New membrane unlocks energy from chemical difference between fresh and saltwater

https://www.sciencemag.org/news/2019/12/rivers-could-generate-thousands-nuclear-power-plants-worth-energy-thanks-new-blue

by vo2maxer • 7 years ago

144 77 7 years ago

sciencemag.org

kitsuac• 7 years ago

It sounds like a non-renewable energy source which changes the natural flow of the water permanently. Isn't there bound to be negative environmental effects?

aedron3• 7 years ago

I dunno, the article said that one square meter of the membrane could power 400 homes. And they believe the material can be made even more effective with a proper manfucaturing process. That would not seem to disrupt waterflow. I personally think this sounds incredibly promising.

orbifold• 7 years ago

If you use a small membrane there will be basically no way that a sufficiently large gradient between the two sides exist to produce meaningful amounts of electricity. This article is total bullshit even if the material science is nice.

bradyd• 7 years ago

the article said that one square meter of the membrane could power 400 homes

The article was updated to correct this number, it was actually 3 instead of 400.

vanderZwan2• 7 years ago

a non-renewable energy source

The sea will remain salt and as long as rivers will flow the ion potential will exist along the coastline. Are you referring to other parts of the method?

jandrese3• 7 years ago

Really this is a roundabout way of harnessing the power of the Sun. In this case the energy used to liberate water vapor from the ocean.

When you think about it this way, all of our energy sources are just repackaged solar except for nuclear.

nkrisc2• 7 years ago

Non-renewable? All that salt in the ocean isn't going anywhere and we'll have fresh water as long as the water cycle continues. You could even use grey water waste from fresh water that was originally desalinized for human use.

I mean, you could say solar is non-renewable because the sun die one day. After all, there is a finite supply of solar energy.

tathougies2• 7 years ago

This is actually a form of solar energy anyway because it is the sun that provides the initial energy to separate the water, and move the water into the atmosphere against gravity.

munk-a• 7 years ago

This doesn't sound terrible but it will have effects on the ecosystem similar to hydro at least - blocking fish migration paths, reducing river flow rate and potentially causing algae blooms, fish die-offs or water toxicity increases as sediments are disturbed in fun new ways.

All that said, it's certainly miles above either coal or natural gas.

vanderZwan2• 7 years ago

If researchers can scale up the postage stamp–size membrane in an affordable fashion

Not to be a downer, but this feels like it is in the "possibly long-term solution" department. Which is definitely important to investigate, don't get me wrong!

cagenut• 7 years ago

at a meta level, these types of articles with a ridiculous headline and without any meaningful pictures or diagrams are infuriating.

w/r/t the actual scientific discovery, i'm fascinated by how much of solving the overall energy/carbon problem is coming down to 'nano' scale material science and engineering. does anyone know of a better media venue for materials science developments that isn't just some loud guy reading wiki articles to a webcam?

rkangel• 7 years ago

What I find infuriating is units like '30 megawatt hours per year'. Why not just tell us how many megawatts?

cbmuser• 7 years ago

Because you can just divide 30 by 365*24 to get the actual power which would be 3 Kilowatts or 0.003 Megawatts.

dienciebsiwbsi2• 7 years ago

It's 3.4 kW, enough for two toasters. So not nearly enough for 400 homes; their math is wrong.

navaati• 7 years ago

Obviously because that’s not a lot of megawatts. For the lazy, that’s 3.42kW ;).

cygx• 7 years ago

It's common to measure total electricity production of a nation (eg 650 TWh for Germany in 2018) that way...

vo2maxer• 7 years ago

The findings were reported recently at the Materials Research Society meeting and have not been published yet. Here is the abstract: https://meetings.aps.org/Meeting/DFD19/Session/B36.6

pjc503• 7 years ago

IEEE spectrum is kind of OK for informative popsci?

aedron3• 7 years ago

So many jaded comments! This is incredibly cool. The 'breakthrough' (if you can talk about that at such an early stage) is a few simple materials engineering hacks:

The nanotubes were easy. Cetindag says the lab just buys them from a chemical supply company. The scientists then add these to a polymer precursor that’s spread into a 6.5-micrometer-thick film. To orient the randomly aligned tubes, the researchers wanted to use a magnetic field. The problem: BNNTs aren’t magnetic.

So Cetindag painted the negatively charged tubes with a positively charged coating; the molecules that made it up were too large to fit inside the BNNTs and thus left their channels open. Cetindag then added negatively charged magnetic iron oxide particles to the mix, which affixed to the positively charged coatings.

