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Power Earth Science

Electricity From Salty Water 301

BuzzSkyline writes "It's possible to produce energy by simply mixing fresh and salty water. Although chemists and physicists have long known about the untapped energy available where fresh water rivers pour into salty oceans — it's equivalent to 'each river in the world ending at its mouth in a waterfall 225 meters [739 feet] high' — the technology for exploiting the effect has been lacking. An Italian physicist seems to have solved the problem with the experimental demonstration of a 'salination cell' that creates power given nothing more than input sources of salty and fresh water. The researcher believes that this renewable, environmentally friendly energy source could be deployed in coastal areas and could provide another addition to the green-tech roster. A paper describing the technology is due to be published in an upcoming issue of the journal Physical Review Letters."
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Electricity From Salty Water

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  • Quick! Grab all your salt shakers and run to the bathtub!
  • by 0100010001010011 ( 652467 ) on Friday July 24, 2009 @01:47PM (#28809643)

    he key ingredient in a salt-water capacitor is "activated carbon," extremely porous carbon made from wood, coal, or coconut shells.

    Gilligan could have lived well on that island.

  • by Anonymous Coward

    ...for pissing in a swimming pool?

  • Double Duty? (Score:4, Interesting)

    by drrck ( 959788 ) on Friday July 24, 2009 @01:47PM (#28809657)
    So can we expect this to work in parallel with existing hydro power generation techniques?
    • Re:Double Duty? (Score:5, Informative)

      by localman57 ( 1340533 ) on Friday July 24, 2009 @01:59PM (#28809815)
      Only if the waterfall is on the edge of the ocean...
      • Re: (Score:2, Insightful)

        by AP31R0N ( 723649 )

        Since the Earth is flat (with the Sun orbiting around it), this should be a cinch.

        When we find the edge of the Earth we can push all the Darwinists off!

        • When we find the edge of the Earth we can push all the Darwinists off!

          Should be a cinch to spot from orbit! ... oh wait ...

    • Re: (Score:2, Interesting)

      by mcgrew ( 92797 )

      At first I thought "probably not". Hydroelectric is actually gravity and solar power; you need a waterfall, or a place where the river is channelled into a smaller space (like a dam). Hoover Dam and Tom Sauk come to mind.

      Then I realized that not every river is as big as the Mississippi; Even though most damns are far inland, perhaps you could dam small streams or rivers flowng into the ocean. They dam the big ones bacause the bigger the river, the more power you can get from it.

      What I'd like more explanatio

      • Re: (Score:2, Funny)

        by Anonymous Coward

        in a car analogy please.

      • Re:Double Duty? (Score:5, Interesting)

        by Wrath0fb0b ( 302444 ) on Friday July 24, 2009 @02:43PM (#28810421)

        I got the impression that the writer didn't understand, either. Can any of you chemists/physicists explain this phenomena in layman's terms for us?

        Intuitively, anything that happens spontaneously (e.g. water falling down in a gravitational field) must be downwards in free energy or else it wouldn't happen (with any significant probability). So you know that when you pour together your rum and coke into a glass, the final state (uniform mix) must be lower in free energy than the initial state (rum on the bottom, coke on top).

        Slightly less intuitively, you can understand it very simply with a lattice model of solution under the assumption that there are no energetic effects (true to first order). Imagine the solvent as a lattice in which each square/cube (2D or 3D, your choice) can be occupied by solute or not -- now count up the configurations that correspond to a mixed solution versus an unmixed solution. That difference is configurational entropy and drives it to seek the macroscopic state with the most microscopic realizations since, in the absence of significant energetic effects, every microscopic state is equally likely.

        Of course, it's on wikipedia: []

      • Re:Double Duty? (Score:5, Informative)

        by Tweenk ( 1274968 ) on Friday July 24, 2009 @04:26PM (#28812063)

        In super-layman terms:
        When you put noodles in hot water, they swell. They want to replace noodles with salt water and capture the energy of swelling.

