A new form of hydroelectric power – no dam needed

From Stanford University: A unique idea that has great potential (pun intended). The only catch is that availability and quality of fresh water is one of the biggest environmental concerns now, way ahead of global warming.

Stanford researchers use river water and salty ocean water to generate electricity

The initial state of the battery developed by Yi Cui, with two electrodes immersed in fresh water. Purple and orange dots represent positively and negatively charged ions, respectively. In Step 1, a small electric current is applied to charge the battery, pulling ions out of the electrodes and into the water. Step 2, the fresh water is purged and replaced with seawater. Note much higher abundance of charged ions in the salt water. Step 3, electricity is drawn from the battery for use, draining the battery of its stored energy. Ions return to electrodes. Step 4, seawater is discharged and replaced with river water, for the cycle to begin anew. Courtesy of Yi Cui, Stanford University

Stanford researchers have developed a battery that takes advantage of the difference in salinity between freshwater and seawater to produce electricity.

Anywhere freshwater enters the sea, such as river mouths or estuaries, could be potential sites for a power plant using such a battery, said Yi Cui, associate professor of materials science and engineering, who led the research team.

The theoretical limiting factor, he said, is the amount of freshwater available. “We actually have an infinite amount of ocean water; unfortunately we don’t have an infinite amount of freshwater,” he said.

As an indicator of the battery’s potential for producing power, Cui’s team calculated that if all the world’s rivers were put to use, their batteries could supply about 2 terawatts of electricity annually – that’s roughly 13 percent of the world’s current energy consumption.

The battery itself is simple, consisting of two electrodes – one positive, one negative – immersed in a liquid containing electrically charged particles, or ions. In water, the ions are sodium and chlorine, the components of ordinary table salt.

Initially, the battery is filled with freshwater and a small electric current is applied to charge it up. The freshwater is then drained and replaced with seawater. Because seawater is salty, containing 60 to 100 times more ions than freshwater, it increases the electrical potential, or voltage, between the two electrodes. That makes it possible to reap far more electricity than the amount used to charge the battery.

The mouth of the Amazon River, where the world’s largest drainage basin flows into the Atlantic Ocean. A location such as this, where fresh and sea water mix, is a good spot for generating electricity with Yi Cui’s new battery. Credit: NASA

“The voltage really depends on the concentration of the sodium and chlorine ions you have,” Cui said. “If you charge at low voltage in freshwater, then discharge at high voltage in sea water, that means you gain energy. You get more energy than you put in.”

Once the discharge is complete, the seawater is drained and replaced with freshwater and the cycle can begin again. “The key thing here is that you need to exchange the electrolyte, the liquid in the battery,” Cui said. He is lead author of a study published in the journal Nano Letters earlier this month.

In their lab experiments, Cui’s team used seawater they collected from the Pacific Ocean off the California coast and freshwater from Donner Lake, high in the Sierra Nevada. They achieved 74 percent efficiency in converting the potential energy in the battery to electrical current, but Cui thinks with simple modifications, the battery could be 85 percent efficient.

To enhance efficiency, the positive electrode of the battery is made from nanorods of manganese dioxide. That increases the surface area available for interaction with the sodium ions by roughly 100 times compared with other materials. The nanorods make it possible for the sodium ions to move in and out of the electrode with ease, speeding up the process.

The manganese dioxide nanorods used to make the postiive electrode of Yi Cui's new battery that generates power by using the salinity contrast between fresh and salt water. Credit: Courtesy of Yi Cui.


Other researchers have used the salinity contrast between freshwater and seawater to produce electricity, but those processes typically require ions to move through a membrane to generate current. Cui said those membranes tend to be fragile, which is a drawback. Those methods also typically make use of only one type of ion, while his battery uses both the sodium and chlorine ions to generate power.

Cui’s team had the potential environmental impact of their battery in mind when they designed it. They chose manganese dioxide for the positive electrode in part because it is environmentally benign.

The group knows that river mouths and estuaries, while logical sites for their power plants, are environmentally sensitive areas.

“You would want to pick a site some distance away, miles away, from any critical habitat,” Cui said. “We don’t need to disturb the whole system, we just need to route some of the river water through our system before it reaches the ocean. We are just borrowing and returning it,” he said.

The process itself should have little environmental impact. The discharge water would be a mixture of fresh and seawater, released into an area where the two waters are already mixing, at the natural temperature.

One of Cui’s concerns is finding a good material for the negative electrode. He used silver for the experiments, but silver is too expensive to be practical.

His group did an estimate for various regions and countries and determined that South America, with the Amazon River draining a large part of the continent, has the most potential. Africa also has an abundance of rivers, as do Canada, the United States and India.

But river water doesn’t necessarily have to be the source of the freshwater, Cui said.

“The water for this method does not have to be extremely clean,” he said. Storm runoff and gray water could potentially be useable.

A power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power, according to the team’s calculations. That would be enough to provide electricity for about 100,000 households.

Cui said it is possible that even treated sewage water might work.

“I think we need to study using sewage water,” he said. “If we can use sewage water, this will sell really well.”

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March 29, 2011 12:27 pm

This is one of those, “why the hell didn’t I think of that?” moments.
It may not be commercially viable, but it would have been an easy graduate thesis.

March 29, 2011 12:35 pm

I wrote a book in 2003… and it included the discovery of this technology.
Although in my book, the discovery was of the ancient world…

March 29, 2011 12:36 pm

i know how to fix this. We will use Barrie Harrop’s windmill driven reverse osmosis plants to generate the fresh water so that we can generate the electricity. A veritable perpetual motion machine of the first kind.

March 29, 2011 12:39 pm

There is a small little problem… they need to pump the water up from the ocean. This is where there electricity will go into.

