[HN Gopher] Solar-powered desalination system requires no extra ...
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Solar-powered desalination system requires no extra batteries
Author : bentocorp
Score : 109 points
Date : 2024-11-17 22:06 UTC (1 days ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
| JCharante wrote:
| This seems.. simple?
| WJW wrote:
| Many useful things are simple. Not all of them exist yet.
| jvanderbot wrote:
| 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.
| devilbunny wrote:
| Desalination that can start and stop, increase or decrease
| activity, without messing anything up is the secret sauce
| here.
|
| Not going to do that with reverse osmosis systems.
|
| That said, with merely brackish input water, I'm wondering
| how many problems this really solves. Drinking water, sure,
| but you have to get rid of the concentrated brine at the end
| and it's still groundwater that can be overdrawn.
|
| However, if v 2.0 can effectively desalinate ocean water, it
| would be huge for islands and coastal areas.
| marcosdumay wrote:
| The main insight is "we've spent the last years tuning a
| dialysis controller to work well on variable input power".
|
| I imagine the paper has the actual parameters, so you can
| build upon their work.
| netbioserror wrote:
| 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.
| aidenn0 wrote:
| Off topic, but it seems like self-loading pistols took a
| weird detour; at least for cartridges too powerful for
| blowback operation. There are all sorts of weird delayed-
| blowback systems that were popular between WW2 and 1980-ish,
| and now 9mm and larger seems to almost exclusively use a
| 1911-style short-recoil system.
| netbioserror wrote:
| It's simple, reliable, and quite necessary. Pistol
| chamberings feature heavy bullets in straight-walled, short
| cases. Blowback bolts are always extremely heavy to
| compensate for those attributes. Beretta and FN are famous
| for resisting Browning short-recoil for alternatives like
| rotating barrels and locking blocks. But they pay for those
| tradeoffs: Heat buildup, wider slides/frames, extra
| complexity, and more. Browning short recoil is the best of
| all worlds. Replacing rotating links with simple cam cuts
| sealed the deal.
| aidenn0 wrote:
| I actually think the gas-delayed blowback in the HK P7
| hits "simple and reliable" as well, but it has the huge
| downside of putting very hot gasses very close to where
| you handle the gun.
| MisterTea wrote:
| The AK copied the STG-44 Sturmgewehr (literally "assault
| rifle, this is where the design and name comes from) which
| was revolutionary in design and abilities. Prior to the
| assault rifle solders weapons were either accurate long range
| rifles with high power cartridges or close range inaccurate
| sub-machine guns firing low power pistol cartridges. Military
| researchers realized that most solders were average people
| and could not make full use of the high power and accuracy.
| The solution was an intermediate cartridge that combines the
| longer range and accuracy of the rifle cartridge with the
| smaller profile and lower recoil of a sub machine gun. Now
| you have a weapon that can hit at a distance or go auto and
| fight close quarters. Huge advancement and advantage for the
| solders wielding such weapons. Kalashnikov was directly
| inspired by these abilities and developed the AK in response.
| Just about every modern "Assault rifle" is descended from the
| STG-44, not the AK.
| bastloing wrote:
| 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 wrote:
| 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.
| ttyprintk wrote:
| Here's a state-of-the-art portable prototype with
| pretreatment: 0.3 l/h at 20W:
| https://news.ycombinator.com/item?id=31243621
| terramars wrote:
| This isn't really accurate, they're targeting industrial
| wastewater yes but they are working with and have tested
| brackish water up to several thousand TDS. They had a working
| EDR system for drinking water installed in Gaza until
| relatively recently and several in India as well. I'm also
| skeptical they can make it work with seawater, but it
| absolutely works with undrinkable brackish water in many
| other cases too.
| fred_is_fred wrote:
| Even if you could do this you'd have to pump the water back
| uphill to NV and AZ.
| dylan604 wrote:
| Just install some additional solar powered pumps along the
| way
| fred_is_fred wrote:
| The amount of energy needed to pump enough water for ag
| uphill is insane. Well beyond "just" throwing some solar
| panels out there. If it was that easy we'd pump Mississippi
| water into west Texas (which there was a plan to do in the
| 60s with nuke plants, but I cannot find the name right
| now).
| dylan604 wrote:
| i left off the /s as to me anytime someone starts a
| comment off with "just ____" is usually a farcical idea.
| like just remove the salt from water and boom, done.
| fred_is_fred wrote:
| Hah! It can be a very HN comment to "just" something
| especially around physical engineering.
| aidenn0 wrote:
| Could you save on pumping energy by sending the water to
| underground aquifers rather than the surface?
| bastloing wrote:
| Ok, so it's two problems to solve. Get on it MIT!
| itscrush wrote:
| No, start with modifying the Colorado River Compact and other
| underlying agreements to allow more upstream retention than
| is currently allotted.
| dylan604 wrote:
| 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"
| SoftTalker wrote:
| > the left over salt/minerals
|
| There is a commercial market for salt -- and for stuff like
| treating roads in the winter it doesn't have to be very
| clean.
|
| Otherwise, disolve it into the local waste water stream and
| discharge it back into the ocean.
| dylan604 wrote:
| If this was the case, then why is the briny residue left
| after desalination always the thing that gets pointed back
| to being a big negative of desalination?
|
| Either it's not as big of deal as people suggest, you are
| wildly underplaying it, or somewhere in between. I've never
| felt that the argument against being the cost to heat the
| water was a strong one since salt water pretty much means a
| coastline which tends to have steady wind and sun. The
| biggest hang up has typically been putting that brine back
| into the ocean.
| surajrmal wrote:
| Reminds me of cloud based batch jobs. We must have many more
| opportunistic workloads similar to this one.
| black_puppydog wrote:
| https://www.nature.com/articles/s44221-024-00314-6
| voidUpdate wrote:
| 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...
| black6 wrote:
| But with extra steps and points of failure.
| EricE wrote:
| I think you are missing the key point: it takes a fraction of
| the energy vs. the solar desalinization you are referring to.
| marcosdumay wrote:
| It's not. It's an electrodialysis desalinator. I have no idea
| what in the article gave you the idea it was thermal.
| yogurtboy wrote:
| I think their thought process was "It uses the sun to
| desalinate water, so it must be the same"
| elzbardico wrote:
| 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 wrote:
| Can't a lot of the phase change energy in distillation be
| recovered by using incoming water to cool/condense the
| distilled water vapor?
| elzbardico wrote:
| It would improve it a bit, but not enought to compete in
| terms of energy usage with dialysis or reverse-osmosis.
|
| Reverse-osmosis is absurdly efficient compared to
| distillation: a single 1X1 meter square solar panel can
| potentially generate 200 liters of fresh water per day.
| terramars wrote:
| 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.
| hedora wrote:
| 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.
| cryptonector wrote:
| Tanks are fairly cheap, and you'll need one anyways. But
| yeah, the solar angle is not what's interesting here. It's
| the electrodialysis.
| ricksunny wrote:
| 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.
| computergert wrote:
| I wonder what this means for the calculations outlined here:
| https://www.sustainabilitybynumbers.com/p/how-much-energy-do...
| asah wrote:
| 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.
| cryptonector wrote:
| > "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.
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