When the researchers applied a magnetic field, they could maneuver the tubes so that most aligned across the polymer film. They then applied ultraviolet light to cure the polymer, locking everything in place. Finally, the team used a plasma beam to etch away some of the material on the top and bottom surfaces of the membrane, ensuring the tubes were open to either side. The final membrane contained some 10 million BNNTs per cubic centimeter.

When the researchers placed their membrane in a small vessel separating salt- and freshwater, it produced 8000 times more power per area than the previous French team’s BNNT experiment.

zozbot234• 7 years ago

So many jaded comments! This is incredibly cool.

I agree. You could use the process to power a desalination plant, and make even more freshwater!

marcosdumay3• 7 years ago

You need a membrane permeable to negative ions too for that.

In fact, I think you'll need that membrane for electricity generation too. Otherwise you will only get to make a single layer of it, what is underwhelming.

But it is a large breakthrough.

whateveryou381• 7 years ago

From the article the pad produces 30 MW-hr/year/m2. This implies that you need 292533 m2 for this to produce more power than a 1 GW nuclear reactor.

For an idea of the scale of this water based power reactor that would produce this energy, I compare to the amount of space required for a large surface area reactor such as a CO2 chemical scrubber. These reactors have effective surface area of about 500sq meters of surface area per 1 meter3 of volume. This implies that you are looking at a reactor that has about 600 meters3 of volume. This is smaller than a typical olympic sized swimming pool, which is about 1700cm3.

I don't know if these comparisons are fair, but it implies that there are some questions about heat removal and how it might be as dense of a source as claimed.

jve• 7 years ago

The article has since been corrected.

it produced four times more power per area than the previous French team’s
*Correction, 6 December, 11:30 a.m.: This article has been corrected to accurately reflect how many homes a blue membrane could power and how much energy per area it produces.

aazaa• 7 years ago

The article unfortunately does not use the more common term for the "blue energy" principle: "osmotic power."

The Wikipedia article on osmotic power explains the physical principles better:

https://en.wikipedia.org/wiki/Osmotic_power

The Science article didn't explain very well why an estuary is required. The idea is apparently to have two bodies of water - with differing salinities - in close proximity. This happens near estuaries. The ocean provides water with high salt content. The outbound river provides water with low salt content. Those two sources of water in close proximity can either be used where they are or pumped into even closer proximity.

Place a membrane (like the carbon boron nanotube devices discussed in the article) between the two pools of water with different salt content. They may be housed inside a power plant or outside. Then capture the energy released from the movement of ions through the membrane. There appear to be different approaches for that last part.

In other words, the saltwater and freshwater sides of an estuary provide the two charge compartments of a very large battery.

The breakthrough here is a way to manufacture the high-performance membranes needed provide a path for the ions through this system.

asdfman1233• 7 years ago

Do you need an estuary? Can't you just divert river water, put it next to salt water, and then you can produce power?

In fact, the only place "estuary" is used in the article is in the image caption, and I assume they used it because it's tangentially related and it's a pretty picture. Really you just need a pool of salt water and a pool of freshwater, and those two things are easy to get where rivers flow to the sea.

aaronblohowiak• 7 years ago

those two things are easy to get where rivers flow to the sea.

Isn’t that an estuary?

ChuckMcM• 7 years ago

Any river would work. An interesting application for LA or the Bay area

aljungberg2• 7 years ago

One wonders how quickly these pores will become clogged over time. If the membrane deteriorates fast, the energy cost of producing more membranes continuously needs to be factored in.

The article headline is pretty weird, by the way. So this technology can generate “thousands of nuclear power plants worth of energy”? But then in the third paragraph it sounds like they mean to say if you installed this membrane in every estuary in the world, then it’d beat 2000 nuclear plants.

It’s like saying there’s more water in a cup than in a bathtub, as long as the cup is the size of a car.

aedron3• 7 years ago

the researchers estimated a single square meter of the membrane [...] could [...] power more than 400 homes.

aljungberg2• 7 years ago

Even the smallest nuclear power plant in the states generates 582 MW — enough for 95 000 homes.

I’m not saying this isn’t a cool membrane. I’m making the point here that the comparison to 2000 nuclear power plants seems arbitrary.

pjc503• 7 years ago

.. or in real units, 30MWH/year = 3.425 kW. Which is quite a lot. That's what I get from about 10 square meters of solar panels, or one electric kettle running continuously. Seems implausibly high, I would move the decimal point over by one and naively guess it has the same energy density as solar panels.

