New solar device makes desalinated seawater cheaper than tap water

Originally published at: New solar device makes desalinated seawater cheaper than tap water | Boing Boing


I made a solar still for a grade-school science fair out of wood and plexiglass, inspired by Voyage of the Mimi which we all watched in school. . I tested whether one painted black desalinated faster (not noticeably with my janky setup). So yeah, I’d like to think I had a small hand in this development.


So how much will they charge for it?


I am very curious about the numbers they’re claiming here. I’m very skeptical any time someone claims a bunch of individual small-scale devices can do something more efficiently than a centralized industrial-scale operation can.

Surely if this technology is really so revolutionary they could just scale it up to provide the tap water for a small municipality?


And then Qatar will built a hundred, a thousand or however many they need to provide tap water for the entire country.


Congratulations on your efforts. And, as a product of the 80’s, thank you for reminding me of the Voyage of the Mimi and my first exposure to science curriculum that was both fun and informative.


Them: How badly do you want this delicious fresh water?

Marlon Brando Don Corleone GIF by The Godfather


To me, based on the claims, it seems like this might be intended for small villages and homes. I really doubt this could be scaled to produce water in large scale, after all one of the biggest issues is not so much producing but what do you do with the highly concentrated toxic brine. But if this is at a small scale i don’t think it’d be as much of an issue


They claim it could make 4 to 6 liters per hour. Obviously that would only be when the sun is shining, but to be extremely generous let’s say they had good sun and were able to operate this device at an average of 5 liters per hour, 8 hours a day, 365 days per year. That would be 14,000 liters per year, which is a fraction of the typical per-capita residential water usage. In California residential water rates mean that much tap water would cost about $27. Difficult to imagine that this device can really be built cheaply enough and last long enough to save money on tap water, but like you said, it would be good to see what assumptions they’re making in their calculations.


Is this anything like the ~5 year cycle where some new tech start up discovers Peltier devices and think they can pull water out of the air in Africa or some other drought stricken land?

Color me skeptical that this will work at scale, and with out requiring power that makes it unfeasible.

We have desalination technology, it is just energy intensive.


This is supposed to be a passive solar system, and all of those have a fundamental limit of how much energy they can receive in a given area. The very upper limit for a 100% efficient system with no loss due to the atmosphere is the 1361 watts per square meter that the sun throws at us, and real world considerations make it much less in reality. I don’t know if this system is meant to get all the energy for evaporation from direct sunlight or if it also absorbs some heat from the surrounding air, but either way there are some pretty hard limits on just how much water you could get from a device of a given size.


You mean you’re doubting the same institution that brought us cold fusion?


Right. Like Peltier devices WORK - but the conditions need to be just right to be efficient enough to be useful.

If this device can’t desalinate water at scale, then it is an interesting experiment, not practical for real world applications.


The fact that it’s tilted is a clue that it might actually work. It sounds like the self-purging feature is the most important part. It also sounds simple enough that anyone could make their own if the details are published. Oh, wait, someone’s gotta get rich…


Did they test this on real-world seawater or just homemade saltwater?

Seawater contains a whole bunch of other stuff beyond salts - like algae and bacteria - that would quickly foul-up a unit looking something like the prototype. However, I wonder if it could be used to desalinate well water that has become contaminated?


There’s the rub.

Oh dear, another miraculous water device. Hopefully this one obeys the laws of thermodynamics.

Using energy from sunlight to evaporate water is time-tested.

The configuration of the device allows water to circulate in swirling eddies, in a manner similar to the much larger “thermohaline” circulation of the ocean.

This sounds like marketing bafflegab.

This might be where it doesn’t scale out of the lab without more work. With a solar-powered still, you have to buy a round-trip ticket: Once it puts enough energy into the water to turn it into vapor, it has to extract that same amount of energy to turn it back into liquid. The problem is how and where to dump that energy, otherwise the still will heat up and the water will stop condensing.

In the field, I think they’ll run into limits of how much energy they can get rid of with passive air-cooling, especially when the outside air is already hot.

Solving the salt-clogging problem is a good step.


The distinction reminds me a bit of the attitude of Green Building Advisor with going “off grid” for residential power. Essentially they argue it’s much more efficient to tie to the grid, and feed your residential solar and other sources into it. That gives you round the clock power, and if you have a utility with a decent flow-back rate (BIG “if” in the U.S.) you make out better than trying to mess with battery walls and such. Even better if your local system can switch over to giving you direct power if the grid goes down.

For small island of otherwise already isolated locations, this could make a lot of sense…


Will it filter out the nanoparticles of plastic?


Maria Telkes, who once taught and researched solar at MIT, would be happy (and maybe jealous). She also developed a passive solar still for the USNavy in WWII (which went into production only after the war was over).

I wonder if these people used any of Viktor Schauberger’s work on the effect of shapes, especially spirals, on water.