March 29, 2011 12:40 pm

“The battery itself is simple, consisting of two electrodes – one positive, one negative – immersed in a liquid containing electrically charged particles, or ions. ” and coated with slime and zebra mussells.
“They chose manganese dioxide for the positive electrode in part because it is environmentally benign”. But we may have to consider lead pipes, copper sulfate coatings or add clorine to the diverted river water.
“But river water doesn’t necessarily have to be the source of the freshwater, Cui said.”
We can use the water from a de-salinization plant just as well!
““I think we need to study using sewage water,” he said. “If we can use sewage water, this will sell really well.”, or potatos, last year my daughter brought home a potato battery, really cool, we could power all of Prince Edward Island with just a couple of tons of nails some wire and the potatos in the ground! Free electicity.

March 29, 2011 12:45 pm

I’ve only skimmed so far, and I’ll be looking for educational comments, but this sounds crank to me–perpetual motion machine style. They admit it has limits, but I’m not sure I see any potential at all.

Gary Pearse
March 29, 2011 12:53 pm

Many years ago I wondered if Great Salt Lake could be made into a giant battery. It’s not as goofy as I thought.

Harry Bergeron
March 29, 2011 12:53 pm

To me the obvious use would be refining aluminum from bauxite.
This take huge amounts of DC if I remember correctly.
There are large losses in conversion to AC, transmission, and
conversion back to DC which could be avoided.

March 29, 2011 12:55 pm

Actually, mods, if you don’t mind indulging me for a moment, here’s the part of my book (yes, 2003) that is relevant:

“It’s so obvious, I can’t believe neither of us thought of it. I have the images on a webpage. I want you to see them, then see if you come to the same conclusion I did.”
He gave me the address and I typed it into my computer. There were the grainy but colorful results of the scan.
“Wow,” I whistled. “You’re right, it’s so obvious. But what about control?”
“Tell me what you see.”
“I see a salt cavern, possibly the remains of an ancient sea, with metallic plates embedded throughout. Water no doubt trickles through, making it a gigantic natural battery.”
“Excellent. Can you estimate the current and voltage we are looking at?”
“No,” I said, smiling. “Assuming the red ones are copper and the blue ones are, what, silver? Gold?”
“Gold, maybe. My own estimate is that this is several tens of thousands of amperes, and by the number of plates it would be about ten thousand volts. Direct current.”
“This is larger than the entire visible pyramid complex,” I said, amazed.
“They probably selected the location for the pyramids based on the availability of this cavern,” he said. “If we had thought of this, we might be running towns and cities on natural battery power.”
“It does seem rather obvious, doesn’t it? Then again, the sheer cost of the metals might be high.”
“Not compared to a nuclear plant,” he pointed out.
“But, what turns it on and off? Surely this has not been consuming power for five thousand years, there would be corrosion and crud on the plates.”
“At the moment, I have no answer, but now we know where the power is coming from. Can you imagine, an almost free power source underground, the only pollution is a bit of ionized saline leeching into surrounding subterranean areas. We could self-sustain our electrical needs for millennia.
“Centuries, anyway,” I said, thinking. “We’d have to maintain the plates from time to time.”

March 29, 2011 12:56 pm

85% efficiency still says they are only getting out 85% of the energy they put in. Thermodynamics dictates this isn’t the panacea they claim. It could make an excellent storage system for surplus power on the grid though and used to even out generation capacity, because 85% seems pretty good for battery efficiencies.

March 29, 2011 1:00 pm

Nearly all riparian estuaries have brackish water resulting from tidal exchanges. What sort of infrastructure will be required to transport of pure fresh water to plant where the mixing and generation occurs? Can it be cost effective?

March 29, 2011 1:03 pm

I seems to me that all they are doing is charging a capacitor in low conductivity water and then rapidly discharging it in the high conductivity sea water. Also, by using this type of material, they may be producing concentration cells.

March 29, 2011 1:05 pm

“… Cui’s team calculated that if all the world’s rivers were put to use, their batteries could supply about 2 terawatts of electricity annually – that’s roughly 13 percent of the world’s current energy consumption.” [emphasis added]
Seems like a pie-in-the-sky projection to me, for a result that is self limiting. I cannot imagine even 10% of the world’s rivers being put to such use; then we have massive constructs providing no more power than wind turbines.

Don K
March 29, 2011 1:06 pm

From my notes on energy sources:
===Osmotic Power===
Osmotic power is a label for various techniques for exploiting the fact that water containing salts is denser than fresh water. This difference can be exploited to generate power when the less dense fresh water is mixed with saltier water. In the case where rivers are the source of the fresh water, the mixing would take place anyway, so the power is essentially free — other than the possibly considerable cost of the generation facility.
Osmotic power is renewable and does not release significant carbon. It may however be disruptive to the environment where many species that currently live in the brackish water transition zone between fresh and salt water might be threatened.
The amount of power available is unknown with some sources claiming a potential for 1.6 to 1.7 Twh (over what time span?) This appears to work out to a “sticker” capacity of about 900GW (Note: These numbers do not appear to make sense), but it seems fairly unlikely that actual generation will reach anything like those levels. Currently there is a single 4kw pilot plant in operation in Norway.
The article isn’t very clear, but I suspect that either the fresh water has to end up salty or the salt water fresh. If not, it sure looks like a violation of conservation laws. A perpetual motion machine as others have said.

March 29, 2011 1:14 pm

“unfortunately we don’t have an infinite amount of freshwater”
Yeah, it keeps running downhill into oceans ….
“Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan.”

March 29, 2011 1:17 pm

Given that most places where fresh and salt water mix are subject to tidal oscillations anyway, wouldn’t it be simpler and more efficient to build tide-powered generators? And on the same subject, why is nobody using the pressure of tidal flows to drive osmotic desalination systems?

