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Simple, solar-powered water desalination (2020)

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Re: Simple, solar-powered water desalination (2020)

#91

Post by ghshephard »

Johnythree wrote: post #79
shoto_io wrote: post #8

Earlier quoted context omitted.

Reading the article might help: > Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers.

Your rely is not helpful. The problem with any desalination system is that it creates brine. And brine in large amounts is toxic to the marine environment. The only difference with this example is its small scale. Once it is scaled up it will have the same problem as any existing desalinating plant.

But you would never scale this system up - it's entirely inefficient compared to reverse osmosis, on a cost basis. This is the type of system that you would use for just a few people, and as such - brine would never be an issue.

Re: Simple, solar-powered water desalination (2020)

#92

Post by Johnythree »

hnhg wrote: post #7
sonicggg wrote: post #6

What's the point here? Is electricity even the bottleneck of water desalination? I thought the biggest issue with these plans is the brine. That is the major pollutant, and no amount of solar panels will solve that.

The article directly addresses your point.

It doesn't. Any salt extraction creates brine which must be disposed of somehow.

Re: Simple, solar-powered water desalination (2020)

#93

Post by londons_explore »

femto wrote: post #48
eterevsky wrote: post #12

> 1.5 gallons of fresh drinking water per hour for every square meter 7 litres per m^2 per hour.

A comparison with reverse osmosis: 2.46kWh/m^3 (energy consumed per unit of water produced) is claimed for reverse osmisis [1]. This equates to 8.86MJ/m^3. Output for this still is 7L/(m^2.h) Assume a solar flux of 1kW/m^2. Energy consumed per unit of water is 1kW/m^2 / [7L/(m^2.h)] = 3.6MJ/0.007m^3 = 514MJ/m^3. Assuming the above is correct (check anyone?), the still uses 58 times more energy than reverse osmosis. T…

The MIT system appears to output clean water from each 'stage' of the system at variable temperatures. Thats energy lost - if a counterflow heat exchanger could be devised such that the output water was all cool, the final efficiency would be much higher.

They also don't seem to keep good control of salinity within the stages - I suspect after a few hours operation the efficiency will drop as the salinity gets higher and higher within the paper towels.

Re: Simple, solar-powered water desalination (2020)

#94

Post by jokoon »

einpoklum wrote: post #80

> The system delivered pure water That's toxic! We can't drink pure water. You have to maintain _some_ of the minerals in there, you just want to take most of the NaCL out. Does the system avoid this over-distillation? i.e. is the water properly potable, or is it just not-salty?

Just add some artificial minerals, it can come in some powder form I guess.

Re: Simple, solar-powered water desalination (2020)

#97

Post by Cthulhu_ »

FartyMcFarter wrote: post #71
spockz wrote: post #36

Earlier quoted context omitted.

Yes. So it is not an issue for the device. However, the salt does end up back in the ocean where at scale the salt levels will be higher leading to the (edit: local) environmental issues mentioned by the GP.

The sea is a big place. I could imagine perhaps some very localised effects near the plant, but even this isn't obvious.

> imagine > perhaps > but even this isn't obvious

So basically you're admitting you don't know anything about the subject, but you're making a conclusion anyway. It's OK to admit you don't know enough about a subject, and it's OK to not comment or theorize based on no knowledge besides an imagination.

Re: Simple, solar-powered water desalination (2020)

#98

Post by ComodoHacker »

crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

It's an example of a good old scientifically flavored clickbait.

The energy efficiency of anything cannot exceed 100% (until I missed something groundbreaking in physics).

Re: Simple, solar-powered water desalination (2020)

#99

Post by celticninja »

londons_explore wrote: post #82
carl_dr wrote: post #61

Earlier quoted context omitted.

Thanks for spotting that. I'm a little confused then, later in the article it says "The team estimates that a system with a roughly 1-square-meter solar collecting area could meet the daily drinking water needs of one person." So something doesn't add up. [Edit: the paper is available at https://pubs.rsc.org/en/content/articlehtml/2020/ee/c9ee0412... . It says, "To meet the average daily water intake for one adult (≈…

'drinking water' often doesn't mean the water a human literally drinks, but all the clean water necessary for living everyday life (bathing, flushing toilets, washing dishes, cleaning clothes, cooking etc.).

I am pretty sure if you had to get your water from one of these devices you would not be using it to flush toilets or other non-essential use.

And actually it does seem like 'drinking water' is actually drinking water and not for all those other uses you mentioned. As 3.7 litres is the amount required for a human male each day.

https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...

Re: Simple, solar-powered water desalination (2020)

#100

Post by 6nf »

einpoklum wrote: post #80

> The system delivered pure water That's toxic! We can't drink pure water. You have to maintain _some_ of the minerals in there, you just want to take most of the NaCL out. Does the system avoid this over-distillation? i.e. is the water properly potable, or is it just not-salty?

I drink distilled water all the time, it's not toxic in normal quantities.
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