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Simple, solar-powered water desalination (2020)

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

#31

Post by readflaggedcomm »

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 quantifies the heat re-used between stages. In the supplement, they note 600% is the maximum. The derivation is at the bottom of p834 from the journal pdf.

It's basically vapor produced at the measured average temperature divided by energy input.

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

#32

Post by sdoering »

im__so__meta wrote: post #24
eterevsky wrote: post #12

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

5.78 liters per square meter actually, per the article.

So in ideal conditions one could expect to provide about 12 to 15 people with drinking water per square meter. For me this is an impressive number.

If I calculate one unit with 300 dollars this would mean 5.5 cents per person per day for one year for fresh drinking water. And after that only a little bit for maintenance probably.

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

#33

Post by andromeduck »

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.

It makes no difference how concentrated the output brine is if it's the diluted to same concentration at the outlet and the same amount of fresh water is extracted.

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

#34

Post by goodcanadian »

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 outside to inside (or vice versa for air conditioning and refrigerators). In that case, it requires, for example, 1kW of electricity input to move 3.85kW of heat.

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

#36

Post by spockz »

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.

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.

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

#39

Post by theiasson »

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%.

The paper[0] goes into more detail about how the efficiency is calculated (scroll down a bit to see the actual formula).

[0] https://pubs.rsc.org/en/content/articlehtml/2020/ee/c9ee0412...

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