March 29, 2011 1:19 pm

Maybe a good option for Fjordland, but pretty useless everywhere else because of environmental constraints. In researching tidal power options as an electrical engineer, I found out that most coastal areas have at least 7 distinct stakeholders each of which has veto power over projects.
Essentially, the technology is irrelevant because regulations will prevent it from even being tested.

Jeff Carlson
March 29, 2011 1:23 pm

nice experiment that ignores the energy costs of moving the salt and fresh water to the lab …
in the real world I expect alot of losses for water transport (both ways, you’re not going to store it locally after its is used) …
pie in the sky …
I worked on a project in school that used the differences in water temperature in the ocean (surface vs hundreds of feet down) to vaporize ammonia, run it thru large turbines and condense it for reuse … sure it could generate power … but trying to scale it up would be a very different issue …
a solar cell generate free electricity as well … try powering an auto plant with them …

Steinar Midtskogen
March 29, 2011 1:32 pm

A working prototype for this kind of power plant has already been build in Norway.

March 29, 2011 1:39 pm

“… They achieved 74 percent efficiency in converting the potential energy in the battery to electrical current, but Cui thinks with simple modifications, the battery could be 85 percent efficient…”
Valves, pumps, lifting mass (water) etc.
Where these items considered in the efficiency calculations? I’m guessing “no.”
This is essentially an echo of Ray’s post above. He sees also sees the problem.

March 29, 2011 1:44 pm

Since this idea relies on the difference between salt and fresh water, would it also generate current with salt water of different concentrations on either side, vs. only salt & fresh?
At first glance, it seems to me that it would work, although somewhat less efficiently.

Ken Harvey
March 29, 2011 1:44 pm

This could work. I’m going to give it some thought and see if I can devise a contrivance that will push sea water up hill, with a zero energy requirement. Of course, once I have got my contrivance working properly we won’t need to mess around with batteries!

March 29, 2011 1:54 pm

I’d think that using the sun to distill some salt water would be a solution to the problem of fresh water – you’d still have to remove the excess salt from the distillation equipment.
TANSTAFL in any case.

March 29, 2011 2:07 pm

Steinar Midtskogen says:
March 29, 2011 at 1:32 pm
“A working prototype for this kind of power plant has already been build in Norway.”
And it cost a gazillion and produces enough energy to warm a cup of coffee, if i remember correctly. Fits perfectly to Dogbert’s fake green breakthrough press releases.

March 29, 2011 2:08 pm

On a casual read – it seems rather illogical to me! As others have commented it doesnt look like it could be very efficient but my first thoughts were actually environmental based. Like, what happens to the seawater and freshwater afterwards – how do the ions replace their charge ‘taken’ by the battery? As I recall my basic conservation of energy law – I am wondering where in the electrochemical chain will the effect of ionic/charge removal cause an eventual problem?

March 29, 2011 2:23 pm

The brainiacs always come up with such fanciful and wonderfully (expensive?) and equally applicable as W.E. Coyote finds the A.C.M.E. inventions.
Just create a sales pitch, like so: Lose weight, keep in shape, power the city lights, and save the planet!
Let the unsuspecting hippie, for statistics in this particularly well researched area has it that mostly the hippies will be attracted to the aforementioned sales pitch so no civilians will be hurt, climb into the caged wheel, then, with Flash-envious speed, just stuff three peeled red thai hot chilies up his bum and slam the door shut.
Sit back and try and figure out who’s whining the most, the hippies saving the planet or the generators.
Just don’t go for the truly green energy with ecological hydroponically grown green chillies, they just don’t have the same energy potency. :p

Bob Diaz
March 29, 2011 2:30 pm

Simple and practical, which is why all the environmentalists will be against it.

March 29, 2011 2:35 pm

why do you need to move water uphill? The freshwater is always flowing down to the ocean, to refill the battery you could pipe it(the freshwater) from upstream and at an angle from the battery, an angle to get the battery out of the mixing zone of where the river enters the ocean,then when you have charged up the battery you could just let ocean currents flush out the fresh water maybe a series of barges anchored in a line

George E. Smith
March 29, 2011 2:37 pm

let me guess, this works better than sticking a copper wire and an iron nail in a lemon or orange; and way better than an apple; right !! ??
So per million gallons of FRESH water :be my guest on the salt water; take plenty; it’s cheap ! How many megaWatts peak, or MegaWatt-hrs of electricity do I get. I’m pretty fussy about what I do with my fresh water.
Come to think of it, why couldn’t those California Central Valley farmers use their old salted up dead land, to make a huge salt water battery; it wouold work great evbery tijme we get a deluge period like the present, and have some fresh water we want to pollute for more juice.

Luther Wu
March 29, 2011 2:42 pm

manganese nodules litter the ocean floor

George E. Smith
March 29, 2011 2:42 pm

So far as I am aware, the only way you can get lower on the stored chemical energy Totem Pole; or Food Chain, if you prefer that metaphor; than H2O from burning the abundant supplies of native Hydrogen on Earth, is to add salts to the H2O. That about gets you down to bedrock for your Totem Pole.
And I see that Infinity iws now smaller than it used to be; we din’t ever have an infinity of anything; or even of everything; and now we have an infinity of salt water, and we want to make more. Simply Wunnerful !!

March 29, 2011 2:45 pm
It's always Marcia, Marcia
March 29, 2011 2:52 pm

Something I have wondered, if the Hoover Dam was broken by an earthquake how much flooding would it do, and for how many miles down river?
I’m not trying to be alarmist. I’m just wondering. Anyone know?

