7 ms·
Superefficient solar desalination (2020)
- abakker 4y ago(2020)
- dang 4y agoAdded. Thanks!
- ncmncm 4y agoThis is just as exciting as when it came up in 2020. One of the nice features of this system is that, overnight, the wick self-cleans, diffusing accumulated salt back to the sea water. Another way to recycle the heat of condensation, in a bigger system not relying on capillary action, would be to circulate incoming brine in the condenser on its way to the evaporator, pre-warming it while cooling the vapor; and run outgoing brine through a heat exchanger to further warm incoming brine. A key observation in design of low-cost desalination is that there is no need to minimize the amount of brine circulating in the system. So long as heat collected in the brine is not wasted, you are better off circulating more brine. The less you concentrate the brine, the easier it is to get water out.
- bertil 4y ago> diffusing accumulated salt back to the sea water. A big issue of desalinisation is the increase in salt in water: brine streams coming out of osmosis plants are dead zones in the sea. I'm not sure this is a good idea for the shore.
- ncmncm 4y agoAs I noted, there is no need to concentrate the brine to such a degree that discharging it could be a problem. But even if you did, discharging the brine through a long, leaky pipe or hose would avoid creating any dead zones.
- cma 4y agoHow do you create a long leaky pipe without bio-fouling clogging it up? I guess the high salinity itself could prevent fouling.
- ncmncm 4y agoWith positive pressure and small holes, it would be hard for bio to get in and foul it. Generally you are more worried about biofouling on water intakes, with good reason.
- labrador 4y agoIt's only seems like a big issue to people who don't know a lot about the ocean. I grew up surfing in a town at "sewer peak". The effluent from a sewage treatment plant was nearby. It was too close to shore, so they moved the discharge further out into deeper water. Discharging water with a higher salt content than the ocean wouldn't cause any harm at the discharge point, so this concern always seemed like a canard or unfounded theory to me. Some people don't want desal plants near them, so they throw this out there for NIMBY reasons.
- ncmncm 4y agoI gather San Diego discharged sewage into the sea forever. When they finally got to cleaning it up, maybe to appease surfers, they were forbidden because an ecosystem had grown up dependent on it the way it was.
- labrador 4y agoSanta Cruz didn't clean it up because of surfers, who didn't care because it wasn't very noticeable, although you knew you were taking a chance of getting mildly sick. It's really difficult to resist going out when the waves are good. It was because the fecal bacteria count was over the new environmental standards that came to be in the last two decades of the 1900's. Many people don't realize there's an acceptable amount of mouse dung and insect carcasses in the food they buy, so it may sound gross to surf in gray water, but it really wasn't. It may be a bigger problem in San Diego because the water is much warmer than the cold currents the come down the coast from Alaska to Santa Cruz (along with some good waves)
- hamlsandwich 4y ago> Discharging water with a higher salt content than the ocean wouldn't cause any harm at the discharge point Sewage and hot, concentrated brine are not the same. Plenty of studies show that there is harm to ecosystems, that's often not properly addressed. - https://www.ccc.tas.gov.au/wp-content/uploads/2018/11/Apx-22-Desalination-Plants-Uni-Sydney-Brine-Discharge-Marine-Env-Impact.pdf https://www.ccc.tas.gov.au/wp-content/uploads/2018/11/Apx-22... - https://phys.org/news/2019-01-brine-discharge-desalination-good-news.html https://phys.org/news/2019-01-brine-discharge-desalination-g...
- bolangi 4y ago> can produce 5.8 liters of fresh water per hour in full sun All this from a 10 x 10cm panel. Sounds too good to be true.
- LeifCarrotson 4y ago> On the roof, the device produced 72 mL of water in 4.5 hours. That sounds more in line with what I'd expect from Massachusetts sunshine.
- jeffbee 4y agoWhy does the article describe the difference between 5.8l/h and .072l/4.5h as 50% lower? It looks to me like this ratio is more than 300x.
- teknopaul 4y agoI wonder why seaside towns don't all have 1m2 of this per 1000 residents. Seems like a no brainer if it really works but I can't believe it does.
- sacred_numbers 4y agoThis is incorrect. The statistic of 5.8 liters per hour is actually liters per hour per square meter. A 10x10cm panel would produce 58ml per hour in full sun. If you instead put a solar panel with 20% efficiency and used the electricity for reverse osmosis you would produce about an order of magnitude more water per square meter. This may have lower capital or operational costs, though, and it is certainly more decentralized, so it could be useful in some situations.
