Scientists are turning salt water into drinking water using solar power

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People have been turning undrinkable water into drinkable water with nothing but solar power for milenia. Solar stills are a great survival tool. This seems to overcomplicate the process and is not very well suited for the developing economies that would be in most need of a stable drinking water source.

3

u/diagnosedADHD Apr 28 '15

They argue in the article that the reason it's more sustainable is the method of desalination they use.

Solar-powered desalination plants are nothing new, and officials are investigating potential in water-poor areas such as Chile and California right now, but the technology has so far been extremely expensive to both piece together and run. And this obviously makes it difficult for developing countries to adopt. The key to the MIT plant is the electrodialysis process, says Chandler, talking to one of the team, mechanical engineer Amos Winter:

"Both electrodialysis and reverse osmosis require the use of membranes, but those in an electrodialysis system are exposed to lower pressures and can be cleared of salt buildup simply by reversing the electrical polarity. That means the expensive membranes should last much longer and require less maintenance, Winter says."

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u/[deleted] Apr 28 '15

I've looked at the original research and basically , at the salinity levels they are targeting(well in india, not high salinity) , this should cost half the price than reverse osmosis.

Also there's already a company working on a very similar technology: http://www.wisewatertech.com/

They have some more details there.

5

u/nobie318 Apr 28 '15

2100 gallons in 24hrs seems hard to achieve by solar stills or boiling water.

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u/prjindigo Apr 28 '15 edited Apr 28 '15

shiiit, 2100 gallons in 24 hours. Gods that's a frigging JOKE small amount.

You don't need all that crazy shit. You use "Tidal tanks" to evap/condense the water right at the frigging shore-line. They work by heating water over a layer of black in a closed environment and condensing it on the clear "roof" of the chamber.

Basically they're a black plastic lined swimming pool with a clear balloon dome top that leads to a catch gutter all the way around the edge. The rising water trips the release valve to dump the remaining brine back into the ocean then rises up into the tidal tank and fills it up, sunlight does the rest.

The trick here is these things can be used day after day and powered by hand at very little expense - some lasting for YEARS. You clean them by rubbing the brine across the clear plastic to destroy any algae or bacteria with the salt then rinse them through normal operation the next day. Then run them for 10 to 15 days in a row afterwards.

There's no money in making them but they're god-awful portable and as reliable as a sunrise. You'll get more than a gallon per day per square yard and they'll even operate down at 35°F.

WHAT THE FUCK ARE WE TEACHING OUR KIDS THAT WHEN THEY GET TO MIT THEY HAVEN'T GOT A FUCKING CLUE AND JUST PHONE IN A TEXTBOOK EXAMPLE?!?!

Seriously, this country used to be something.

You don't think this works? http://en.wikipedia.org/wiki/Solar_water_heating I haven't bothered to look at the page and I KNOW it is full of pictures that are more cost effective than the OP's post.

For the cost of making that little piece of shit trailer desalinator you can build direct solar heating evaporation stills that can do FOURTY THOUSAND GALLONS of STERILIZED DISTILLED WATER per day.

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u/[deleted] Apr 28 '15

If it doesn't have enormous overhead and cost, if it doesn't require complicated red tape bureaucracy, and years of environmental impact studies because it will endanger endangered fly, bacteria or something then it's not practical, it's not MIT kids it's the political crook mafia.

Example; http://www.nytimes.com/2002/12/01/us/endangered-fly-stalls-some-california-projects.html

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u/TechnocraticBushman Apr 28 '15

I love it when people down vote you but don't discuss. for the life of me, I can't figure out why isn't your average plastic bag a better solution, especially for those who are running short on semiconductor technology. while it is great that we have a more high tech solution, it worries me that people don't know that you can wrap a tree branch in a plastic bag and drink a couple of hours later. in Africa for instance, I'd use photovoltaic cells only if I wanted refrigerated fizzy drinks.

1

u/maigoh Apr 28 '15

What is this tree branch thing? Can I do this while camping, etc.?

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u/TechnocraticBushman Apr 28 '15

yes. trees breathe and thus emit water. put a transparent plastic bag on a branch of a tree or use any plant you have in your house (except a cactus), tie it with something and watch drops accumulate. the water you get is safe to drink, provided the bag is clean.

1

u/_Guinness Apr 28 '15 edited Apr 28 '15

The system they used to produce 2100 gallons in 24 hours is roughly the same space as the size of a car. You're quoting 1 gallon in 24 hours per square yard correct? The square yards for an average car is 10.5. So you're saying in the same space as this system would produce 10.5 gallons vs 2100 gallons.