Another Gareth
March 29, 2011 2:55 pm

Why would you bother to collect sea water from the Pacific and fresh water from a lake when you could demonstrate the effect easily enough on a kitchen table?
Draining the ‘charged’ fresh water surely destroys the electrolytic cell. If it worked as the diagram suggests you ought to be able to produce electricity just sticking the electrodes in salty water. Perhaps that is the actual effect they are noticing, something like this: Salt water air battery

Luther Wu
March 29, 2011 3:01 pm

It’s always Marcia, Marcia…
that could never, never happen there in never, never land.

CRS, Dr.P.H.
March 29, 2011 3:03 pm

Why not make a whole bunch of these instead?

Bob Maginnis
March 29, 2011 3:19 pm

I heard about the potential energy between salt and fresh water in about 1982, and it isn’t perpetual motion, because to would require about 900 feet of head pressure to reverse the change from fresh to salt water, to desalt the previous fresh water from the river.

March 29, 2011 3:24 pm

I would be nice if pro AGW and deniers etc could debate like this

jack morrow
March 29, 2011 3:27 pm

The G M volt works about as good as this project will.

A G Foster
March 29, 2011 3:29 pm

If the chemistry has been tested, that’s all we need. You don’t have to move water, you just move the batteries up and down–river water floats on the surface for many miles out into the ocean–dozens of miles in the case of the Amazon. The batteries could be positioned on a slowly turning wheel on a floating platform. But I think the temperature differential between shallow and deep water holds more promise for large scale generation. There’s more ammonia than precious metals.

March 29, 2011 3:32 pm

Rossi’s Energy Catalyzers will produce 15 kilowatts continuously for 6 months on a 200g charge of nickel and hydrogen. Replaced twice a year, it will generate 131.4 Mwhrs/yr. World electricity consumption in 2007 was 17,109,665,000 MWhr. Using a 33% efficiency factor to convert E-Cat heat into electricity using the Carnot cycle would require just 174,000 tons of nickel powder (much of it recyclable since all of it would not be converted into copper). Annual world production of nickel is about 1,400,000 tonnes, so about 15% of the world’s nickel production is all that’s needed to generate practically all the electricity consumed by mankind, even when factoring in a 30% transmission loss.

March 29, 2011 3:32 pm

Use the melting arctic/antarctic ice… :o)

March 29, 2011 3:35 pm

Well, solar energy produces molecular motion which creates friction which produces heat. – And as we all know, heat is pure energy so I cannot see any flaws in this one.

March 29, 2011 3:37 pm

Why not just put paddle wheels on your sewer outlet and recuperate some of the energy the city uses to pump the water up your pipes.
In any case, a galvanic cell can be built between clean and salted water. The only problem is that the pure water gets contaminated via the electrolytic bridge. You can even measure a potential between two saline solutions having different concentrations, and of course once both solutions have the same concentration, the difference in potential is zero.

March 29, 2011 3:40 pm

“A power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power, according to the team’s calculations. That would be enough to provide electricity for about 100,000 households.”
The Fraser River in BC has a minimum flow estimated at 867 m-3/s and a maximum flow of 6970 m-3/s.
How big is this plant going to be if you need to divert so much water from a river.
Essentially you almost need to divert a really big river to get a 1000MW.
The fish won’t be happy.

March 29, 2011 3:43 pm

Following up on this idea of generating electricity when you flush…
Think about it this way, a city’s water reservoir can produce electricity since the energy is accumulated in term of height and mass. Now multiply that by the number of toilet reservoir and you get a very big water reservoir. If you take into account the added mass when you flush, we are talking serious megawatts here.

Michael Penny
March 29, 2011 3:51 pm

50 cubic meters per second of water to power 100,000 households is 792,516 gallons per minute, or 11,412 gallons per household per day. That is about 1.5 MW for each 10 feet of lift plus friction losses for the pumping of the water.

March 29, 2011 3:57 pm

Apologies from straying from the topic but this just caught my attention:
I wonder how CAGW related papers alone compare.

Lady Life Grows
March 29, 2011 4:03 pm

Energy flows wherever there is a gradient of any kind–hot air to cold regions (wind), water flowing downhill, etc.
This won’t solve all the world’s energy problems, but it will be practical to build in some places. And that is good enough.
But only carbon fuels can green up the world’s vast deserts.

Richard S Courtney
March 29, 2011 4:15 pm

I think several commentators have

Richard S Courtney
March 29, 2011 4:19 pm

I think several commentators have missed the point. As windfarms demonstrate, the technology does not need to work, to be economic or to provide electricity in useful amounts for it to harvest large profits from subsidies.
Indeed, this technology could be even more profitable than windfarms because it would do even more environmental damage than windfarms (that cover the countryside in concrete for their foundations and roads to access them) so ‘greens’ will campaign for it to get even larger subsidies.

Gary D.
March 29, 2011 4:20 pm

Being a hopeful optimist I find this very interesting, the skeptic in me says, but wait.
First, if a place in an estuary were found where the salinity of the water is dramatically less when the tide is out than when it is in, then wouldn’t the efficiency of adding and removing water to and from the battery be as high as what the paper claims? You just let the river do all of the work.
But how much difference would there need to be in the water’s salinity to make this effective?

March 29, 2011 4:21 pm

I’m going to build a giant treadmill powered by genetically engineered hamsters. I will fed them algae grown in ponds and fertilised with their own poo. It will be at least 250% efficient!

March 29, 2011 4:23 pm

CRS, Dr.P.H. says: “Why not make a whole bunch of these instead?
Just one single lemon the size of Phobos could supply 2/5 of the energy requirements of the United States! And the energy is practically FREE! We must build the Great Lemon Power Plant right away to save the Earth from Global Warming! Let us stand in front of the White House, join arms, and sing kumbaya! All together now…!