        In slightly less layman terms:
        Recall the principle of induction charging: you hold a grounded metal plate next to a charged one, disconnect the ground, and then remove the charged plate. Both plates are now charged, even though in the beginning one of them was grounded. The effect exploited in the device is similar, except they use the higher concentration ions in the salty water as the 'charged plate' and flushing with less salty water as the equivalent of 'removing the charged plate'.

      • Re:Double Duty? (Score:5, Interesting)

        by James McP ( 3700 ) on Friday July 24, 2009 @04:26PM (#28812065)

        The article actually has an interesting addendum at the end that explains it, albeit in an interesting vernacular.

        In short, salt water is ionic. A small initial electric charge is given to the two pieces of carbon (one positive, the other negative). The sodium and chlorine ions migrate to the respective carbon and thanks to the very high surface area of activated carbon, you get a very high quantity of ions. The water source then switches to fresh water. Elecrostatic force tries to keep the sodium & chlorine ions near the carbon but diffusion pulls them away. The work done to pull the ions away is what generates the power.

        The inventor that it can generate as much as 1.6KJ / Liter of fresh water. If we diverted 10% of the Missisippi River's outflow into one of these facilities you get ~2.6GW of more or less continuous power. (Mississippi = 572,000 ft^3/s * 28.32 L/ft^3 x 10% x 1.6KJ = 2.6GJ/s = 2.6GW)

    • by markk ( 35828 )

      Of course. This has nothing to do with dams or tidal power or anything like that. This is about estuaries and deltas. Think about installations in the Nile, or Amazon deltas. Wherever rivers run into the sea actually. That is where you find fresh and salt water together. It could be a limited but useful augment in some coastal areas. If the fresh water is running into the ocean anyhow we can use "concentration potential" to get some power at the end of the cycle. Ultimately this is solar power which came fr

    • I imagine one day this procedure would be accomplished by desalination plants next to the ocean. Then just pumping in ocean water into the desalinated water. At least one day it could conceivably be profitable enough, especially once we use up our groundwater supplies desalination plants will be in high demand.
      • Re: (Score:3, Interesting)

        by amRadioHed ( 463061 )

        Desalination is extremely expensive, that would be a waste to use a large amount of energy to make fresh water, and then turn around and spoil it to get back a fraction of your original energy.

        On the other hand, desalination plants do create plenty of waste salt, so I wonder if you could get the same effect from the difference in salinity of sea water and the plants extremely salty waste water. You wouldn't make surplus energy, but it could reduce the costs of making fresh water.

      • Re: (Score:3, Insightful)

        by omnichad ( 1198475 )

        The energy taken to desalinate the water is exactly what you gain back by remixing. Could never conceivably be even logical to do that.
        Turning a turbine makes electricity. I know! Let's hook up an electric motor to it to make it spin and generate electricity!
        Oh, oh! And let's start using light bulbs to generate solar power!

  • by Drakkenmensch ( 1255800 ) on Friday July 24, 2009 @01:48PM (#28809675)
    I hope the Energizer Bunny owns water fins and a snorkel!
  • by davegravy ( 1019182 ) on Friday July 24, 2009 @01:55PM (#28809749)

    A device that gleans usable energy from the mixing of salty and fresh waters has been developed by University of Milan-Bicocca physicist Doriano Brogioli. If scaled up, the technology could potentially power coastal homes, though some scientists caution that such an idea might not be realistic.

    Forget scaling it up. Put one such device in every fresh water toilet bowl.

  • Not so new.. (Score:5, Informative)

    by Anonymous Coward on Friday July 24, 2009 @02:01PM (#28809831)

    Actually the technology was already available, and is to be used to power most the majority of homes in the Netherlands, including mine, if the proposal is approved:

    Or the original publication:

  • Too late (Score:4, Funny)

    by BrookHarty ( 9119 ) on Friday July 24, 2009 @02:03PM (#28809857) Homepage Journal

    Too late, Exxon already bought the patent.

  • Clearly, every time I take a leak, I could be generating power from the mixing of my salty urine with clean water during the flush. Also, I should be pissing onto a tiny waterwheel hooked up to an electric generator, and there should be a Francis Turbine on the flush release outflow.

