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Simple, solar-powered water desalination

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Re: Simple, solar-powered water desalination

#141

Earlier quoted context omitted.

It comes out to about 0.4 liters per square foot, for those of you who are confused.

That means for every square rod of surface area, this unit produces over 11,000 hogsheads of water! Impressive.

To fit my Excel model, I really need to know how many barn-megaparsecs of water this produces per square smoot.

https://en.wikipedia.org/wiki/Smoot

https://www.google.com/search?q=barn%20megaparsec&oq=barn%20...

Re: Simple, solar-powered water desalination

#142
post #31

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…

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

very similar in principle to 10 years younger https://en.wikipedia.org/wiki/Pressure_wave_supercharger

Re: Simple, solar-powered water desalination

#143

Earlier quoted context omitted.

EDITED: bathtub ≈ 302 liters football field = 5351 square meters They achieved 5.78 L/m^2/h So 5351 m^2/football field * 5.78 L/m^2/h = 30928.78 L/h/football field 30928.78 L/h/football field / 302 L/bathtub = 102.4 bathtubs/football field/hour h/t to brudgers for the correction about football field surface area!

A football field is 5351m^2. Futbol pitches vary.

The Canadian Football League would like a word with you.

Re: Simple, solar-powered water desalination

#144

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…

Not so fast.

From the panel to the outlet, you only get out from 10 to 15% of input solar power, while thermal desal can use nearly all of it right away, and it leaves more concentrated brine. Multiple effect desal will probably move the efficiency up a bit. It's nowhere near clear cut.

Also if you have low potential reject heat from power plants, it's idea for desal use.

If you have nuclear as your heat source, then economy-wise thermal desal will beat electric many times over.

I recently read about thermochemical, and electrochmical desalination methods which can be added atop a thermal plant, further increasing thermal desalination efficiency.

Re: Simple, solar-powered water desalination

#145
post #96

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.

Just make a water tower to store provide pressure at night.

Re: Simple, solar-powered water desalination

#146

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 comp…

You can make a solar still without desiccants. Dig a hole somewhere that will get sunlight most of the time, drop a cup in the bottom to catch water, and create a funnel with a plastic sheet. (If you don't have a plastic sheet, branches can work.) There are various ways to optimize it, but a single water trap isn't going to keep a person alive.

Re: Simple, solar-powered water desalination

#148

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…

You seem to know a bit about this: would you have a similar comparison on the capital cost issues, e.g., cost per cubic meter for the at-scale version vs. this local small scale? I mean, that's probably unimportant even if there's a big difference given that remote locations simply wouldn't be practical to have a large plant. But if the costs are even only twice as much per cubic meter, the rapidity of rollout for the small-scale solution could provide rapid relief, especially in some of the areas of the world with acute shortages that need rapid remediation even if it's only a short term solution. (like Cape Town recently)

Re: Simple, solar-powered water desalination

#149
I have a stupid question (well, not to me because I don't know the answer): isn't desalination tech fundamentally similar to alcohol distillation? I know that's energy intensive too, I'm just curious, because I know a little about alcohol distillation and an wondering if the concepts are transferable.

Re: Simple, solar-powered water desalination

#150
post #87

Earlier quoted context omitted.

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

It is already - in the my opinion deeply silly book/movie series(?) Mortal Engines. I haven't read or watched them but saw a video ad and thought that it was the stupidest thing I had ever seen. Anyway it is effectively landships except they are massive steampunk mobile cities which grind up and harvest other sessile settlements and smaller mobile ones. I get the extended metaphor involved of colonalism and enrichmen…

The books are much better than the movie, but it's not exactly hard sci-fi. They predate the big surge in apocalyptic YA and are much better than they deserve to be. They're not less plausible than "Cities in Flight" or "Marooned in Real-time" or anything with warp drives and laser pistols.
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