March 29, 2011 4:30 pm

Hmmm….. sounds suspiciously like perpetual motion at work here.
Got to pump the water, and have to account for the energy consumed in making the manganese dioxide rods.
Nice idea, though. Somebody has been thinking.

March 29, 2011 4:39 pm

stupidboy says:
March 29, 2011 at 3:57 pm
This might warrant a new thread. If you took away all the papers in the West attributed to AGW studies, then China is probably even or surging ahead of the West.
I hereby propose to change “Save the Planet” to “Save the Planet for the emergence of China”.

March 29, 2011 5:13 pm

The Panama Canal Zone, would be an excellent place to try this. Every time a ship moves through the locks, Millions of gallons of fresh and salt water are exchanged. Very little energy is required in the process and since it is already being done to move cargo, the electricity generated would cost only what is needed for constuction and infrastucture.

Doug Jones
March 29, 2011 5:32 pm

All scoffing aside, this system *can* work, and is an entirely reasonable extrapolation of battery and ion exchange systems. 100 MW from 50 m3/s comes to about 2000 J/kg, extracted from the entropy difference between salt and fresh water. That’s the energy equivalent of 200 meters of hydrostatic head, which is much *less* than what is needed to power reverse osmosis of fresh water from sea water, so the energy levels are in the realm of feasibility.
This is NOT a perpetual motion system; it takes a lot of energy to extract fresh water from seawater, the inverse process can inherently release a lot of energy. The tricky part is figuring out a good way to harness the entropy change- a naive method would be to run fresh water into a dry dock 200 m below sea level through water turbines, then allow it to diffuse into the ocean at that depth through osmotic membranes. The naive method would be a pain operationally because of silt and sludge in the fresh water, which would probably need perhaps a quarter of the concentrated fresh water to be pumped back up to sea level.
This electrolytic method is very very clever.

Dave Wendt
March 29, 2011 5:36 pm

It may be time to drag out a plan I came up back in my early high school days while sitting out a detention, brought on by one of the earlier instances of authority figures not appreciating my irreverent sense of humor. I envisaged a power generating system based on scaled up versions of this device.
My original plan called for lining the coasts with giant models, but I soon realized that any body of water of sufficient size would do, even large tanks. This means placement options are almost unlimited. I never had the opportunity, or desire really, to run the numbers for extractable power or optimum size, but given the tsunami of grant money swirling about novel energy schemes nowadays, it may be time to put in the effort. What do ya think?

March 29, 2011 6:47 pm

jonjermey says:
March 29, 2011 at 1:17 pm

“Given that most places where fresh and salt water mix are subject to tidal oscillations anyway, wouldn’t it be simpler and more efficient to build tide-powered generators?

This battery is totally useless but so is tide in most places; the head is far too small. Bay of Fundy and Horizontsal falls are possible exceptions but too far from consumption point.
And on the same subject, why is nobody using the pressure of tidal flows to drive osmotic desalination systems?
You probably mean REVERSE osmosis.
Answer: Because at the pressures achieved by tides you’d probably get several pico-grams of fresh water per century per Billion dollars of investment. Most people would consider this a poor ROI.
I admit that I didn’t read below the fold but some things are so absurd that the details don’t matter. Like, for instance, there is no need to read details of an experiment that demonstrates ESP. We know it can not work; the details are irrelevant.

March 29, 2011 6:53 pm

“A power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power, according to the team’s calculations.”
I have my doubts about the mechanism and the efficiency, but assuming this is not an early April Fool’s joke, there’s up to 500 cubic metres per second of pure water going into Doubtful Sound from the Manapouri Power Station in New Zealand.
The pure water is not really wanted in the Sound as it affects sea life, but it’s there now. Nobody will object if it’s used for another purpose, e.g. generating 1000 megawatts of power, or even if it was exported for people to drink! There’s a deep water port there. Let’s use it.

March 29, 2011 7:11 pm

I have so much fresh water near my house — SE Corner of Lake Simcoe Ontario — that I am pretty sure I could stuff rocks ion the underpants of every environmentalist on the face of the earth, stuff them in a nearby lake or river and never have to look at them again…
So I am not so sure about this shortage thing — at least not for my current purposes.

Jean Parisot
March 29, 2011 7:15 pm

Why wouldn’t a design use all gravity fed fresh water, and truck in salts to disolve in as needed for that half of the reaction? You could use it where ever freshwater head pressure wasn’t sufficent for hydro and could saturate the salty side for potentially better performance. Your super saline rinse would also discourage mussels and slime.
This could reuse industrial waste as well.

March 29, 2011 7:35 pm

This is a wonderful new battery technology but the technology of reverse electrolysis is not new. There have been experiments for decades and one plant is running in Europe. The water at the mouth of the river is a lost resource there. If you dam and divert up stream and leave no remaining flow then there are very adverse out comes for the ecology and fisheries. None of us would advocate completely blocking river flows.
However dams in general block fish population going up stream. This in turn block phosphorous and other soluble elements moving against the water flow leading to soil depletion and the need for fertiliser. The fish at the head waters becomes food for something, mostly insects and birds, on shore which in turn dies (or simply defecates) on the farm. Thus in a rich ecosystem phosphorous etc can go up hill.
Fish ladders work to solve the problem but their often species selective. More research is needed to make a much more species flexible fish ladder or lock.
A fish ladder around this technology would be essential if it blocked a full flow. In some places the river is more saline than the sea and the device could run on the sea water as the low salt input.
In the wet tropics where water is not limiting and flows to the sea are short, fast and continuous this technology will be very important. The catch is this is also where solar and micro hydro have the best prospects and biomass out does everything even oil; making the wet tropics the one place where energy should be abundant. Generally where it is not, you find old hammer and sickle symbols cast in cold war concrete.

