Osmotic membrane produces 1 megawatt per square meter!

[Fungus]

This is being reposted like crazy today:

http://phys.org/news/2016-07-electricity-salt-three-atoms-thick-membrane.html

The potential of the new system is huge. According to their calculations, a 1m² membrane with 30% of its surface covered by nanopores should be able to produce 1MW of electricity

[firewalker]

As I understand it, at the moment it doesn't produce anything close to 1 Mwatt.

Alexander.

[Kilrah]

I hate that trend of taking any slightly positive result of something that barely works at a tiny scale in a lab and instantly blowing it up to [insert scale that results in huge impressive numbers here] to be able to declare [field] will be revolutionized soon™ before it's even known whether the thing can be scaled up... 

[T3sl4co1l]

Yes, let's make square meters of 3-atom-thick films, that are robust against environmental forces and biological contamination...

I also don't think water has that kind of energy density to begin with, even if you saturate it with salt.  It certainly doesn't get that hot, and I can't see a square meter with anywhere near enough volume of water flowing over it being able to deliver that much power.  But I haven't run the numbers.  I do know there is entropy, and voltage, associated with concentration: but it's quite small, on the order of 10s mV.

Tim

[Kleinstein]

The theoretical potential of osmotic pressure is not that small. As a rough estimate one get something like 20 bar of pressure - so effectively having something like a 200 m virtual drop for rivers of fresh water flowing in a salty ocean. The energy is coming from the temperature - so make the water cooler by about half a degree.

The trouble is the membrane. Also scaling could be tricky as the membrane needs to stand a pressure difference in the 20 bar range - relatively easy at µm scale, but difficult at meter scale.

I also very much doubt the numbers. For that energy density the water would have to flow at 100 m/s. Don't think this will happen - not large scale, but also not in the micro scale.  So maybe someone mixed up mm and miles.

[Tomorokoshi]

Well, I think they could get 1 mW per square meter.

[Red Squirrel]

They're going to need some nanosuperconductors to transport that massive amount of power throughout the array too.

[Marco]

Presumably you'd put the membrane on an open cell foam as support, so it would only be unsupported over a small distance.

[CatalinaWOW]

You can learn all you need about the science underpinnings of this article when the author describes tidal power stations as implementations of osmatic power.


I was fascinated for a while by the potential of using the density difference between fresh and salt water for power generation.  Run a long pipe from the surface to an appropriate depth, put an osmatic membrane at the bottom and watch the fresh water come pouring out the top.  Then I ran the numbers.  The physics works, but the ratio of power produced to capitol cost is laughably small.  Throw in the required periodic maintenance on the deepwater end and it is only good for a scam fundraising project.  It might make a useful desalination approach for locations that have a very deep marine trench close to the shore, but I didn't find any suitable locations that also needed freshwater in my quick survey.

[gardner]

The third paragraph:

Salt ions travel through the membrane until the salt concentrations in the two fluids reach equilibrium. That phenomenon is precisely osmosis.

OSMOSIS is the movement of the solvent (water) across the membrane.  The solvent is neutral and nothing weird happens to the charge across the membrane.  They are proposing that ANIONS and CATIONS move through the membrane differentially to create a charge separation.  I have no idea whether that is feasible, but in any case it's not what OSMOSIS is about.

[Towz]

Not osmosis. Dialysis. The energy seems to be coming from brownian motion (thermal energy), which is indeed the base for dialysis.