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Simple, solar-powered water desalination

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Re: Simple, solar-powered water desalination

#121

Post by corvuscorvid »

wffurr wrote: post #87
aSplash0fDerp wrote: post #81

The combination of hydrogen production and desalination using simple techniques are an exciting prospect for this decade. For architects of 21st century cities, most of these sustainable technologies would benefit from a cleanslate design, rather than trying to compete with builtup 20th century infrastructure. I think Austrailia is postured to be the biggest beneficiary of all of these "leaps" in technology this cent…

Landships sound like the plot of some dystopian future film; ecosteaders fight off the scavenger bands.

isn't this essentially a 21st century castle?

Re: Simple, solar-powered water desalination

#122

Post by onceUponADime »

steamer25 wrote: post #61
pfdietz wrote: post #31

Earlier quoted context omitted.

One fascinating (well, to me) component of modern RO desalination systems is the rotary pressure exchanger. Such a simple device, but so important. It looks like something from the 19th century, but the base patent was issued in 1988. https://en.wikipedia.org/wiki/Pressure_exchanger

I found this video which seems to animate the concept nicely: https://www.youtube.com/watch?v=udffed4Pq3g

Thank you, that was fascinating.

Re: Simple, solar-powered water desalination

#123

Post by thombat »

benevol wrote: post #77
sacred_numbers wrote: post #26

Efficiency in desalination is measured by comparing the energy expenditure to the enthalpy of vaporization of water (basically the energy required to distill water by boiling it). The current state of the art reverse osmosis desalination plants use about 3.2 KWh of electricity per cubic meter of fresh water ( https://pdfs.semanticscholar.org/d4d7/821d585699719289dddd10... ). This technology uses about 173 KWh of sola…

> For large-scale desalination, however, it is almost certainly more cost-effective to use solar panels, batteries, and large scale reverse osmosis systems. For large scale desalination, you need to attach tiny magnetic particles (think nano-scale) to the salt, and then extract it with magnets. And as a byproduct, you'll get Lithium.

For a sodium ion in solution it's more a question of pico-scale. And since most sodium salts are quite soluble you'll need some pretty exotic glue to attach that nano-magnetite.

Re: Simple, solar-powered water desalination

#124

Post by mark-r »

jfengel wrote: post #118
logfromblammo wrote: post #75

Earlier quoted context omitted.

Given the increasing popularity of 500 mL and 1 L units of bottled water, and the ubiquity of the 2 L HDPE beverage bottle, I think it would have been safe to measure the potable water output in liters. About the only things still sold by whole gallons any more are milk, water, iced tea, and lemonade, in the 1 gal jugs, or water in the 5-gal water-cooler jugs. I'm more confused by the efficiency numbers exceeding 100…

Servings of beverages in the US are still mostly in imperial measures. A can of soda is 12 ounces; so are most bottles. Beer in restaurants is usually a pint; if not, they'll specify ounces. A Starbucks venti is so called because it's 20 ounces; a tall is defined as 12 ounces. And American recipes still use cups and tablespoons (where the rest of the world has gone almost exclusively to grams, and not volume at all).…

Alcoholic beverages sold in containers are almost exclusively in metric. The old standard size was a fifth of a gallon, or 757 ml. When going metric this was reduced to 750 ml which is close enough that nobody would notice. Since it was ever so slightly smaller there was no pushback from the producers. https://en.wikipedia.org/wiki/Fifth_(unit)

Bottled water is often in metric too, even for single serving sizes.

Re: Simple, solar-powered water desalination

#125

Post by onceUponADime »

sacred_numbers wrote: post #26

Efficiency in desalination is measured by comparing the energy expenditure to the enthalpy of vaporization of water (basically the energy required to distill water by boiling it). The current state of the art reverse osmosis desalination plants use about 3.2 KWh of electricity per cubic meter of fresh water ( https://pdfs.semanticscholar.org/d4d7/821d585699719289dddd10... ). This technology uses about 173 KWh of sola…

Regarding remote locations- they usually lack water altogether.