Carl Chapman
March 29, 2011 7:46 pm

There are more ions in the saltwater than in the fresh water. Fair enough. I didn’t see the bit about how the positive ions get separated from the negative ions. Current isn’t going to flow until the opposite charges are moved apart. The diagrams don’t explain that bit.

March 29, 2011 8:16 pm

what do you think of this (if you have the time)?
“Fire from Water, hosted by Scotty from Star Trek”

March 29, 2011 8:22 pm

They need a different river than the Amazon. Last I heard, the surface water more than 100 miles out in the Atlantic was drinkable. Trying to put something in the open ocean permanently? i don’t think that has been solved yet.

Christoph Dollis
March 29, 2011 8:25 pm

What are you guys smoking? For example:

“I’m going to give it some thought and see if I can devise a contrivance that will push sea water up hill…”

Alternatively, you could build it at sea level, and have the fresh water come to you by gravity.

March 29, 2011 8:33 pm

I don’t see this as solving the worlds energy problems and there is a long way to go between a lab experiment and a practical power plant. However provided the source of fresh water is above sea level it should be possible to use the difference in density between fresh and salt water to avoid the need to pump either.
In principle you could have a cell that was open at the bottom and had a valve at sea level. Normally it would fill with sea water. Adding fresh water from the top with the valve closed would force the sea water out – the fresh water would rise above sea level because it is less dense. Then you open the top valve – the “overburden” of fresh water would run out and salt water would force the rest of the fresh water out of the cell. To avoid mixing you could use a floating piston with a buoyancy between that of the fresh and salt water to help separate the two – it would not have to have a perfect seal. Thus the only energy needed would be that required to open and close a couple of valves.
Assuming that treated sewage is sufficiently like fresh water this process could provide a useful byproduct for a treatment plant that normally discharges into the sea.

March 29, 2011 9:01 pm

The test of this is to use its own generated energy to swap out the salt water and freshwater. If it cannot produce enough energy to do this then it is an energy sink, not an energy generator.
Here’s a field test. Quite simple. Fly a fully assembled and tested system and with sufficient capacity for the task to the moon and let it heat itself to keep from freezing.
It won’t work as you can imagine. You don’t need to go to the moon to test it. It will stop working in your basement, too. It needs outside energy. In the electronics industry we call this a resistor.

Dennis L Kuzara
March 29, 2011 9:19 pm

So far no one has mentioned that aquatic organisms would very quickly clog up this system, rendering it useless.
About the hoover dam flooding: The great flood of 1905 by the Colorado river created the Salton Sea over a 2 year period, which was the impetus for building Boulder (now Hoover) Dam. The surface of the Salton Sea is currently 226 ft below sea level and covers about 376 sq mi or 241,000 acres, with a volume of 7,500,000 acre·ft, making it the largest lake in California. Much of Imperial County, CA is below sea level, with El Centro, CA (population 40K) about 40 feet below sea level. Since Hoover dam has an active capacity of 15,853,000 acre·ft, if the dam burst it would flood all the low lying areas with the water eventually draining into the Salton Sea, tripling the volume of the lake.

Mr Lynn
March 29, 2011 9:50 pm

As to “no-dam” hydroelectric power, I once spent some time in Eastern Nepal near a couple of swift-flowing rivers, pouring down from the Himalayas (the Arun and the Dudh Khosi), dropping thousands of feet in a few miles. It often occurred to me that you could divert some of those streams in canals along near-horizontal mountain contours, then drop the water down to the lower stream bed in the descending valley. You’d have turbines at the bottom of each run, generating electric power. If you built enough of those, you could power most of northern India. No dams needed.
/Mr Lynn

March 29, 2011 10:16 pm

Ah, the Salton sea – such a lovely place.
It is actually the site of natural as well as unnatural lakes, the current iteration being sustained by agriculture runoff. When I lived in SoCal it was still a good place to go to catch healthy corbina but that was in the 1960s. Now it is a toxic soup that, like an ill-mannered barista that re-uses old coffee grounds, absorbs and recycles life with the cold black heart of a grave robber and beckons from the flyways new death with the crooked finger of promise.
I think only the Berkeley Pit in Montana is more disgusting.

March 29, 2011 11:39 pm

Andrew30- Once the big red mud is generating potato power, perhaps the peislanders can export the juice all over Maritime Canada, enough electricity to warm the peas served beside the hot beef. Can you turn tobacco into batteries ? How about hake ?

March 29, 2011 11:49 pm
March 30, 2011 1:57 am

The roposed system is different to the one described in your link. Your version uses osmosis to generate a pressure difference across a membrane that can be used to drive a turbine. The system described in the main article uses the different properties of fresh and saline water to generate power by electrolysis. They are completely different processes.

John Marshall
March 30, 2011 1:57 am

We do have an inexhaustible supply of fresh water–as long as it rains.

Brian H
March 30, 2011 3:33 am

All of these diffuse low-density power schemes/sources have two things (at least) in common, massive hungers: real estate, and capital. That’s on the input side. On the output side, two more: uncontrollable variability, and minute output. “100,000 homes” with 100 MW sounds impressive, but that’s one hotplate per household. Actual averages are at least 5X higher, and peak loads 7-10X higher (for large samples).
And it would take 10 of those for a GW? Yawn. One half-ar*ed Nat Gas plant would outperform them at a fraction of the cost AND be able to match demand fluctuations. Plus make a moderate contribution to ending the planet’s CO2 famine!
But insane megaprojects that sap the resources of a nation or culture are nothing new. The Pyramids were a fine example, and on a smaller scale so is the Vatican. Or maybe you prefer the Aral Sea irrigation diversions?
For the moment, every wind turbine is a monument to Stupidity Rampant. Unfortunately, that’s the only capital crime in Nature.

