Simple, solar-powered water desalination (2020) • Hacker News Board

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

#81

Post by hoseja » Fri, Jul 02, 2021, 8:53 AM UTC

creshal wrote: post #57

vr46 wrote: post #38

This is the winning sentence for me: Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of.

Or is it? > 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. This is fine for a small scale demonstration unit, but with bigger plants you will again run into the problem of over-salinating seawater, destroying the environment (and reducing your still's efficiency)…

That would have to be a very small sea indeed.

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

#82

Post by londons_explore » Fri, Jul 02, 2021, 8:53 AM UTC

carl_dr wrote: post #61

tromp wrote: post #14

Earlier quoted context omitted.

The article says "per hour", not per day. Although that would seem able to support dozens of users rather than just 1.

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.).

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

#83

Post by Johnythree » Fri, Jul 02, 2021, 8:57 AM UTC

andromeduck wrote: post #33

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.

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.

You completely miss the point. Extracting fresh water from salt water creates brine and in a large scale plant it is extremely difficult to dilute it sufficiently.

The only answer is to pipe the brine into areas with strong currents, or dilute it by distributing it over a very large area.

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

#84

Post by ratsforhorses » Fri, Jul 02, 2021, 9:02 AM UTC

bjackman wrote: post #62

Does anyone know of any designs for DIY passive desalinators? My mum has a house on an island that doesn't have a natural source of fresh water (except rain of course), and it just occurred to me that a desalinator would be a fun thing to build there. Normally if there's a long drought she would have to have drinking water delivered by sea.

I'm sure you'll get better answers but I really liked the idea of ventilating greenhouses with salt water.... could be a good way to get the extra liquid needs..a quick google found me this https://www.sciencedirect.com/science/article/pii/S001191641...

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

#85

Post by Johnythree » Fri, Jul 02, 2021, 9:03 AM UTC

konschubert wrote: post #66

reizorc wrote: post #65

There's still the issue of what you do with all that salt

put it back into the ocean where it came from?

Brine is toxic unless it can be diluted. Which ends up being a huge problem in large plants.

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

#86

Post by Cthulhu_ » Fri, Jul 02, 2021, 9:04 AM UTC

bjackman wrote: post #62

Does anyone know of any designs for DIY passive desalinators? My mum has a house on an island that doesn't have a natural source of fresh water (except rain of course), and it just occurred to me that a desalinator would be a fun thing to build there. Normally if there's a long drought she would have to have drinking water delivered by sea.

The most simple ones ("survival" type, but it won't produce enough water unless you scale up) is spanning clear plastic over a pool of (shallow) salt water, weigh it down with a rock in the middle, and put a collector in the center underneath so the evaporated water runs down it.

But I'm sure there's commercial solutions out there.

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

#87

Post by ghshephard » Fri, Jul 02, 2021, 9:05 AM UTC

eterevsky wrote: post #12

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

Back of the envelope - say that you could get 7-8 hours of sunlight a day that could destill water. That would mean ~50 liters/day. ~20 Days to get 1m^3. Reverse Osmosis costs approx $0.50/m^3 water, so your payback on a $100 system would be ~200 * 20 Days or 4,000 Days to equal what you could get for spending $100 on buying water from a reverse osmosis system. The objective here isn't large scale economics, but self sufficiency.

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

#88

Post by c618b9b695c4 » Fri, Jul 02, 2021, 9:05 AM UTC

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?

It is my understanding that it is incredibly difficult to keep water pure. Transporting it any amount of distance from the source is likely to leech quite a few minerals from the available pipes.

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

#89

Post by Johnythree » Fri, Jul 02, 2021, 9:06 AM UTC

connorproctor wrote: post #28

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.

This doesn’t use electricity at all, the “solar power” is heat from the sun causing the water to evaporate. It’s a still, not a filter. According to the article the salt/brine freely flows back into the body of water.

Which by definition will increase the salinity in the local environment.

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

#90

Post by 867-5309 » Fri, Jul 02, 2021, 9:07 AM UTC

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 thought it would be something impressive like somehow using the obtained salt for further powering of the device but nope, another clickbait trip into bullshitland