A long time ago, as a kid i read about a experiment in a GEO-magazine harvesting water directly from air. The used idea was a hygroscopic chemical (Silicagel) collects the moisture from the air. Sunlight heats the silica gel- which releases the moisture as steam- which then condenses in a destil. It was very little water for a lot of effort, but the complete lack of moving parts and self-containedness of such a system deeply impressed me, being young and with Frank Herberts Dune on my mind.

To drop such a contraption into the deep dessert, where it could keep a plant alive, become a oasis with no basis ..

Re: Simple, solar-powered water desalination

#126

Post by adamcharnock »

DenisM wrote: post #96
pytester wrote: post #89

Earlier quoted context omitted.

>more cost-effective to use solar panels, batteries, and large scale reverse osmosis systems I can't imagine why you'd use batteries at all. Storing fresh water efficiently is cheap, storing power efficiently is not.

To make twice as much water you may need to either install a set of batteries to run at night, or install twice as much RO hardware to run during the day. Whichever's cheaper.

I made a comment with regards to this a while ago [1]. I'll repeat it here as I think it is relevant:

---

I’ve heard on the grapevine that facilities are now being designed which work at under 100% capacity in order to soak up excess/cheap power.

I believe this is coming about because: 1) the high cost of power and presence of sporadically cheap power makes it economically viable, and 2) designing equipment with lower duty cycles can actually provide substantial cost savings. Ie a facility which only runs 50% of the time is much cheaper to build & run than once which runs 100% of the time.

Sorry I cannot cite sources right now.

[1]: https://news.ycombinator.com/item?id=18929542

Re: Simple, solar-powered water desalination

#128

Post by AnimalMuppet »

gpm wrote: post #74
sacred_numbers wrote: post #26

Efficiency in desalination is measured by comparing the energy expenditure to the enthalpy of vaporization of water (basically the energy required to distill water by boiling it). The current state of the art reverse osmosis desalination plants use about 3.2 KWh of electricity per cubic meter of fresh water ( https://pdfs.semanticscholar.org/d4d7/821d585699719289dddd10... ). This technology uses about 173 KWh of sola…

Say solar panels cost $2 per watt, 6 liters/hour is about 20 watts of power, is about 40 dollars of solar panels. Plus whatever the reverse osmosis equipment costs. This system gets approximately 6 liters/hour/sq m... so it makes sense if we can manufacturer it for less than 40 dollars per square meter and space is cheap.

And, in places without usable water, space tends to be cheap.

Re: Simple, solar-powered water desalination

#129

Post by kragen »

newnewpdro wrote: post #113
kragen wrote: post #53

Earlier quoted context omitted.

You don't need batteries to run a reverse osmosis desalinator from solar panels; you can run the desalinator when the sun is shining and store the water. I'm surprised boats are already moving to lithium. I wonder if it would be worthwhile to tow the batteries in a separate buoy behind the boat?

> I'm surprised boats are already moving to lithium. When the alternative is a bank of lead-acid batteries with effectively ~50% usable capacity and poor charge efficiency, at least for cruisers effectively living at sea off solar power, it's not surprising at all.

The lead-acid batteries still cost a lot less per joule of capacity than the lithium batteries do. They just weigh more. Or maybe charge efficiency is the reason?

Re: Simple, solar-powered water desalination

#130

Post by kragen »

jefftk wrote: post #106
kragen wrote: post #42

This is a well-known approach known as multistage flash distillation: https://en.wikipedia.org/wiki/Multistage_flash_distillation It's surprising they didn't mention this in the article. (It is, of course, mentioned in the paper, because its authors are decent and honest people.) > more than 1.5 gallons of fresh drinking water per hour I don't understand. Are those imperial gallons, US gallons, US dry gallons, or Iri…

> I don't understand. Are those imperial gallons, US gallons, US dry gallons, or Irish gallons, which are all different sizes? Imperial and US gallons would both make sense, and you're right it's ambiguous. Dry gallons would not make sense, since this is a liquid quantity, and Irish gallons are long obsolete.

> Irish gallons are long obsolete.

The word "Irish" in this sentence is unnecessary. Gallons are long obsolete.

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