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.
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.
> 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.
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.
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.
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.
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.
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?
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.
> 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!
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?
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?
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.
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?
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.
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?
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.
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.
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.
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
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?
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.
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.
[+] [-] aedron|6 years ago|reply
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.
[+] [-] whateveryou381|6 years ago|reply
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|6 years ago|reply
> 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.
[+] [-] zozbot234|6 years ago|reply
I agree. You could use the process to power a desalination plant, and make even more freshwater!
[+] [-] aazaa|6 years ago|reply
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.
[+] [-] asdfman123|6 years ago|reply
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.
[+] [-] aljungberg|6 years ago|reply
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.
[+] [-] hinkley|6 years ago|reply
[+] [-] aedron|6 years ago|reply
[+] [-] marcan_42|6 years ago|reply
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?
[+] [-] marcosdumay|6 years ago|reply
[+] [-] driverdan|6 years ago|reply
That's a huge "if." This type of development happens all the time and usually that "if" never comes true.
[+] [-] vanderZwan|6 years ago|reply
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!
[+] [-] 8bitsrule|6 years ago|reply
'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...
[+] [-] cagenut|6 years ago|reply
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?
[+] [-] vo2maxer|6 years ago|reply
[+] [-] rkangel|6 years ago|reply
[+] [-] pjc50|6 years ago|reply
[+] [-] martimarkov|6 years ago|reply
[+] [-] mnw21cam|6 years ago|reply
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.
[+] [-] kitsuac|6 years ago|reply
[+] [-] nkrisc|6 years ago|reply
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.
[+] [-] vanderZwan|6 years ago|reply
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?
[+] [-] aedron|6 years ago|reply
[+] [-] munk-a|6 years ago|reply
All that said, it's certainly miles above either coal or natural gas.
[+] [-] logfromblammo|6 years ago|reply
--
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|6 years ago|reply
[+] [-] amluto|6 years ago|reply
[+] [-] bcatanzaro|6 years ago|reply
[+] [-] dwiel|6 years ago|reply
[+] [-] asdfman123|6 years ago|reply
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.
[+] [-] jandrese|6 years ago|reply
Maybe it could be used at the Great Salt Lake, but otherwise the options are limited.
[+] [-] Teknoman117|6 years ago|reply
[+] [-] alistproducer2|6 years ago|reply
[+] [-] hockeybias|6 years ago|reply
[deleted]