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Does anyone working in the field know if a 100-1000x reduction in energy consumption of desalination is theoretically possible - using so called promised superm

Does anyone working in the field know if a 100-1000x reduction in energy consumption of desalination is theoretically possible - using so called promised supermaterials based on graphene/nanotubes etc. or some kind of economies of scale ? Or are we limited by the law of physics here ? I am really skeptical of promise of materials like graphene because although i have heard about magical properties for so many years now i have never heard of practical mass manufacturing completely upending an old school method for something. May be i am not knowledgeable enough. This is one of the technologies that is increasingly important for the future of the earth especially in water poor countries with heavy population. In the large scheme of things it might turn out cheaper to move population closer to the coasts, have desalination plants instead of other solutions to water scarcity assuming renewable energy costs reduce significantly as well along with a lot of surplus.

flavius29663 8y ago
Water evaporated and leaves brine behind, at any temperature above 0C (even below through sublimation). Theoretically I guess you can imagine the sun evaporating the water that you capture, so you could have close to 0 energy input. So there is no physical limit I suppose. But you don't want to wait for the sun, you want to speed up that process, I don't know what the limit is there, when the speed matters (how much does it matter?).
- knicholes 8y ago
  Maybe with enough surface area, waiting for the Sun wouldn't be such a time-consuming task.
  - mjevans 8y ago
    Any site doing this is more likely to use a mirror array for concentration, but I'm not sure offhand which shape(s) might be optimal for different reasons.
jartelt 8y ago
Anything close to a 100-1000x reduction in energy consumption is unlikely in the next 10-20 years. That said filters have steadily gotten better over the years (better throughput, more durable, etc.) Also, the main thing to focus on is cost of water produced. If you design a new filter that is much more energy efficient but costs 100x more than the standard plastic filter, it may not provide much advantage.
zozbot123 8y ago
There is a theoretical minimum energy required to desalinate water, because an entropy cost is involved. At room temperature, the cost works out to about 0.8 kWh per cubic meter, and our best systems seem to reach approx. 25% efficiency.
- solarkraft 8y ago
  Thanks. It's quite a bit better than I expected.
brrt 8y ago
The current state of the art (reverse osmosis) is already fairly good. The first link I found [1] demonstrates the increase in efficiency - we're talking about roughly 3 kWh/m3. I don't recall exactly, but I think that is in an order of 5 of the theoretic maximum. At an average, rather immodest level of water consumption per capita (~1580 m3/annum), then this is about ~4740kWh per year, or 13 kWh per day. I'd say this is significant, but then: For comparison, current energy use per capita in the USA is 7000kg-oil-equivalent [2] (or 81000 kWh [3]), so an additional 4740 kWh is about 5%. The real problem is that people use absolutely indecent amounts of energy and water and other resources, usually for no good reason at all... [1] https://s3.amazonaws.com/academia.edu.documents/45145253/The_Future_of_Seawater_Desalination_Ener20160427-32244-1lwtahi.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1547574667&Signature=weT9blJw2YOThFa7WK1uTsgwZyw%3D&response-content-disposition=inline%3B%20filename%3DThe_future_of_seawater_desalination_Ener.pdf https://s3.amazonaws.com/academia.edu.documents/45145253/The... [2] https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locations=US https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locat... [3] https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent
- rconti 8y ago
  Thanks for the stats -- I actually just installed a solar array on my house which should produce around 8000kWh/yr which is in the ballpark of how much energy our 2-person household would need to desalinate our own water, so it's nice to have a tangible metric (and to know it could be done on our own roof space)... ~$24k installed, does not include cost of desalination plant :D
  - deleted 8y ago
    [deleted]
- buzzdenver 8y ago
  Are those numbers right? 1580 m3/year is 4.3 m3 or 1100 gallons per day. http://www.theworldcounts.com/stories/average-daily-water-usage http://www.theworldcounts.com/stories/average-daily-water-us... says 100 to 175 gallons per day per person.

flavius29663 8y ago

Water evaporated and leaves brine behind, at any temperature above 0C (even below through sublimation). Theoretically I guess you can imagine the sun evaporating the water that you capture, so you could have close to 0 energy input. So there is no physical limit I suppose. But you don't want to wait for the sun, you want to speed up that process, I don't know what the limit is there, when the speed matters (how much does it matter?).

knicholes 8y ago
Maybe with enough surface area, waiting for the Sun wouldn't be such a time-consuming task.
- mjevans 8y ago
  Any site doing this is more likely to use a mirror array for concentration, but I'm not sure offhand which shape(s) might be optimal for different reasons.

jartelt 8y ago

Anything close to a 100-1000x reduction in energy consumption is unlikely in the next 10-20 years. That said filters have steadily gotten better over the years (better throughput, more durable, etc.) Also, the main thing to focus on is cost of water produced. If you design a new filter that is much more energy efficient but costs 100x more than the standard plastic filter, it may not provide much advantage.

zozbot123 8y ago

There is a theoretical minimum energy required to desalinate water, because an entropy cost is involved. At room temperature, the cost works out to about 0.8 kWh per cubic meter, and our best systems seem to reach approx. 25% efficiency.

solarkraft 8y ago
Thanks. It's quite a bit better than I expected.

brrt 8y ago

The current state of the art (reverse osmosis) is already fairly good. The first link I found [1] demonstrates the increase in efficiency - we're talking about roughly 3 kWh/m3. I don't recall exactly, but I think that is in an order of 5 of the theoretic maximum. At an average, rather immodest level of water consumption per capita (~1580 m3/annum), then this is about ~4740kWh per year, or 13 kWh per day. I'd say this is significant, but then: For comparison, current energy use per capita in the USA is 7000kg-oil-equivalent [2] (or 81000 kWh [3]), so an additional 4740 kWh is about 5%. The real problem is that people use absolutely indecent amounts of energy and water and other resources, usually for no good reason at all... [1] https://s3.amazonaws.com/academia.edu.documents/45145253/The_Future_of_Seawater_Desalination_Ener20160427-32244-1lwtahi.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1547574667&Signature=weT9blJw2YOThFa7WK1uTsgwZyw%3D&response-content-disposition=inline%3B%20filename%3DThe_future_of_seawater_desalination_Ener.pdf https://s3.amazonaws.com/academia.edu.documents/45145253/The... [2] https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locations=US https://data.worldbank.org/indicator/EG.USE.PCAP.KG.OE?locat... [3] https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent https://en.wikipedia.org/wiki/Tonne_of_oil_equivalent

rconti 8y ago
Thanks for the stats -- I actually just installed a solar array on my house which should produce around 8000kWh/yr which is in the ballpark of how much energy our 2-person household would need to desalinate our own water, so it's nice to have a tangible metric (and to know it could be done on our own roof space)... ~$24k installed, does not include cost of desalination plant :D
- deleted 8y ago
  [deleted]
buzzdenver 8y ago
Are those numbers right? 1580 m3/year is 4.3 m3 or 1100 gallons per day. http://www.theworldcounts.com/stories/average-daily-water-usage http://www.theworldcounts.com/stories/average-daily-water-us... says 100 to 175 gallons per day per person.