- alx__ 4y agoHope plans for this will get released so that others can build their own. Would be great to use while sailing or doing costal hiking/camping
- beambot 4y agoThis device is literally some 3D printed nylon frames with papertowels! https://sci-hub.se/10.1039/C9EE04122B https://sci-hub.se/10.1039/C9EE04122B Given the simplicity and cheapness of the device... has anyone replicated their results? Seems like a fun weekend project!
- papercrane 4y agoThere's also an aerogel layer. That's probably what would keep most people from building it at home.
- beambot 4y agoThey're using aerogel for its transparency & thermal insulation properties. Are there any other good contenders that are easier to procure -- e.g. if you're shooting for practicality rather than record-setting?
- zbrozek 4y agoMulti-pane windows would probably be the easier homebrew option. You could even make the panes out of plastic film (e.g., ETFE).
- hamlsandwich 4y agoI had the same thought - an off the shelf double-paned window module would be great, otherwise a homebrewed version with two panes and a partial-vacuum pumped out between them.
- abrax3141 4y agoWhat’s the aerogel doing anyway? And I’d that something that can be bought? How expensive is it?
- CapitalistCartr 4y agoPainfully expensive.
- momeunier 4y agoThere is a Finnish company doing something like that. https://solarwatersolutions.fi/en/ https://solarwatersolutions.fi/en/
- itronitron 4y agoWow, they'll have enough salt to last forever.
- tuatoru 4y agoJust out of curiosity, does anyone know the theoretical minimum energy required for desalination? Is it the energy released when salt is dissolved in water? By analogy, Vaclav Smil says the best iron smelting and ammonia synthesis plants are within 100% of the theoretical minimum energy required for the chemical reactions to take place - within 50% in the case of the very best iron smelters. Aluminum smelting is slightly worse than these two IIRC.
- mota7 4y agoMinimum is around 1 kWh/m^3 for sea-water levels of salt concentration. (It varies a fair bit depending on salinity, the actual salts involved, the temperature etc etc).
- tuatoru 4y agoThank you!
- zeristor 4y agoDo you have a reference on Vaclav Smil? I’d be interested in reading the book that discusses this sort of thing.
- mota7 4y agoThis is surprisingly poor production? Peak insolation varies widely, but 1000W/m^2 is a typical value. 5.8L/hr/m^2 means that it's using something like 180kWh/m^3 on raw solar insolation. For comparison, reverse osmosis is around 3kWh/m^3. This means that 20% efficient solar panel would produce around 67 L/hr/m^2 (aka ~11x more). Obviously this is passive versus active, but it's still a surprisingly large difference.
- deleted 4y ago[deleted]
- johnbcoughlin 4y agoConverting water to steam is an extremely inefficient way to separate water from salt.
- someguydave 4y agoIf reverse osmosis desalination only takes 3 kwh/m^3 then you could produce 4 million acre-feet for 14.9 billion kWh which would cost about $1.5 billion per year. That is pocket change for replacing a big portion of Colorado river water. I guess Californian environmentalists love Hetch Hetchy reservoir and making the desert stay dry.
- sacred_numbers 4y agoReverse osmosis desalination does have some capital and operational costs, though, but you're not far off. 5 billion m^3 or 4 million acre-feet would still only be about 2.5 B per year. The problem is that if you fill up the Colorado River the farmers that own the water rights will just drain it down again because they don't pay based on the quantity they use. Or if they do pay based on quantity the price is much lower than the cost of desalination. Desalinating large quantities of water without fixing the water rights situation would be like minting pennies out of gold.
- someguydave 4y agosure, there would be capital costs but those could be financed, plenty of people would lend 30 year money for such an enterprise. So to be clear you hate agriculture so much you are willing to end it with drought? I like agriculture personally. I would like more of it! There is plenty of desert in the west that could be made to bloom.
- squarefoot 4y agoI wonder what they could do with all that salt, as releasing it in the environment isn't exactly safe. Would be there any uses for the huge quantities involved?
- zeristor 4y agoI posted this link to a BBC World Service podcast about a year ago of using a solar still in Somalia to produce water for a greenhouse AND salt: https://www.bbc.co.uk/programmes/w3cszv2l https://www.bbc.co.uk/programmes/w3cszv2l Just thought I’d mention it heat again. Different technology, but pointing out there is demand for the salt. Not to detract from this article which is amazing. The actual paper of which is here: https://pubs.rsc.org/en/content/articlelanding/2020/EE/C9EE04122B https://pubs.rsc.org/en/content/articlelanding/2020/EE/C9EE0...
- zeristor 4y agoSomeone, a YouTuber, has made a YouTube video about the work: https://youtu.be/bTa6QnNIzsQ https://youtu.be/bTa6QnNIzsQ