[HN Gopher] Superefficient solar desalination (2020)
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Superefficient solar desalination (2020)
Author : abrax3141
Score : 59 points
Date : 2022-08-23 04:41 UTC (2 days ago)
(HTM) web link (cen.acs.org)
(TXT) w3m dump (cen.acs.org)
| itronitron wrote:
| Wow, they'll have enough salt to last forever.
| ncmncm wrote:
| This 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 wrote:
| > 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.
| labrador wrote:
| It'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 wrote:
| As 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.
| alx__ wrote:
| Hope 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
| bolangi wrote:
| > 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 wrote:
| > 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 wrote:
| Why 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.
| sacred_numbers wrote:
| This 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.
| abrax3141 wrote:
| What's the capital/op cost of r.o.? Isn't it just a pump and
| a membrane?
| abrax3141 wrote:
| Just for clarity, is that a 10x10cm solar panel?
| sacred_numbers wrote:
| What I mean is that a solar panel of any given size will
| produce electricity that can be used to desalinate an order
| of magnitude more water than a device like this of the same
| size. The device in this article desalinated 5.8 liters per
| square meter per hour in full sun, which means this 10x10cm
| device actually desalinated 58ml of water in an hour. A
| 10x10cm solar panel would produce enough electricity in an
| hour in full sun to desalinate approximately 600ml of water
| using reverse osmosis. A solar panel that was 1 square
| meter would generate enough electricity to desalinate about
| 60 liters of water in an hour in full sun.
| teknopaul wrote:
| I 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.
| beambot wrote:
| The linked article's production rate is off by two orders of
| magnitude. If you read the actual paper [1], the quoted
| production is 5.8L/hr/m^2 -- i.e. 5.8L/hr would require a 1 m^2
| system, not the 10cm x 10cm system under test (0.01m^2).
|
| https://sci-hub.se/10.1039/C9EE04122B
| beambot wrote:
| This device is literally some 3D printed nylon frames with
| papertowels!
|
| 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 wrote:
| There's also an aerogel layer. That's probably what would keep
| most people from building it at home.
| beambot wrote:
| They'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?
| abrax3141 wrote:
| What's the aerogel doing anyway? And I'd that something that
| can be bought? How expensive is it?
| CapitalistCartr wrote:
| Painfully expensive.
| abakker wrote:
| (2020)
| dang wrote:
| Added. Thanks!
| momeunier wrote:
| There is a Finnish company doing something like that.
| https://solarwatersolutions.fi/en/
| mota7 wrote:
| This 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]
| tuatoru wrote:
| Just 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 wrote:
| Minimum 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).
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