I think that any filtration system that works through evaporation/distillation like this would actually produce extremely clean water, but that’s kinda a problem in itself. Trace minerals (provided that they’re the right kind of minerals) are good for us, and there are some concerns that drinking nothing but pure distilled water over long periods of time can leach minerals from your body. Debatable how significant of an issue that is, but water with no minerals definitely tastes flat, so there’s that.
10 Likes
You might be able to recover a little bit of extra energy with a thermoelectric device, taking advantage of the heat being dumped by condensation. Ditto you might be able to make use of the salinity gradient between the dumped brine and the surrounding seawater. Obviously both of these things would produce far less energy than the sun that originally fell on the still, but it may let you recover a little bit of energy that would normally be lost, like regenerative braking does.
Actually, that makes me think that it would be interesting to have a heat-pump system. Basically, put heat into the water to make it evaporate, recover that heat to make it condense, and pump it back to the other side. The extra energy needed can then be covered by solar. Heat pumps (moving heat) in general gives you > 1 efficiencies compared with just turning energy directly into heat, so you’d need less energy total from the solar.
Doing a quick search, it looks like people are looking into this:
https://www.sciencedirect.com/science/article/pii/S0011916422005367
Coupling heat pump with single-effect evaporation desalination could produce 13 kg/s distilled water with energy consumption ranges between 10 and 13 kWh/m3 with price ranges from 0.0017 to 0.0023 $/L.
And https://www.sciencedirect.com/science/article/pii/S0011916401003411
Connection of a thermal desalination plant to a compression heat pump operating on steam
and water cycle increases by 2-3 times the economical and thermodynamic indicators of the desalination process. It allows for the substantial reduction of the cost of production of desalinated water.
(Plus a lot of other data. I have institutional access to articles if anyone wants.)
11 Likes
Well, my bs trigger is going off. One, “if the system is scaled up to the size of a small suitcase, it could produce about 4 to 6 liters of drinking water per hour.” One small suitcase sounds close enough to a square meter that I’ll run with that, but honestly none of my “small” suitcases are even half of that.
To evaporate one liter of energy of water takes 2300000 Joules. Solar energy maxes out at about 4968000 joules in one hour per square meter. That’s just a bit over 2 liters – and that’s assuming the sea water is at the boiling point and requires no additional heating to get evaporating. Now, sure, they may have economies of scale and energy recylcing, but the laws of thermodynamics suggest massive inflation on the part of their estimates. Where does the extra energy come from? Heat exchangers wouldn’t work – you’d just hit thermal equilibrium in a short while without some external power source. If you’re plugging it into the grid to provide air and water circulation, that needs to be accounted for and, of course, isn’t availble for much their target audience. If you’re using solar cells to generate power, you’re going to be much larger than a “small suitcase.”
7 Likes
I also wonder about the salt water. How close are the communities that are getting this salt water from the ocean? If they’re right next to the beach it’s no big deal, but for places further inland expecting them to lug liters of salt water, and then figuring out how to dispose of the left over brine seems like a logistical issue.
2 Likes
No worries, in (too) many areas the salt is coming to them 
:
9 Likes
I’m all for more cheap and efficient passive solar desalination, but the main “benefit” of this seems to be its small size conveniently sidestepping the question of large scal brine disposal, which is… well, a significant problem for any (filterless/evaporative) desalination solution. Sure, you could run a few of these in even a small area and the brine coming out of them wouldn’t be an issue, but for anything even village-scaled (and also assuming water usage that isn’t as massively wasteful as most Western countries) you’d still need a way of safely disposing of saturated salt brine without causing significant ecological harm.
4 Likes
Maybe it could be somehow included in existing processes, rather than slated for disposal:
4 Likes
Theoretically possible, but that would require reconfiguring the supply chain of an already existing industry towards a source that would in all likelihood be a lot more expensive. Possible? Yes. Likely? Not without government regulation.
2 Likes
Schauberger is pretty much out of fashion, these days. His work still informs turbine design and some other specific niches, but nobody wants to bring his name up because it attracts cultists in the same way that mentioning Tesla does.
7 Likes
Yes, 8 hours per day is extremely generous. One noteworthy extremely high-producing solar farm achieves the equivalent of nearly 7 hours per day, but it’s in a very dry desert in Arizona. Presumably, if you’re desalinating, you’re near the coast, where it tends to be cloudier.
In sunny urban parts of Australia, fixed-angle solar panels average annual output is roughly equivalent to 5 hours per day at full capacity. The limits are set by weather and sun angle.
