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Simple, solar-powered water desalination (2020)

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

#61

Post by carl_dr »

tromp wrote: post #14
carl_dr wrote: post #2

This device "could" produce 1.5 gallons per day, per square metre of solar collecting area. The researchers estimate a system suitable for a family might be built for $100, so double or triple that after profits etc. I assume that the 1.5 gallons was the highest yield they would have had from a single day, had they had a 1 square metre solar panel, and the expected average yield would be less (accounting for cloud co…

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 (≈3.2 L),49 100 TMSS devices can be placed into a 10 × 10 array, filling an 1 m2 area, which would provide approximately 10–20 L of clean water every day depending on the weather condition."

The lower bound of 10l is outdoor performance on a partly sunny day. So I think they are just being conservative by saying it would meet the requirements of one person - coastal areas are frequently cloudy, and in some locations, there might be little sun for extended periods of time.]

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

#62

Post by bjackman »

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.

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

#63

Post by _0ffh »

sdoering wrote: post #32
im__so__meta wrote: post #24

Earlier quoted context omitted.

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.

Hmmm, yes it is. It's nearly too impressive!

From the article "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.", which sounds very different.

On this Q&A page [1] Zhang is quoted "Our current strategy, for example, is to use an assembly of 100 of these devices to achieve an area of 1 m2, which will increase the total production by 100 times to create 10-20 liters of clean water per day."

I don't want to sound too negative, but something doesn't add up here. Still, enough water for one person per square meter of desalination plant is an impressive result I think. The oceans are big.

[1] https://www.techbriefs.com/component/content/article/tb/feat...

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

#64

Post by Ice_cream_suit »

" Using a low-cost and free-of-salt accumulation TMSS architecture, we experimentally demonstrated a record-high solar-to-vapor conversion efficiency of 385% with a production rate of 5.78 L m−2 h−1 under one-sun illumination, where more than 75% of the total production was collected through condensation. "

Abstract is available here:

https://pubs.rsc.org/en/content/articlelanding/2020/ee/c9ee0...

The original journal article is available here as a pdf:

https://pubs.rsc.org/en/content/articlepdf/2020/ee/c9ee04122...

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

#67

Post by jeroenhd »

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…

> In production, they think a system built to serve the needs of a family might be built for around $100.

I think this is much more important to a great many people than the theoretical efficiency of reverse osmosis. Percentages greater than 100% always do well in media reports about these topics, but they're not necessarily the point of the exercise. If the goal was to produce a system that's as efficient as possible, the researchers wouldn't have used household-style supplies but more expensive, advanced materials.

Reverse osmosis is great for a central area such as a large city in a place with reliable distribution, but in many places around the world, an independent, affordable system that can turn seawater into drinking water for a family or two has much more value.

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

#69

Post by TeMPOraL »

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…

That's a good point, but! I wonder if it couldn't be more efficient overall, if you look at it globally. Is an equivalent reverse osmosis installation cheaper or more expensive to produce, in terms of embodied energy that goes into manufacturing and maintaining all equipment, including control equipment?

Also, I wonder which system would be easier to slap together in a garage out of leftover junk. Not everyone can rely on access to commercial-grade, turn-key solutions to a problem. A design that could be reasonably DYIed could be better in certain contexts, even if less efficient.

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

#70

Post by gregoriol »

bigbizisverywyz wrote: post #56

"Tests on an MIT building rooftop showed that a simple proof-of-concept desalination device could produce..." So doesn't look like they've even hooked it up to the sea yet, so still a bit to go for a real implementation, but still sounds interesting. I harbour a small dream that I could buy some seaside land someday on a Greek island and hook one of these desalination devices up to the sea and build myself a small oa…

The device itself would not be "on" the sea, it would just get water from it with a pipe/pump. I don't really see any reason it wouldn't work the same way by the sea: the main problem seems to be how to remove the salt, efficiently, not how to get water into the device, which is easier. Getting enough sun might even be harder than getting sea water.
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