Roy Milner
March 30, 2011 3:38 am

“John Marshall says:
March 30, 2011 at 1:57 am
We do have an inexhaustible supply of fresh water–as long as it rains.”
As long as the sun shines

March 30, 2011 5:47 am

Steinar Midtskogen says:
March 29, 2011 at 1:32 pm
> A working prototype for this kind of power plant has already been build in Norway.
That’s for an osmotic power plant – diffusion across a membrane increases pressure/lifts liquid and then you get energy out be a pressure differential.
The Standford thing is an electrochemical battery, the Norwegian thing is a hydro-electric process.

March 30, 2011 6:01 am

Doug Jones says:
March 29, 2011 at 5:32 pm

All scoffing aside, this system *can* work, and is an entirely reasonable extrapolation of battery and ion exchange systems. 100 MW from 50 m3/s comes to about 2000 J/kg, extracted from the entropy difference between salt and fresh water.

Thanks, your’s is the first comment that begins to explain how this critter works. I don’t have a good sense about how the voltage varies with the ion concentration. I think part of the problem is in the drawing. When the battery is charged in freshwater, the negative terminal pushes the ions into solution and positive ions would cluster around that electrode. When the fresh water is replace with salt water, then I guess the greater number of negative ions would force some to the electrode and force the voltage lower.
I think I’m still missing a lot – help?

March 30, 2011 6:09 am

George E. Smith says:
March 29, 2011 at 2:37 pm
> let me guess, this works better than sticking a copper wire and an iron nail in a lemon or orange; and way better than an apple; right !! ??
That’s electrochemical and the electrodes get consumed. This is ion exchange and no chemistry. I think.
> Come to think of it, why couldn’t those California Central Valley….
How about Utah’s Great Salt Lake vs spring runoff?

March 30, 2011 9:16 am

Maybe not a dam, but certainly a large diversion channel at the mouth of a stubstantial river.
I do like the commenters idea of using this on the freshwater discharge from seaside power plants… though wisdom of seaside power plants of a certain sort is questionable.

March 30, 2011 9:17 am

All the rivers run into the sea,
Yet the sea is not full;
To the place from which the rivers come,
There they return again.
I’m fairly positive that even if this form of power generation were to become economically exploitable, someone would discover a 1/4 inch long fish or a snail that would be endangered by it.

March 30, 2011 9:18 am

What happens when you charge manganese dioxide a nano-rods matrix in “fresh” water? The positive ions (H+) migrate to it and the voids fill with “fresh” water. The surface of the nano-rods is reduced to manganese oxide, manganese, manganese hydride, or some combination. The combination depends on the potential that is being used to charge this battery. What happens when you fill this charged battery with sea water? The negative ions will be attracted to this electrode. While the voids still contain “fresh” water, O– will react with the surface to form manganese dioxide. After the sea water diffuses into the voids, manganese chloride will form. Both “fresh” water and sea water contain other positive and negative ions in different concentrations that can poison the battery. How long do you expect it to have any kind of efficiency? How would it compare to Ni-CD?

March 30, 2011 10:21 am

Ric Werme says:
March 30, 2011 at 6:09 am
But Rick, the electrodes DO get consumed in this device by side reactions, and the cathodes by direct result of operation. The clues to the non-success of this device on scale-up are given in the professor’s own words. To paraphrase, “Looking for a better cathode” means, in layman’s terms, that the electrodes, even if silver, become sacrificial to side reactions. I’m sure the MnO2 pellets become sacrificial to side reactions as well. I am sure the first thing he would have done is “look” at all available electrode materials, which knowledge has been available for a hundred years. This is the big bugaboo of all electrode systems.
But these little fellers do not like Ag+ ions, or any heavy metal ion, including Mn, especially Mn(VII). If we come up with another corrosion resistant non-ferrous alloy, like Cr-Mn-Cu alloy, can yo imagine the outcry when Mn(VII) or Cr(VI) ions are detected in the water? By the way, Erin Brockovich became a millionaire over her claims (erroneous) that Cr(VI) caused cancer. These highly oxidized heavy metals also will kill beneficial bacteria and diatoms and, therefore, aquatic animals.
Of course, we could use RO to remove all these from the effluent water afterwards!
As for the osmotic membrane differential processes, the big drawback is also in materials.
For an RO unit to be kept operable, for example a laboratory demineralization unit, it has to be kept relatively sterile. The RO membranes are stored in formaldehyde to prevent bacterial breakdown. Bacteria love to eat polymers! Yum! I am sure the maintenance rate would be a little lower in a cold place like Norway, but those little fellers exploit every environmental niche in no time flat.

March 30, 2011 11:00 am

“Initially, the battery is filled with freshwater and a small electric current is applied to charge it up. The freshwater is then drained and replaced with seawater.”
OK, so we charge the battery, then drain out the charged electrolyte and replace it with another electrolyte …
Just in time for April.

March 30, 2011 11:14 am

Oh, right. We’re charging the electrodes, not the electrolyte. That could have been pointed out sooner.

March 30, 2011 11:28 am

There’s nothing new about this. And it’s just basic physics. It takes energy to free dissolved salt from water, so you get energy out when you salinate it. Just observe any river flowing into the sea and you will see a mist, which is the energy release from the salination. Big deal.
Where the concept entirely falls down is energy density. Rather coyly, the Stanford researchers decline to mention anything with respect to power density, i.e. the amount of extracted energy you get from the size of the infrastructure. If it’s like tidal power, the energy generated will be so low density that it’s uselessly uneconomic except for some tiny niche applications.
Nice try, Codetech, but salt domes form over millions or tens of millions of years. I really don’t want to have to wait about 10,000 years or so to accumulate enough charge to run my refrigerator. Take your salt dome, for example. Work out what the total energy release was and then divide it by the time over which it formed. You will come out with a very low number.