    Next, we'll poop right into a methane extracting farm, and we'll inject pine cones into each person's lungs to extract the exhaled CO2 directly.

    It's perfect!

  • This is actually really interesting! Think about it. We've been limited to solar cells for a long time for producing electricity, and those have limitations we are constantly struggling against. But... Now, you can make a simple isolated enviroment consisting of water and salt. Design it such that fresh water runs down from a resivoir into a lower resivoir with salt. Expose the lower resivoir to sunlight, and use the greenhouse effect to speed up the evaporation of the water. Direct the vapors up to
  • by lazn ( 202878 ) on Friday July 24, 2009 @02:18PM (#28810085)

    "Brogioli maintains that his salinity cell could be ramped up faster than other salination approaches and could be made as affordable as solar power in a decade or so."

    As affordable as Solar in a decade? Solar's main problem now is it's cost!

    • Re: (Score:2, Insightful)

      by jmorris42 ( 1458 ) *

      > As affordable as Solar in a decade?

      Exactly. This is yet another high cost attempt to tap a low energy content source. But then that IS the idea behind 'Green Energy'; to make energy expensive enough to force people to do without. Or more bluntly, to create artificial scarcity for the purpose of reshaping society in ways Greens think wiser than the choices people acting in a free market would make.

      Economic growth, i.e. getting out of this recession (and soon to be depression if we keep digging this h

  • Some ideas (Score:4, Interesting)

    by drinkypoo ( 153816 ) <> on Friday July 24, 2009 @02:19PM (#28810093) Homepage Journal

    One of the best places (potentially) to grow algae for biofuels is in the desert. You could pump seawater inland, and circulate it in pools. If you covered those pools with greenhouses (which could just be big clear balloons... or not-so-big ones, if you use arrays of small pools) and collected water they'd make you some fresh water, which could then be combined with incoming salt water to produce energy to help run the system, whether that would be the pumps, mixing devices which keep the pools circulating, or what ever else have you.

    Another idea for the waste water produced from this process is to pump it inland and use it in the algae pools... so you can have coastal plants whose effluent is used to grow algae for carbon-neutral biofuels, and [optionally] to raise the water table in the desert.

  • Windmills convert wind into electricity. The result...less wind on the far side. That changes climate I'm guessing. Not sure how wind affects things. Hotter animals because of less breeze? Smaller area of seed dispersal? Other things.

    Solar panels take the heat energy out of the sunlight and convert it to electricity. I'd think that would cause the ground to heat up less, but that's probably insignificant compared to the direct change of 'being in the shade' for all the flora and fauna under the sol

    • by smellsofbikes ( 890263 ) on Friday July 24, 2009 @02:59PM (#28810655) Journal
      It's osmotic pressure. You have salty water and pure water, and there's a force produced when they contact, because the ions in the saltier water are driven by entropy into the less-salty water.
      The energy you're stealing is solar power: the sun heats the salty water, evaporating out pure water, that goes up into the clouds and then rains, forming the rivers of pure water.
      This is just a convoluted solar power system. But then again, so is everything else: wind, gravity, and more distantly, nuclear and oil.
      The main environmental issue would be interfering with fish migration, for the many (very economically valuable) fish that live in the sea but spawn in rivers, like salmon. Which, by the way, are near miracles from a biochemistry standpoint, since they live part of their lives in the sea, where they're fighting to keep those same ions out of themselves because sea water has about twice the ion concentration as animal tissue so they have to maintain a more pure internal environment, and then they swim into fresh water, where they have to fight to keep from bleeding all their ions out, since many streams have about 1/2 or less the ion concentration as animal tissue. There aren't that many animals that can manage it.
      • Re: (Score:3, Insightful)

        This is just a convoluted solar power system. But then again, so is everything else: wind, gravity, and more distantly, nuclear and oil.

        The nuclei involved in fission are produced in supernovae. So, I guess you could include that as solar power, but not the way you'd usually think of it.

