Nanofluidic device generates power with saltwater | Hacker News Reader

Nanofluidic device generates power with saltwater

techxplore.com

48 pointsPaulHoule23 comments

The other day I was reading an article here about how one big problem with desalination plants is that they produce raw salt that increases the salinity of water near them. The consensus was "oh well the ocean is big", but if you put these things around where you're dumping the salt, at least you could get a little bit of the energy that you spent removing the salt back. So desalination becomes more efficient.

The raw salt can be recombined with returning wastewater, so on condition that the expenses are made to properly balance the flows the problem of brine disposal is not as big as usually depicted. However it is a very big problem if the authorities refuse to implement these appropriate measures.

A more explicit way this type of technology as depicted in the article could be used:

given access to multiple baths of different salinity, the energy recovered from mixing 2 strongly saline baths can be used to desalinate a less saline bath.

Consider the following map (2.7 MB png):

https://www.esa.int/var/esa/storage/images/esa_multimedia/im...

Clearly tracts of land largely separating seas of different salinity like Spain / Morocco [or for example Colombia, Panama, Costa Rica, Honduras, Mexico] have access to 2 distinct salinities.

So by recovering energy from dumping the Mediterranean salt into the Atlantic, the energy can be recovered to desalinate either Atlantic waters or other accessible baths of saline but lower salinity water, like a transformer.

A second point: if sufficiently scaled up it could provide baseload or buffer the mismatch between energy production and consumption, however one ought to reflect on the consequences on the local ecosystem if the water baths are not contained in man-made receptacles.

You could also just pump the brine into evaporation fields and harvest sea salt.

That was my first thought, too: "can this generate power with brackish water? Because, if so, there's a banger of a one-two shot with that previous article about desalinating water for drinking, and then hooking up the outflow to something that can generate power with it. That would be a pretty badass little home resource installation."

Thin channels + salt water; wouldn't this foul up with salt deposits almost immediately?

I may have a misunderstanding of how the ion flow is described. I always thought it was the water which moved from low saturation to high (which reduces the saturation of the solution), but on a molecular level that could just be too simplified an explanation.

So I guess if the ions are being pulled across the channel, molecules of fresh water would be coming over from the other side little by little and don't let the salt come out of solution?

In the Netherlands you can find a running experiment for power generation based on salt vs freshwater. It is using the osmotic pressure instead, but nevertheless, maybe interesting to know there is a pilot plant running and they acquired more subsidy to build a larger scale installation.

[0]: https://www.offshore-energy.biz/dutch-province-grants-e1-2-m...

isn't freshwater more valuable than to waste it this way?

The Netherlands has many rivers which run into the ocean. What do you suggest? That they bottle and store every drop if water that would otherwise flow into the ocean?

well if you pump them away for running through this nano-fluidic device, where you mix them with saltwater to get electricity... you could just as well store them.

Just build nuclear power plants to generate electricity if you need that. Those also don't only exist in simulations.

This tech might have better utility if it can be ran in reverse as a deslinanator. (though there are also proven technologies for that already)

Storing water is very different from placing a generator along where it flows.

This osmotic pressure technology doesn't exist just in simulations, it’s already deployed in practice. You appear to be confused.

I have no problem with nuclear energy but just bringing it up in a completely irrelevant context is obnoxious.

Generating electricity from salinity gradiens is very different from placing a generator along a waterflow

Store it for what and for that matter where? You're looking at making square kilometers of new reservoirs per day.

store it in plants and groundwater by using it for irrigation for example. I see this technology a solution in need of a problem to solve.

Using it for electricity production surely needs a lot of water treatment and pumping, a lot of energy investment, but not just submerging some magic membrane into the river deltas. It might have use in medical devices or some special niches, but not in the Netherlandish brackish waters.

Storing it in plants just increases the volume, since plants aren't pure water. Do you think transforming the environment into maximally dense foliage to store water is without energy cost or side effect? What's the point?

> store it in plants and groundwater by using it for irrigation for example

If there is one thing the Netherlands already has in abundance, it's greenhouses for agriculture.

Wow, what a good idea, please do get in contact with the government of the Netherlands and tell them about your genius idea to build canals and irrigation!

Simply genius

In some places you'd be right. But this is a river that would otherwise just flow into the sea. The two biggest rivers in the Netherlands have an average discharge of ~750 thousand liters of water per second. We can spare a few M3/sec for generating electricity.

then use that for cooling a nuclear power plant, which has meaningful power output. You cannot use this without water treatment and big pumping stations anyway.

You can use sea water directly for the cooling though, no need for freshwater.

It looks like they didn’t even build a PoC. All the results are simulated.

Most things are simulated before being built. It's an iterative process.

Their setup looks remarkably similar to my PhD work [0][1] (that included a PoC and simulation). We didn't do power generation, but there was significant electrical activity (nanoamps and millivolts per pore). If I remember right, even at the time there was ongoing research to use porous films to generate power from saltwater, but the ongoing issue was biofouling. Turns out it's really easy to clog a pore that is nanometer-scale.

[0]https://scholar.google.com/citations?view_op=view_citation&h... [1]https://scholar.google.com/citations?user=M-Zy8lkAAAAJ&hl=en...

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