Electricity From Salty Water

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."

Comments

Economy is a Subset of Ecology

[weston]

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.

Re:Economy is a Subset of Ecology

[amRadioHed]

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:Economy is a Subset of Ecology

[gad_zuki!]

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.

Re:neat

[jbeaupre]

It produces less (laws of thermodynamics are a bitch). But you point out an interesting way to describe it to people. i.e. It takes energy to desalinate sea water, this process is sort of like running desalination in reverse to generate energy.

Re:Brilliant, Holmes, brilliant!

[Andy Dodd]

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.

Re:What about the fishies?

[man_who_was_thursday]

I suspect this could have a profound effect on environments where salt and fresh water mix gradually and where the mix changes with tidal flow. I live in Virginia, and I can't imagine this would work without significant environmental challenges to the coastal waterways like those that flow into the Chesapeake Bay.

Re:Brilliant, Holmes, brilliant!

[mrisaacs]

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 end up mixed into salt water would be used.

FTA: the real problem

[lazn]

"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!

Whose energy are we stealing?

[Marc_Hawke]

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 solar panels.

What do the hot/cold water exchange generators do? I would expect that pumping cold water from the ocean warms up the ocean...but that would be putting energy INTO the water instead of extracting it. So I'm a little confused. Lets just say it 'changes the ocean temperature'. That's enough to disrupt the ecosystem.

With this salty water thing. Whose energy are we stealing? If there's some sort of exothermic reaction going on in all river mouths, there's definitely something that's evolved to take advantage of that. Energy on the planet doesn't just SIT there doing nothing. (cept Oil...nobody uses Oil but us. :) ) What's the result of the environmental impact study? (I don't just mean habitat loss...I want to know who specifically was harvesting that energy.)

Re:Whose energy are we stealing?

[radtea]

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.

Re:Whose energy are we stealing?

[Late Adopter]

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:Whose energy are we stealing?

[cfa22]

There is no way windmills reduce the amount of wind so much as to affect things like seed dispersal. The area perpendicular to the wind velocity is enormous and windmills occupy a very small fraction of that. Windmills siphon a relatively small amount of the air's kinetic energy, most likely smaller than the amount of kinetic energy that ends up does nothing useful whatsoever.

Re:Whose energy are we stealing?

[smellsofbikes]

All the gravity-related sources of energy harvesting currently in use (at least that I'm aware of), which is to say hydroelectric power, rely on the same solar evaporation -> pure water running downstream process. They just extract it directly through turbines rather than through osmotic pressure. But it's still solar energy doing the heavy lifting, so to speak.

My understanding of the fresh water/salt water system is that there is negligible temperature differential, that they're relying entirely on the entropy of osmotic pressure, so I think the whole discussion of temperature is off-topic. TFA says nothing about temperature differential, only a sort of ion membrane system.

Re:Double Duty?

[AP31R0N]

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!

Re:Double Duty?

[Bandman]

How do you propose to get the water high enough at that point to fall into the ocean?

Re:What about the fishies?

[Chris Pimlott]

Don't bother. PETA and Greenpeace both called and said it'll kill too many endagered fish species.

Fish? Oh, you mean sea kittens.

And how much energy might we get from this?

[downhole]

I have mod points here, but I didn't see any other posts addressing this point, so I'll say it instead.

The big problem with all of these kinda wacky energy schemes (from the perspective of energy independence and global warming advocates who clamor for these things) is that none of them show any potential of producing enough energy to measurably offset the use of any of our major energy sources like oil, gas, coal, and nuclear. It may be cool and there may be a useful niche for it somewhere, but unless you can get at least gigawatts if not tens of gigawatts or more reliably, then it won't have any effect on our importation of fossil fuels or overall global carbon emissions. And there's also the question of how much other environmental damage and disruption would be caused by deploying something like this on a multi-gigawatt scale.

Re:Double Duty?

[omnichad]

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!