alt Hacker NewsThere is a fundamental minimum amount of energy needed to desalinate: you can't take less energy to do it,than you could gain back (from osmotic pressure) if you allowed the desalinated water to expand a cylinder containing the residual brine. This is large. This paper is a thermal method, so it doesn't have an electricity input, but to justify their efficiency claim, they should really compare against what you could do by using the same surface area for solar panels, driving a conventional setup. My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.
This paper is interesting, however, in directly producing crystalline salt, which is lower volume than brine and easier to dispose of, maybe even valuable.
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Thermal methods require energy, it seems like this substrate is effective at maintaining its solar-thermal absorbing properties better than a material that will attract salts
> Testing their solar-thermal desalination technique using samples of water from the Pacific, Atlantic, and Indian Oceans, Guo and his team were able to make the surface self-cleaning. In other words, it extracted freshwater and directed the remaining salts to the passive region where they could be later collected without reducing the panel’s efficiency.
This is not "large" this is a moderate improvement. Albedo is likely only marginally affected, and the solar power input over area is the same.
Depending on this cost of this process it could very likely be a wash in terms of NPV
If this can be applied to mine effluent, you could replace the maybe with most certainly. Sulfuric acid effluent lakes leech all sorts of valuable metals out of the ground.
Focusing on pure energy efficiency might be missing the point of economic efficiency.
An RO desalination plant needs electric energy to drive the pumps, which might be generated by panels which are 15-20% efficient. So, if you can have cheap thermal desalination panels, they come out ahead even if 6x less energy eficient, you avoid the whole expensive and fragile desalination plant and you gain a low skill, distributed setup.
ScholarlyArticle: "Extreme salt-resisting multistage solar distillation with thermohaline convection" (2023) https://www.cell.com/joule/fulltext/S2542-4351(23)00360-4 .. https://scholar.google.com/scholar?cites=7551078272963689346...
"Desalination system could produce freshwater that is cheaper than tap water" (2023) https://www.eurekalert.org/news-releases/1002811
ScholarlyArticle: "Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer" (2022) https://www.nature.com/articles/s41467-022-28457-8
"Solar-powered system offers a route to inexpensive desalination" (2022) https://news.mit.edu/2022/solar-desalination-system-inexpens...
Brine is very easy to dispose of: you just pump it back to where it came from. Solid crystalline salt, on the other hand, is a hassle.
> My (limited) understanding is that conventional reverse osmosis is not far from the theoretical optimum, energy-wise, the main difficulties being operational (the membranes need declogging). And of course RO is more expensive than rain.
RO is about 2-4x the theoretical minimum, depending on how much water you're willing to reject.
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I always thought that if separating water and salt were easy, our bodies would have evolved to do it so that we'd be able to drink sea water and be fine. It must have been so expensive that searching for fresh water was worth it or there were plenty of fresh water that it was never a evolutionary pressure. Evolving kidneys capable of concentrating urine beyond 3 something percent concentration (sea water) perhaps required a massive restructuring of our internal organs and a huge constant energy expenditure, so we kept seeking fresh water.
ps. I have no clue what I'm talking about