Seawater electricity

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

  1. CDK
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    CDK retired engineer

    One very good reason why doing that would be 100% senseless:

    Batteries are stacked to obtain a usable output voltage, like 3 cells in a flashlight, 6 cells in a 12 V car battery. To achieve that, individual cells are connected + to -. Dissimilar metals dangling in the sea have a common electrolyte, hence the voltage is limited to that of a single cell.
     
  2. capt vimes
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    capt vimes Senior Member

    you are right... in theory... ;)
    the energy which goes in - comes out... but you are not able to convert this energy to a 100%....
    you will have losses when splitting the water... resistance, thermal losses and such which will force you to but more energy than needed to it...
    and you will have losses when you burn H2 to water again... giving you less _consumeable_ energy back than there actually is generated... far less by the way... ;)
    remember - a combustion, piston engine works with not even 35% of efficency... ;)
     
  3. Dave Gudeman
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    Dave Gudeman Senior Member

    True. Neither the energy that you put in to get hydrogen nor the energy that you get out from the hydrogen would be 100% efficient. You would have losses on both ends.
     
  4. Boston

    Boston Previous Member

    ok so Im a little rusty on all this but two dissimilar metals in an electrolyte produce a charge

    electrolyte being a abundance of free hydrogen

    ends up producing oxides
    ok

    so why do they use lead oxide paste over a grid to produce the modern lead acid battery

    now Im confused

    B
     
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A lead acid battery has different chemistry. When discharged, all plates are covered with PbSO4 and the H2SO4 acid has weakened. Charging returns the SO4 to the acid and changes the plates into Pb (+) and PbO2 (-).

    Starting with pure lead plates and charging was the old way to make batteries, using PbO2 produces so-called dry charged cells, saving a lot of time.
     
  6. Boston

    Boston Previous Member

    hmmmm

    so in essence you could burn lithium and aluminum instead of fuel and buy lithium instead of diesel

    hmmmmm
    I wonder how that works out in terms of $ per mile
     
  7. capt vimes
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    capt vimes Senior Member

    you are definetely not "burning" (wasting) lithium!
    this stuff is so sparse on this farking planet that nobody wants to just burn it off...
    i do not understand duracell i.e. bringing some one-way, unrechargeable lithium batteries to the market when one could produce high power rechargeables with lithium...
    hell - i never understood economy... it just makes no sense if you think about it....

    why is lithium so good?
    it has the lowest electronegativity of all known elements and - as CDK has already pointed out - the voltage you get from any electrical source where you simply connect 2 different conductors is based on the materials electronegativity... there is no better stuff known than lithium...

    you do not wanna burn that and dump it in a bin!
     
  8. Boston

    Boston Previous Member

    sooooo
    how would you go about recovering the lithium once the reaction has taken place and wouldnt that end up taking more energy than it gave up ( yes )
    basically how expensive is lithium and is it worth it to either manufacture an artificial alternative or produce a non rechargeable battery

    just kicking around some ideas

    B
     
  9. mcollins07
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    mcollins07 Senior Member

    The U.S. government has been funding the development of fuel cells for many years. These are a type of battery where the plates are a catalyst, the liquid is something like alcohol. The alcohol reacts with the catalyst producing electricity as a battery would, but instead of recharging it, you add more fuel. I do not know the state of the art on this, perhaps someone else does?
     
  10. capt vimes
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    capt vimes Senior Member

    there are various types of fuel cells...
    http://en.wikipedia.org/wiki/Fuel_cell

    what they have all in common:
    low efficency and low voltage... (0.6-0.7 V for 50% efficency)
    and than there is this nasty behaviour: the stronger the current you draw from the cell, the lower the voltage you get and decreasing efficency even further...
     
  11. Dave Gudeman
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    Dave Gudeman Senior Member

    Warning: the following is all guesswork.

    You could probably burn lithium in a boiler to run a steam engine. I guess you could melt it and run it through an internal combustion engine of some sort, but I doubt it would be much like current IC engines since I doubt the burning properties of liquid lithium are similar to the burning properties of hydrocarbons and alcohols. Also, the main byproduct of burning lithium is lithium oxide which melts at 2858 degrees F so I doubt very much of it would go away in the exhaust. You would have to find some way to flush it out of the system (hint for researchers: :) it does dissolve very rapidly in water).

    I assume you could recover lithium from the lithium oxide by some process, but I don't know how.

    However, if you want to use lithium as a fuel, I would guess that you could do it more efficiently by going electric and using the lithium in a lithium-air fuel cell than by actually burning it.

    By the way, lithium is not at all a rare element and it is used in lots of other applications besides batteries.
     
  12. Boston

    Boston Previous Member

    I was using the term figuratively

    someone had said that the reaction results in the loss of metal

    by burning lithium what I meant was using it up in the fuel cell

    so if lithium is cheap then why not just build a number of cells in series and provide for replacing the aluminum and lithium from time to time

    or would that end up substantially heavier than typical batteries
     
  13. Dave Gudeman
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    Dave Gudeman Senior Member

    No, it would be substantially lighter than typical batteries for the same energy storage. The main problem is that currently you can't recharge lithium air batteries, you have to recycle them.

    Also, they might be more expensive. I don't know if commercial ones are available or how much they would cost. Lithium is cheap, but so is hydrogen, and hydrogen fuel cells are expensive because they need a very expensive catalyst (usually platinum).

    Still, I expect that the next big jump in battery energy density will come from metal air fuel cells. Or, to be more precise, you can already get metal air fuel cells that have much better energy density than normal types of cell, but they have various disadvantages to overcome before they can replace batteries in certain applications like running laptop computers and boats.
     

  14. Boston

    Boston Previous Member

    could you use a solar cell to run the thing backwards and electroplate the metals back into position on the plates

    sorta a passive recharging system
     
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