March 30, 2011 11:47 am

Some things to think about. If the process works like a storage battery, which it seems to do because of the necessity of charging the device, then there must be an electrolyte better than pure water which is a poor conductor. That would require some salt or acid to make it conductive. Then, since the charging puts ions into the electrolyte, either the electrodes begin as compounds of, say, sodium manganese dioxide and silver chloride or have sodium and chlorine absorbed in them. Then the charging with a high enough voltage might place just sodium and chlorine ions into the electrolyte in the latter case. In the former case maybe sodium, chlorine, silver, and manganese dioxide ions would go into the electrolyte. Would replacing the electrolyte with sea water with a possibly higher concentration of ions be able to discharge to a state where the electrodes have a composition different than their beginning state? If they could, then why not just begin with the electrodes and sea water and let the ions in the sea water react with the electrodes? Can one get more energy from a storage battery than than the energy stored in the battery just by changing the electrolyte after charging it? The terminal voltage may be different, but the total volts x amps x time = energy will be the same for charging and discharging with some heat loss.

March 30, 2011 12:53 pm

How many charge/discharge cycles did they demonstrate? How fragile (and expensive) are the manganese dioxide nanorods? What was the power required to charge the device? How much power was produced when the device was discharged?

March 30, 2011 12:58 pm

I have many inventions in the realm of physical chemistry, organic chemistry, and electronics. I think the failure of education in the patent area is much at fault here, and in promulgating these untested, futuristic ideas.
The international patent treaties are all unanimous in their demand that inventions satisfy three basic legal criteria: novelty, utility, and non-obviousness.
However, the overarching requirement is that an idea or concept is not patentable. One can only patent a thing. The thing has to satisfy the three criteria, but utility is the hardest nut to crack.
Remembering these facts, in my industry we were always admonished to work it out! “Engineer it out ahead of time” was a similar cry. What that meant was to identify the issues, problems and pitfalls, and solve them before the hypothesis was formulated. Then we would be required to run the violent gauntlet of challenges from our peers as we defended our theses, and we had better know the thing backwards and forwards ahead of time. In other words, we had better reduce our idea to practice before we exposed our vulnerable underbelly. (Reduction to practice is also a legal patent stipulation).
Because the grant process has become so lucrative to professors, they have been encouraged to skip steps. Pulling in money for the establishment is the goal. Ideas that had been previously relegated to Arthur C. Clarke or Frederick Pohl novels, now appear in academic circles. Then silly legislators fund these.
I think when someone floated the idea of the Dr. Seuss aerosol boat to make rain a year ago, an alert should have been sounded, but it wasn’t. I can’t blame them for making a living, but I hope that I may have had scruples, and charged ahead instead with something do-able. Who knows what the filthy lucre would have done to me!
Now, half-baked (or 10% baked) ideas are rampant. Even in the most prestigious schools, such as Cal Tech, is this charade going forward.
I feel sorry and worried for our science.

March 30, 2011 1:00 pm

Almost forgot…How many times were they able to charge one of their batteries using the discharge cycle from a second battery?

March 30, 2011 5:01 pm

John Marshall says:
March 30, 2011 at 1:57 am
We do have an inexhaustible supply of fresh water–as long as it rains.
Is there more water underground that above?

March 30, 2011 6:41 pm

The abstract for the paper at Nano Letters gives a more complex manganese electrode than the manganese dioxide electrode that the press release gives. It is sodium (y-x) manganese (x) oxygen (z) rather than my guess of sodium manganese dioxide in my previous post. I can’t get the paper because it is $35 for 48 hours online. As far as I can see, the efficiency is on drawing energy from the charged battery and not some kind of over energy device.

Ian B
March 31, 2011 6:07 am

The process is straightforward enough – geophysicists have been using something similar (Spontaneous Potential) since the Schlumberger’s discovered the effect in 1931. Occurs where a permeable rock and near impermeable rock meet and when cations can migrate into the impermeable rock but the much larger anions cannot.
The level is millivolts though.

March 31, 2011 7:47 am

More Press Release Science. Interesting but not anything to be excited about now. These types of articles used to fill the magazines, Popular Science and Popular Mechanics. Close to 100% of the touted breakthroughs never came to fruition. This one doesn’t look like it will fly either, but you never know.
When a press release falls back on such statements as ‘if all the world’s rivers were put to use, their batteries could supply about 2 terawatts of electricity annually – that’s roughly 13 percent of the world’s current energy consumption.’ it should set off your ‘pie-in-the-sky’ alarm. A two-year-old could tell you ‘no, no, no’ to that….there is simply no way anyone could claim to have carried out such a calculation from the proto-type battery design in the first place — it is just a made up number.
Shame on Standford for issuing such a statement — it is horribly embarrassing.

April 1, 2011 2:05 am

It occurs to me that the temperature of river water is usually quite different from that of sea water and therefore it would be much easier to extract energy using a simple Sterling engine. Of course, the problems with all these approaches is you got only a modicum of energy out with a lot of mechanics involved, whereas conventional electricity generation produces huge amounts of energy using a can with a fire lit underneath it.

May 5, 2011 11:56 pm

Lake Simcoe is awesome cottage country. The sky is like you wouldn’t believe in the city, you can actually see the Milky Way and smaller and smaller stars in between each other. Oh, look! There goes the satellite 🙂 Still, there are all usual stores nearby.

Anton m perera
May 9, 2011 3:30 am

Pl let me know the email of this person who invented this i like to try this in sri lanka.

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