Khoth• 7 years ago

Either the power or the number of homes in the article is completely wrong. 30MWH/year powering 400 homes is 8.6 watts per home. Implausibly low, unless "homes" is a typo for "phones".

pharrington• 7 years ago

Three homes. Please update your comment.

*Correction, 6 December, 11:30 a.m.: This article has been corrected to accurately reflect how many homes a blue membrane could power and how much energy per area it produces.

hinkley• 7 years ago

It's too bad RO is still so inefficient, or you could store purified water with surplus grid power as a cogeneration strategy. Drinking water or power, depending on which is in shorter supply.

amluto2• 7 years ago

I suspect that pumped storage is rather more energy-dense than this. I suppose both could be combined.

martimarkov• 7 years ago

Can anyone explain why the fresh water is needed? The article mentions that the ions in water are not bound to one another so why can’t we just use salt water entirely?

mnw21cam• 7 years ago

There has to be a difference in the water on either side of the membrane. The energy is being extracted from the entropy of the system. Currently, fresh water flows into the ocean, where it mixes with salty water, and goes from a highly ordered system (separate fresh and salty) to a disordered system.

We generate energy from heat the same way. It is no good to just have heat. To generate electricity or motion, you also need cold. It is the transfer of heat from hot to cold, making the hot cooler and the cold warmer, that allows us to make use of it.

Practically speaking, this membrane lets positive ions through, but not negative ones. So, you put fresh water on one side, which has few ions, and salty water on the other side, which has plenty of both. Then, the positive ions flow through, and you end up with water full of positive ions on one side and water full of negative ions on the other side. That is electricity that can be directly tapped.

marcan_42• 7 years ago

Where does the energy go when it is not being extracted with this method?

I understand that the energy is extracted from the movement of ions between reservoirs of different salinity. If you're just letting the two sides mix, as they do naturally, where does the energy go instead? Is it released as heat?

marcosdumay3• 7 years ago

It converts thermal energy into usable electricity (that is, the water gets cooler), at the cost of the increased entropy in the mixing of fresh and saline water.

Accujack• 7 years ago

Also, the environmental cost of keeping river estuaries blocked by impermeable membranes so you can maintain the gradient of salt/fresh water.

dwiel• 7 years ago

I wonder if this could work in places with no ocean nearby just using rain water and rain water with added salt. Would you need an obscene amount of new salt/rain water?

jandrese3• 7 years ago

The energy cost of acquiring the salt would probably make it uneconomical. Plus you have to get rid of massive quantities of brackish water without a convenient ocean nearby.

Maybe it could be used at the Great Salt Lake, but otherwise the options are limited.

asdfman1233• 7 years ago

One potential problem: you derive energy from converting freshwater to salt water. What do you do with all that salt water? You could cook it in the sun to evaporate out the water and start the process over again, but you've basically made a solar energy plant.

The cool thing about using membranes near rivers and the ocean is it uses the ocean as your solar energy plant.

You could also place this device near natural dead seas to produce power... but that's basically what the article is proposing.

driverdan• 7 years ago

If researchers can scale up the postage stamp–size membrane in an affordable fashion

That's a huge "if." This type of development happens all the time and usually that "if" never comes true.

logfromblammo• 7 years ago

Imagine how much power could be generated at the place where the Colorado River empties into the Gulf of California!

If you didn't understand the implication, I think that in the future we will need the fresh water more than we will need to get power from making it more salty. The Colorado River has only rarely reached the ocean since 1960. It's like the Aral Sea. Human activity uses the entire river.

TheSoftwareGuy• 7 years ago

This is exactly what I was thinking. There are those who believe that the next world wars will be fought over access to fresh water. This technology seems to make that future even more likely

amluto2• 7 years ago

It might make sense to use a technology like this to extract power at a sewage treatment plant.

alistproducer2• 7 years ago

Can anyone provide a link to the paper? I've googled and haven't been able to find anything.

bcatanzaro• 7 years ago

Industrializing our most environmentally sensitive areas by controlling all the water flow in wetlands... What could possibly go wrong?

8bitsrule• 7 years ago

Following are original paper and phys.org article about (a similar project?) at EPFL in 2016. They use a molybdenum disulfide membrane.

'Single-layer MoS2 nanopores as nanopower generators'

https://www.nature.com/articles/nature18593

'Electricity generated with water, salt and a three-atoms-thick membrane'

https://phys.org/news/2016-07-electricity-salt-three-atoms-t...

Teknoman117• 7 years ago

2.6 TW/h with 100% global resource utilization, which amounts to 1/60th of the world's energy usage in 2013...

New membrane unlocks energy from chemical difference between fresh and saltwater

Related Stories