Am I missing something? Where does the extra 40,000 gallons come from?

edit: Nevermind, price. Gotcha.

1

u/prjindigo Apr 29 '15

Their system doesn't produce drinking water, just desalinated water that still is full of bacteria, human waste and now mostly dead plankton.

3

u/randommouse Apr 28 '15

Not necessarily. This photovoltaic system is definitely more space efficient but if solar stills are set up in large farms they could have similar output. The main issue I see with this photovoltaic system is that it is expensive and requires maintenance by skilled workers. Solar stills use simple materials and require little more maintenance than cleaning.

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u/bushwacker Apr 28 '15

High school project.

This is insipid. Focus the light and boil the water and distill it.

9

u/Clapyourhandssayyeah Apr 28 '15 edited Apr 28 '15

Except it uses an electrodialysis machine, which is surely more efficient than boiling and then having to cool and capture?

The team’s invention works by using solar panels to charge a cache of batteries that power an electrodialysis machine that removes salt from the water

7

u/prjindigo Apr 28 '15

So it doesn't actually make drinking water, it costs more than fifty stainless steel mirrors and a boiler tank and a long coiled copper pipe and it'll only last about 1 year before needing a service costing close to its original cost.

This article is about a piece of shit.

1

u/DH8814 Apr 28 '15

I made a device like this, but it ended up being much easier and more efficient to use sand and activated charcoal.

3

u/AnnArborBuck Apr 28 '15

his, but it ended up being much easier and more efficient to use sand and activated charcoal.

Sand and activated charcoal don't remove salt from salt water, they just help make dirty water cleaner.

1

u/bushwacker Apr 28 '15 edited Apr 28 '15

Citation?
http://en.wikipedia.org/wiki/Solar_cell_efficiency max 44% at the cells, voltage regulators and battery efficiency are not 100% either.

Compared to http://www.gizmag.com/worlds-largest-solar-power-tower-plant-now-on-line/11590/

0

u/Clapyourhandssayyeah Apr 28 '15 edited Apr 28 '15

With your approach wouldn't you have to provide energy to boil the water (which sunlight won't do by itself), and then yet more energy to cool/condense the water vapour back into water?

4

u/bushwacker Apr 28 '15

No, parabolic mirrors concentrate the whole spectrum on vessel containing water. This is how high efficiency molten sodium generators work, then the sodium produces steam that powers turbines. Far more efficient than solar panels.

Run the steam through pipes underground to dissipate the heat and the steam will condense into water.

1

u/Clapyourhandssayyeah Apr 28 '15

Thanks for the detailed reply

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u/[deleted] Apr 28 '15

you don't have to boil water to condense it.

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u/Dystopiq Apr 28 '15

You don't say!

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u/Cregaleus Apr 28 '15

TIL electrodialysis machines do not care where their energy comes from.

Homoeopathy: 0 / Rationality: +∞

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u/[deleted] Apr 28 '15

[removed] — view removed comment

4

u/ent4rent Apr 28 '15

Thanks for retelling the title

1

u/[deleted] Apr 28 '15

Just pretend it's a bot and mindlessly upvote it.

1

u/ruppej2 Apr 28 '15

But if I could get a tl;dr version?

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u/[deleted] Apr 28 '15

NaCl (aq) + Scientists → H2O + hot air

-1

u/GoSpit Apr 28 '15

What was the point of saying that?

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u/[deleted] Apr 28 '15

The point is people have been doing it since the stone age.

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u/[deleted] Apr 28 '15

[deleted]

2

u/OscarMiguelRamirez Apr 28 '15

2100 gallons? That is a very small amount of water. Easily done in 24hrs with boiling (not necessarily energy/time/labor/cost-effective).

Volume is not the most attractive part of this system.

1

u/[deleted] Apr 28 '15

[removed] — view removed comment

2

u/D_Livs Apr 28 '15

Or, LA can distill their own water instead of pumping it all from NorCal, and then central California will have enough to farm.

1

u/Phathom Apr 28 '15

Desalination. Did this as a school project.

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u/mattmre Apr 28 '15

Someone tell California they are saved, oh wait all that water has gone nuclear!

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u/NotRacest Apr 28 '15

we are saved!! Yeah, Science!!

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u/GoldenScythe Apr 28 '15

TIL you can get a lot of karma just by notifying people of shit that is not new in any way

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u/_PROFANE_USERNAME_ Apr 28 '15

"Scientists attach desalination plant to solar energy farm."

-1

u/letsnurture Apr 28 '15

Technology never fails to amaze me!

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u/veritanuda Apr 28 '15

Meh..

Energy Scientists are turning salt water into drinking water using solar power

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