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Electricity From Salty Water
Posted by
kdawson
on Fri Jul 24, 2009 12:43 PM
from the foaming-brine dept.
from the foaming-brine dept.
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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Quick! Grab all your salt shakers and run to the b (Score:5, Funny)
If only the professor knew. (Score:5, Funny)
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.
Re:If only the professor knew. (Score:4, Funny)
Parent
Double Duty? (Score:4, Interesting)
Re:Double Duty? (Score:5, Informative)
Parent
Re:Double Duty? (Score:5, Interesting)
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: http://en.wikipedia.org/wiki/Entropy_of_mixing [wikipedia.org]
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Re:Double Duty? (Score:5, Funny)
I donmt understanf i poored five rum nf cokes and this made les ssens each time
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Re:Double Duty? (Score:5, Funny)
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Re:Double Duty? (Score:5, Informative)
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'.
Parent
Re:Double Duty? (Score:5, Interesting)
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)
Parent
Re: (Score:3, Interesting)
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)
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!
Re:Double Duty? (Score:4, Interesting)
Desalination plants produce brine, though, which has more salt than ocean water, so conceivably you could increase the efficiency by combining seawater and brine.
Parent
The water battery: now a reality! (Score:4, Funny)
Urine Powered Society (Score:5, Funny)
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)
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:
http://ecoworldly.com/2009/03/08/saltwater-power-could-supply-energy-for-most-dutch-homes/
Or the original publication:
http://pubs.acs.org/doi/full/10.1021/es9004224?cookieSet=1
Too late (Score:4, Funny)
Too late, Exxon already bought the patent.
FTA: the real problem (Score:5, Insightful)
"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!
Some ideas (Score:4, Interesting)
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.
Of course with better materials it'll get better (Score:3, Informative)
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)
There have been other ways to extract salinization energy: http://en.wikipedia.org/wiki/Reverse_electrodialysis [wikipedia.org]
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.
Re:neat (Score:4, Informative)
Keep in mind desalination is
salt_water -> salt + water
whereas this reaction is
water + salt_water -> less_salty_water
You'll note that they're not exactly inverses of each other.
Parent
Re: (Score:3, Informative)
Keep in mind desalination is
salt_water -> salt + water
Show me a single commercial example where this is the case.
Desalination is:
lots of salt_water -> lots of slightly_saliter_water + a little fresh_water
High rejection ratios help reduce the energy requirements as greater temperatures or pressures (depending on the method) are required for greater salt concentrations.
Re:neat (Score:5, Insightful)
Parent
Re:neat (Score:5, Funny)
This would be a great way to power all those desalinization plants on the coast!
Parent
Economy is a Subset of Ecology (Score:5, Insightful)
Don't bother. PETA and Greenpeace both called and said it'll kill too many endagered fish species.
While PETA and Greenpeace may have different definitions of "too many" than you do, balancing concern about impacts on fish stocks with concerns about energy is a perfectly reasonable thing to do, given that fish are part of our food supply (and food chain).
There's also issues like whether or not a given fresh water supply might have better uses.
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Re:Economy is a Subset of Ecology (Score:5, Funny)
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Re:Economy is a Subset of Ecology (Score:5, Funny)
I thought our food chain was Sun -> Corn -> Cows/Pigs/Chickens -> Cows/Pigs/Chickens -> Dinner.
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Re:Economy is a Subset of Ecology (Score:5, Funny)
I thought our food chain was Sun -> Corn -> Cows/Pigs/Chickens -> Cows/Pigs/Chickens -> Dinner.
We have a backup system:
??? -> Taco Bell -> Dinner.
Parent
Re:Economy is a Subset of Ecology (Score:5, Funny)
And Taco bell is environmentally friendly as they use non-organic material to construct their food out of.
Parent
Re:Economy is a Subset of Ecology (Score:4, Funny)
Thanks for pointing out my lack of grammar Mr. Commissar.
It is much being appreciated by me.
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Re:Economy is a Subset of Ecology (Score:4, Insightful)
Lets not paint greenpeace or peta as reasonable organizations. PETA is just a joke and I blame Greenpeace for the lack of nuclear power plants, thus the burning of all this coal. Its like the anti-abortion crowd's disapproval of condoms and the pill.
Neither of these groups express proper concern for anything. They are well-off non-profits riding the donation train. Being shrill and unreasonable equals donations from the nutters of the world.
Parent
Re:Economy is a Subset of Ecology (Score:4, Interesting)
Somewhat inaccurate. They have offered a reward to the first person to make in-vitro meat, where the meat is grown independent of the animal, economically viable. They oppose "unethical treatment," which is defined broadly enough to mean killing or confining an animal for virtually any reason. Bruce Friedrich, a spokesman for PETA, has said that if in-vitro meat were available, he'd eat it in a heartbeat. After all, no animal would have to suffer to provide it. It's a consistent position, which I respect.