Anywhere less sunny gets fewer “full capacity equivalent” hours per day.
So yep, lower your estimate between 12% and 37%, so roughly 8500 to 12000 litres.
Yes! The decarbonizing scenarios I’ve seen show that if everyone who could afford it went off-grid, the path to decarbonization electricity production would be a decade or so longer. Let’s not do that. The grid is worth keeping, because it’s the best way we have of distributing uneven generation and it’s already built, which is pretty damn handy.
5 Likes
I don’t think we need enough energy to actually boil water, do we?
I mean, water evaporates all the time from the oceans.
Caveat - I am not a scientist and I’m also a bit crap at sums.
4 Likes
From a brief skim of a search, I guessing that his (failed) vortex engine is claimed to be the heart of Nazi UFOs? Oh my!
2 Likes
2 Likes
Well, that’s the most efficient way. The cooler the water, the harder it is to get it to evaporate, but no matter how it evaporates, it takes the same amount of energy from somewhere. The ocean, to use your example, has a huge surface area for absorbing the sun’s energy as well as strong winds, a fractally large surface area what with all those waves, and yet the atmosphere only holds about 0.001% of the water of the ocean because the vast majority of it isn’t evaporating, even when it’s at the surface and being shone on with the full sun. The tiny portion that does evaporate sucks that energy out of the surrounding water, releasing it later when it forms clouds and rain.
If the oceans were boiling, no doubt part of the petrochemical industrial complex’s plan, the evaporation part would be happening much more efficiently – one of the reasons global warming is creating more powerful and frequent storms is that the slight increase in temperature is increasing the evaporation rate, which is (in a gross oversimplification) helping drive the weather severity increase.
Their device, at its heart, is still just a heat engine, only producing condensate instead of doing some sort of mechanical work. The laws of thermodynamics and thermal efficiency still apply.
5 Likes
I wonder how long it will take for potential improvements like this to be developed:
Maybe another energy source or hybrid solution would be a good alternative:
5 Likes
Honestly, the “5 hours full capacity per day” is NBD. I was very surprised when that turned out to be the case; I also thought we’d have to make solar more and more efficient / productive / etc before it took off.
It turns out that even with that limitation, PV solar is still the cheapest form of electricity ever made. That’s comparing final energy output, not nameplate. So even though you have to build about three or four times the peak power output to, say, coal or nuclear, solar is still cheaper to get the same energy output. As in “half the price” cheaper.
Yes! What we absolutely need is not cheaper or more productive solar, but energy sources that are uncorrelated with sunshine.
Wind is good - it tends to be stronger at night and on cloudy days.
Wave power is great in theory, and painful in practice - think of barnacles, seaweed, driftwood, plastic junk, along with the usual marine corrosion and rust. It’s really hard making things reliable when they have to live in the ocean for years and year.
Then you have storage - pumped hydro and batteries are the leading items right now. Lithium batteries are the established players, but Iron flow and Iron/Air batteries are looking interesting - they’d be bigger and heaver than lithium batteries, but also cheaper. So if you don’t need to move them (e.g. phone, car), using something other than lithium makes sense.
Whew. Sorry, this is my bread-and-butter work, and I get carried away with it. 
12 Likes
I like the concept of gravity batteries, where you use excess solar to raise ballast up a tower, then release as needed at night by using the descending ballast to spin a turbine.
2 Likes
Thanks for that explanation.
My only knowledge of primitive desalination or distillation comes from watching a very occasional survival show and the “All Is Lost” film (Redford). Effectively, this:
That they could scale that to six litres or so a day does seem remarkable.
4 Likes
Which works perfectly well for mechanical cuckoo clocks, but scales horribly.
Concrete density (what the weights are supposed to be made of) is just 2.4-2.8 times the density of water.
Any significant amount of energy storage based on gravity that is not pumped hydro easily becomes a mechanical and maintenance nightmare.
2 Likes
AFAIK no evaporative desalination relies on boiling, due to the high energy costs (unless your vessel is perfectly thermally insulated thermal losses to the ambient increase as temperature deltas increase, so energy needs for heating water increase exponentially with temperature rise, never mind the energy needed for the phase transition) and problems relating to boiling ever-more-concentrated salt brine. Lower temperature evaporation is simply far easier to deal with in all regards - especially when talking about something passively solar powered, as you then don’t need a massive parabolic reflector or similar energy concentration device.The point here isn’t approaching maximum theoretical water output for a given size of device, but maximum practical water output for a given size of device with a given (and highly restrictive) power source, materials cost, reliability needs, and so on.
3 Likes
