Solar-powered desalination system requires no extra batteries

[terramars]

This is a questionable way to present what's an excellent project and hopefully soon to be commercialized technology. The big deal here is it's a presumably installation ready application of EDR for desalination instead of RO which most systems use. This is a big deal because the membranes use electricity instead of pressure as the filter, which means everything can run at low, normal plumbing, pressures instead of the crazy high pressure RO stuff. For seawater it's borderline whether or not it will match RO for performance, but for lower salinity groundwater and industrial wastewater, it should be significantly higher performance for the same power as well as lower maintenance and capex.

The no batteries thing is basically irrelevant to the innovation, and in fact Genius Water already offers no battery RO systems, also with questionable benefit (as well as being difficult to work with).

I run a solar and water focused EPC in East Africa and will hopefully be working with these guys in the future when they're off the ground with a commercial system. The potential is extremely high, particularly if the maintenance overhead and operational complexity can come down in practice.

[ricksunny]

It sounds lime an MPPT on the supply side, with an ideal load-point tracking on the demand side. My understanding is that there are controllers (including for solar water pumping in the East Africa market) that pursue this. The concept applies more generally to systems where the load presented is configurable by system plant parameters, such as flow-rate & height.

[hedora]

Yeah; the solar part is really questionable. In an installation without batteries, they’d need an additional large tank to store excess daytime output.

Without such a tank, they’d need to somehow power the thing at night, which means a big battery, just like RO.

Also, the article suggests the power input needs to be steady and they use a computer to run it at higher rates when the battery would be charging.

Assuming there is a small battery or power grid (as both systems require), you could oversize an RO system and then change its duty cycle to keep the batteries at (say) 80% to prevent the solar production from curtailing. Round-tripping electricity through our home battery loses about 20%.

So, the “advantage” boils down to two questions that the article doesn’t answer: (1) what are the relative energy efficiencies of this system (in theory) vs RO? If the new system is 20% worse, RO wins, regardless of this optimization (2) what is the relative equipment cost vs. max throughput? (Since both setups assume oversizing to get better solar utilization).

I’d also like to know if the new system requires plastic, since the RO membrane probably leaches all sorts of nasties into its output.

I do like the fact that they are focusing on brackish water. We have this problem even in the coastal US (in the form of water softener output), and I’m sure they could sell a premium alternative to RO as a way to get scaling advantages on the manufacturing of the equipment.

[elzbardico]

Unlke some comments are implying, this is not a solar distiller with "additional steps". It still uses far less energy than distillation as it doesn't involve phase changes.

It uses Electrodialysis, which is a mass separation process in which electrically charged membranes and an electrical potential difference are used to separate ionic species from an aqueous solution and other uncharged components.

[SoftTalker]

Can't a lot of the phase change energy in distillation be recovered by using incoming water to cool/condense the distilled water vapor?

[bastloing]

That's great news! Now if they can solve the same problem with sea water, California, Arizona and Nevada can reduce their reliance on the Colorado river and grow more crops. It is only a matter of time before it's solved. Great work, MIT!

[ttyprintk]

It’s a great application, but electrodialysis on seawater takes more power—-so much that distillation is competitive. The use-case chosen is remote freshwater wells which suffer from naturally-occurring arsenic. I can only think of a few others which can’t have heavy batteries.

[dylan604]

Getting water to heat/boil is much less impressive than coming up with a solve for the left over salt/minerals. Solve that, then I'll join in the "Great work"

[fred_is_fred]

Even if you could do this you'd have to pump the water back uphill to NV and AZ.

[computergert]

I wonder what this means for the calculations outlined here: https://www.sustainabilitybynumbers.com/p/how-much-energy-do...

[asah]

great article but it tries to (ahem) separate drinking water from other uses, which doesn't seem practical:

- in the poorest places, they can't afford desal. - in non-poorest places, most water is delivered by unified piping systems due to cost and labor efficiency. Schlepping water in bottles and buckets is nuts, though I can see it turning into the next weird fad in exercise or robotics.

[JCharante]

This seems.. simple?

[netbioserror]

While it's an odd example for this place, I can bring up self-loading firearms (semi-automatic or automatic in today's terms) as a demonstration. Modern self-loading firearms are VASTLY simpler than the early attempts a century ago. They're an excellent example of engineering evolving under economic pressures.

Late 19th and early 20th century attempts at self-loading firearms were often ridiculous in their concepts; huge component counts, lots of tiny mechanisms, strange attempts at extracting recoil and gas energy, everything under the sun. The mechanisms engineers were crafting in literal garage workshops are stunning in their variety and staggering in their watch-like complexity. Some were genuine works of art.

Then the M1 Garand, the SVT-40, and afterwards the AK (under the economic pressures of WW2) demonstrated how much room there was to simplify and give various components double duties. Now, most modern automatic weapons derive from those designs, and the improvements since have been in the materials engineering: Stronger, lighter, thinner, and generally reducing the amount of steel to the minimum necessary.

[WJW]

Many useful things are simple. Not all of them exist yet.

[jvanderbot]

Yeah if the main insight is "you can run electric dialysis desalination on variable input power" they sure did a lot of dressing it up.

[black_puppydog]

https://www.nature.com/articles/s44221-024-00314-6

[cryptonector]

> “The majority of the population actually lives far enough from the coast, that seawater desalination could never reach them. They consequently rely heavily on groundwater, especially in remote, low-income regions. And unfortunately, this groundwater is becoming more and more saline due to climate change,” says Jonathan Bessette, MIT PhD student in mechanical engineering. “This technology could bring sustainable, affordable clean water to underreached places around the world.”

Uh, that's just going to increase the rate of acquifer depletion.

[surajrmal]

Reminds me of cloud based batch jobs. We must have many more opportunistic workloads similar to this one.

[voidUpdate]

This sounds a lot like the concept of a solar powered distiller... As in, heating a container of water with the sun, evaporating the water and then cooling it down to convert it into fresh water...

[marcosdumay]

It's not. It's an electrodialysis desalinator. I have no idea what in the article gave you the idea it was thermal.

[black6]

But with extra steps and points of failure.