Before anyone starts, I'm aware of hypocrisy in other areas (PETA pet shelters), but I'm addressing only their views on vegetarianism.
Parent
Re: (Score:3, Funny)
Indeed, the free market will sort it out. Like for instance, dodo eggs got really expensive, so the price went up, fewer people bought dodo eggs, so the price went down... um... hang on.
Re: (Score:3, Insightful)
No, what happens is the price goes up and that makes the fish an even more attractive target to fisherman. This is an example of the tragedy of the commons, a failure of the free market.
Re:What about the fishies? (Score:5, Funny)
PETA and Greenpeace both called and said it'll kill too many endagered fish species.
Dang it! I warned these people. Last month I sent them a letter:
Dear PETA,
While I love animals as much as the next guy, I'm sick and tired of your stupid press releases. You do more harm than good by making animal lovers seem rediculous to the general public.
Therefore, I have no choice but to make you reconsider your PR tactics. Starting next week, any time you issue a press release that does animals more harm than good, I'm going to the pet store, and buying a hampster. Then I'm going to take it out in the parking lot and hit it with a shovel.
Sincerely,
LocalMan57
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Re:What about the fishies? (Score:5, Informative)
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Re:What about the fishies? (Score:4, Funny)
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Re:What about the fishies? (Score:5, Insightful)
Don't bother. PETA and Greenpeace both called and said it'll kill too many endagered fish species.
Fish? Oh, you mean sea kittens [peta.org].
Parent
Re:Brilliant, Holmes, brilliant! (Score:4, Insightful)
There are serious transportation issues with piping potable water from places where it is plentiful to places where it is needed. That's WHY we have a potable water crisis in some areas (especially the American Southwest) while we have no problem whatsoever in others (like the Northeast or the mouth of the Missisippi). In those places there's already huge amounts of water flowing into the ocean. This technology would allow that water that is already being mixed with ocean water to generate electricity in the process.
Also there are situations where water is not potable due to issues other than salinity, and for the purposes of this process might be considered "fresh" compared to saline water.
An interesting thing would be if this could be used to provide for cheap solar power - Some of the largest "solar power" we use today are salt concentration ponds - they don't provide electrical power BUT they do provide the function of separating salt from water in large solar ponds. It would be horrendously inefficient per unit of surface area, but the cost is so low that large surface areas could be achieved.
Parent
Re: (Score:3, Insightful)
If you RTFA (pardon me, I forgot this is SlashDot) the same effect can be gotten by mixing salt water with more highly salinated water (made by evaporating sea water - say, using a solar evaporation pool) or lightly polluted water (non-potable).
I could also venture a guess, based on the fact this is a solution postulated for coastal locations, that the process could also be sited at or near the mouth of a river - say one the empties into the sea or ocean? In that case only fresh water that was destined to
Re:Brilliant, Holmes, brilliant! (Score:4, Funny)
It isn't a water problem, it's a stupid people problem.
But people are mostly made of water, so now you have a stupid water problem...
Parent
Re: (Score:3, Funny)
Re:Whose energy are we stealing? (Score:5, Informative)
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.
Parent
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.
Re: (Score:3, Insightful)
My understanding of the fresh water/salt water system is that there is negligible temperature differential, that they're relying entirely on
Re:Whose energy are we stealing? (Score:5, Insightful)
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.
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Re:Green, renewable power (Score:5, Informative)
As such, any time we find a new source of power, you can damn well bet nature has gotten there first, and that our exploitation of said power will have negative consequences for the species already using it.
This sentiment of yours is dangerous in the sense that it is wrong yet rational enough that too many people could believe it.
Nothing was using the energy stored in uranium or oil until we got around to using it. And neither us nor any other creature is harnessing e.g. the energy of deuterium and tritium contained in seawater. Nothing is even using the energy of the sun shining on the desert.
Another problem with your idea: energy cannot be really "used", it can only be directed elsewhere. Sooner or later every form of energy will change into heat. We cannot stop this, but before it takes place we can transform energy into other forms to do something useful. Example: when the sun shines on the desert, it is converted to heat straight away. But when we put solar panels there, we can redirect a part of the energy to our homes and use the energy from the sun there, where in the end it will also be turned into heat.
I could go on about how humans are not artificial, but part of nature, but the main premise of your post is already invalidated so I'll stop.
Parent
Re: (Score:3, Interesting)
Here's the problem. Gravity is only interested in moving stuff in one direction, down. At some water will have to move against the gradient. Does the process produce enough energy to do that? If it does, how much water do you need in how much space, but just as importantly, what is the rate of production?
Oh, we'll put it on the coast, people say. Do the mixing reservoirs have access to the ocean? Good luck with the tides.
Re: (Score:3, Interesting)
I think you need to consider this more deeply.
You need two water sources, fresh and salty. The chambers are flushed alternately from each source. The only way this happens naturally is if you use the tides. Which gives you a total of 1 cycle a day.
Nature is not going to do all of the work. At some point, water needs to be moved against a gradient.