricity

Discussion in 'All Things Boats & Boating' started by Paul No Boat, Feb 15, 2010.

  1. Paul No Boat
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    Paul No Boat Junior Member

    Maybe this is dumb but I gotta ask anyway. I am seeing a lot of discussion about solar panels etc. and that certainly has a lot of merit in today's climate of green curiousity.

    What was the experiment we all did as kids where you salted a grapefruit and powered a grain of wheat bulb from the resulting electricity?

    Makes me wonder what could be extracted from saltwater using some kind of citrus based paint or some other such medium that would react with the water flowing past a boat. I know it would be miniscule, but so is the current from a solar panel. True trickle charging. Is this possible?
     
  2. mcollins07
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    mcollins07 Senior Member

    Paul,
    the salted grapefruit experiment that I'm familiar with puts an iron nail and a piece of copper in the grapefruit. the grapefruit provides salt bridge as well as citric acid. There is a chemical reaction on the metals which creates the difference in potential. You could do a similar thing by putting iron and copper rods in vinegar, or iron and zinc. We typically use these principals to create an electric potential on boats by putting an zinc anode which is electrically attached to the other metal parts of the boat such as engine, prop, and shaft. The zinc does disolve in the saltwater, and puts a very low potential on the other metals which helps prevent them from disolving. So, there is a basis for you idea, but as far as I know, no one has tired to use this concept to produce enough electricity to charge a battery. I see problesm getting the desired voltage. I think it would be rather expensive, in the cost of the zinc. Also, if you scale up the size of your zinc electrodes, I have heard of problems in scaling up this setup on a boat. The stories are not consitent enough to know the exact problem, but I would not be surprised to find some problems.

    ~ Michael
     
  3. Paul No Boat
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    Paul No Boat Junior Member

    I have seen the anti corrosive technologies you speak of but there we are talking millivolts. Not usable power.

    my idea would most likely be like a Sterling Engine capable of powering it's own existance but otherwise nothing more than a curiousity.

    I'm just one of those abstract thinkers always looking for the uncommon in the common. Someday I might find it. LOL

    thanks for your reply.
     
  4. mark775

    mark775 Guest

    Paul, a few years ago I was researching lighter batteries for a project (that failed!) and came across, I believe, a Finnish company with forward-looking statements about aluminum/air batteries. It got me thinking, "why not with seawater the electrolyte?" It doesn't have to be zinc, aluminum is almost as noble, magnesium, more. It's that aluminum is (was) cheap here. Got busy on other things but keep us informed - it intrigues me, too.
     
  5. CDK
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    CDK retired engineer

    In any battery the anode and cathode produce electricity, not the electrolyte. Your car battery doesn't die from the sulfuric acid weakening, but because the plates develop holes or short circuits.
    Two plates of different metals in seawater make a battery, the size determines the current, the choice of materials the voltage. Metals producing a high voltage are zinc (+0.7V), aluminium (+1.6V) , lithium (+3.0V), silver (-0.8V) and gold (-1.5V).

    So a plate of gold and one of lithium in the water make a 4.5V battery to power your cell phone until the lithium is dissolved or the gold stolen.

    Btw, currents from a solar panel aren't miniscule, there are single cells delivering 2.5 amps. I was able to weld sheet metal with 2 sq. meters of solar panels.
     
  6. thudpucker
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    thudpucker Senior Member

    You guys are going to Ionize the ocean and turn yourselves into a piller of Salt :)

    Can you imagine the Electrical Fields in and around a warship that went down in the ocean during WWII?
    All that Brass, Copper, Aluminum etc immersed in Salt water.
     
  7. gonzo
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    gonzo Senior Member

    Get rid of the anodes and connect your electrics to dissimilar metals in your boat. That was tongue in cheek, but based on real facts. Voltaic cells are based on one metal eroding. It would take a new anode to keep your electrics going.
     
  8. mcollins07
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    mcollins07 Senior Member

    How about Cold Fussion?

    Cold Fussion is a method of generating electricity from sea water. A lot more complex, but the D20 which is the source of energy is obtained from the sea. There is an initial high cost of Pd, and initial input of electricty to saturate the Pd with deturium, but then one should obtain a sustainable source of electricity which might supply the recovery of D20 from the sea water. Sea water would be the ultimate source of the electricity.
     
  9. Dave Gudeman
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    Dave Gudeman Senior Member

    As CDK said, the electrolyte (that is, the salt water) doesn't supply the energy. The water is just there to make the reaction happen. The metals themselves are the actual "fuel" in the battery. Since you get no energy from the sea water, you might as well use a nice clean isolated electrolyte instead of the ocean, and then you end up with a metal-air fuel cell.

    Google for "aluminum air battery" and "zinc air battery". These are really fuel cells rather than traditional batteries (electrochemical cells). Metal-air fuel cells oxidize a metal with oxygen from the atmosphere instead of relying on a purely internal chemical reaction. This gives them much higher energy density than traditional batteries.
     
  10. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

  11. Paul No Boat
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    Paul No Boat Junior Member

    Interesting read, Hoytedow.

    Forgive me, gentlemen. I am digesting this at the level of a 6th grade science student. But since I started this thread I feel I should stay in it.

    From what I read it is not a matter of whether it could work but of the economies of scale involved. Could a boats hull or at least the keel be made into a battery by sheathing it with dissimilar metels or paints based on disimilar metals (copper paint stipes between aluminum paint stripes) and then produce usable current to charge a battery while sitting in water? and how long would the metal plates last before deteriorating to a non usable surface? I know there are a million by products to this. I just want to know if it would work.
     
  12. Fanie
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    Fanie Fanie

    Hi Paul, using the correct materials yes it could work, BUT it will have low voltage, corode your parts away and cause some polution. Not a very usable setup.

    You prbably have a better chance to generate some hydrogen from the sea water and use that as a fuel to generate power and more hydrogen. A tricky setup, but possible. Won't see the commercial market untill they found out how to charge the crap out of you for a liter of sea water...
     
  13. Dave Gudeman
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    Dave Gudeman Senior Member

    Yes, ignoring the "by products", it would work.

    I'm not sure you understand that one of the "by products" is that your boat will be destroyed by turning the hull into into a metal oxide. We didn't answer the question directly since this minor side effect seems to render the idea impractical. :)
     
  14. Dave Gudeman
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    Dave Gudeman Senior Member

    Fanie, that is not possible. Burning hydrogen produces water. It produces exactly the same amount of water that you originally disassociated to get the hydrogen and it produces exactly the same energy that was used to disassociate the hydrogen. The reaction works like this:

    2 H2O --(E)--> 2 H2 + O2

    2 H2 + O2 --(-E)--> 2 H2O

    The number in parentheses represents the energy put into the system. When you disassociate water into hydrogen and oxygen, you have to put energy E into the system to break the chemical bonds. The energy depends only on the bonds and does not depend at all on what process you use to break the bonds. You can't weaken the bonds without putting in a proportional amount of energy. You can't just make the bonds go away. The molecule is in a low-energy state and in order to put it in a higher-energy state you have to supply the energy. When you burn H2 in O2 to get water, it releases exactly the same energy back.

    This is a classic closed system and if you could make it work then you would be violating the principle of conservation of energy.
     

  15. Paul No Boat
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    Paul No Boat Junior Member

    Dave, I do understand there would be a lifespan to this system. Was just curious as to whether it could even work. Many alternative energy sources are short lived toys at best. for now but interesting to say the least.
     
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