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Simple, solar-powered water desalination (2020)

news.mit.edu

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

#71

Post by FartyMcFarter »

spockz wrote: post #36
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.

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.

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

#72

Post by dmos62 »

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%.

I think of it as taking the combustible fuel energy required for a car's motor to drive it somewhere, divided by the energy required to turn the ignition key and press the pedal.

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

#73

Post by ppf »

eigart wrote: post #21
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%.

My understanding: As the water condenses onto the next surface layer in the stack, the solar heat is recycled. This is because the transition from gas to liquid releases heat. Really clever stuff! Edit: mixed up evaporate/condense

For that to work, each successive layer will need to remain cool enough for water to condense on it.

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

#74

Post by dsign »

This reminds me of how many places we have on the planet which are beautiful but inhospitable. Fixing the inhospitable part will come its own environmental impact, and the places will end up being less "beautiful". I vote we go to live elsewhere and leave the planet as a giant touristic resort :) .

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

#75

Post by kwhitefoot »

goodcanadian wrote: post #34
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%.

Usually, numbers over 100% mean that you are putting in less energy than is needed for the process. In this case, that would mean putting in a little over a quarter of the needed energy. That does not imply free energy or anything. The rest of the energy has to come from the environment. A heat pump is another common example with efficiency numbers in the same ballpark. With a heat pump, the heat is being moved from…

Efficiency is still the wrong name. What you are describing is usually referred to a coefficient of performance, abbreviated to COP.

See https://en.wikipedia.org/wiki/Coefficient_of_performance

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

#76

Post by raxxorrax »

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%.

Exposing a deep body of water to sunlight is probably the reference.

edit: deep as in practically having unlimited heat capacity and the heat conductivity of water.

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

#77

Post by ppf »

It's incredibly disappointing to see MIT put its name to some apparently PhD-level research that claims over-unity efficiency, and apparently (according to the picture) using a few baking trays and tinfoil.

It also does not explain how to deal with the increased salination of the water source, nor how water can continue to condense on the successive layers of the device as they are heated due to that condensation.

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

#78

Post by wesleywt »

defend wrote: post #29
azinman2 wrote: post #22

Earlier quoted context omitted.

Yes. Why wouldn’t you?

A healthy exercise in skepticism.

An exercise in skepticism is actually asking a specific question that bothers you about the article. And not just a random "I don't believe this".

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

#79

Post by Johnythree »

shoto_io wrote: post #8
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.

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.

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

#80

Post by einpoklum »

> 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?

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