    • by Yaur ( 1069446 )
      We are talking about a relatively small amount of energy in a very large body of water and we have been undercutting this energy source for a long time. Since it is really solute density that matters not salt density, water pollution is, or should be, reducing how much energy is being released at the interface. From an ecology standpoint the habitat destruction problem is a lot bigger since anything that could do this is likely to significantly drop the salinity of the water in the river mouth and destroy t
    • by jmorris42 ( 1458 ) *

      > Windmills convert wind into electricity. The result...less wind on the far side.

      True, but the amount of energy in the wind is really big and the amount we are likely to ever take out is small. So I'm not too worried.

      > Solar panels take the heat energy out of the sunlight and convert it to electricity. I'd think that would cause the ground to
      > heat up less, but that's probably insignificant compared to the direct change of 'being in the shade' for all the flora and fauna
      > under the solar panel

    • by radtea ( 464814 ) on Friday July 24, 2009 @03:25PM (#28811047)

      Energy on the planet doesn't just SIT there doing nothing.

      Of all the highly concentrated nonsense in your post, this is the highest peak of wrong-headedness.

      Just to take a single example: what is the quantum efficiency of photosynthesis reactions?

      Energy goes to waste all over the place--it would, amongst other things, be impossible to see if it did not! Nature is unbelievably wasteful. The very fact of the existence of oil and coal reserves is testament to this: those beds were all huge amounts of available energy at the time the dead plant matter was deposited. It did indeed "just sit there" on the surface for thousands of years as it accumulated before being buried.

      Energy is "just sitting there" accumulating in peat bogs as I write this, freely available for some magic unicorns or something to come along and use it. I don't see any, do you?

      Finally, your bizarre claim that any change to ocean temperature whatsoever is "enough to disrupt the ecosystem" will stand as a monument to the dangers of innumeracy for generations to come.

  • I read this summary extremely skeptical but after reading the article (which is pretty sparse on detail) it sounds simple enough to work. In principle.

    The problem is this sentence:

    Once he jump starts the cell with electric power, all that is required to produce electricity are sources of fresh and salty water and a pump to keep the water flowing.

    Pumping water is a notoriously is a notoriously energy expensive process. That's why we try to use gravity as much as possible to move our water around. The que

    • Exactly. The thing is supposed to work by diffusion. According to the article, the salt crystals are forced away by the inrush of fresh water, and this movement is what creates the extra voltage. But if your inrush of water is caused by a pump, I don't care how efficient the pump is, you're still not going to produce enough electricity to power the contraption, let alone to get any energy out of it.

      I'm calling this myth BUSTED!

  • Nice to see somebody talking about energy from water salinization once in a while, but that is not the first experiment to gather a few microjoules at lab. Up to now, no aparatus could be scaled up, all of them hit that "we just need better materials" barrier. There is a reason for that, because of the way difusion works, each device can create at most 100mV, and that will fall almost exponentially down to near 10mV once one starts gathering more than 5% of the available energy.

    Just put that on the right perspective, there are just a few specialized diodes that will dissipate less than 100mV on the charge going through it. A normal silicon diode will dissipate 700mV, and there is simply no diode that will dissipate less than 10mV. Also, to get some sane amount of power at 10mV one needs quite a big current, the charge is available to extract that current, but the resistence of your circuit (and the capacitor's dieletric is a piece of the circuit) is a huge barrier. To create 1kW, one'd need a total current of 10^5A (of ions flowing into and out of the coal, if not electrons flowiong throug the circuit), with a total resistence of 10^-7 ohms. To reach such small reistences it is normaly needed lots and lots of material, or "just" better material.

  • Inaccurate story (Score:5, Informative)

    by Otto ( 17870 ) on Friday July 24, 2009 @02:55PM (#28810609) Homepage Journal

    There have been other ways to extract salinization energy: []

    These methods are even being used in test sites to generate power. Main problems are that there's a lot of crap in rivers that you need to filter out to get high efficiencies.

The absent ones are always at fault.