Crystalline nets harvest water from desert air, turn CO2 into liquid fuel | Hacker News Reader

Crystalline nets harvest water from desert air, turn CO2 into liquid fuel

sciencemag.org

379 pointssohkamyung130 comments

It's a cool idea and all, but how do the calculations look for actually moving enough air through the "net"?

One cubic meter of air at 100% humidity and 25C only holds 22g of water. For the 8 liters per day value it doesn't seem like an unreachable amount: 363 cubic meters of air need to pass through the filter. You probably need to more than double that number due to relative humidity not being at 100% and we probably won't get all the water in the air, but it seems reachable.

On the other hand, 22500 liters per day seems quite crazy. I'm interested to see how they're going to tackle this.

It's a cool idea and all

I see what you did there...

At 100% humidity and 20 C air holds 18 g H2O per cubic metre so to deliver 22 500 kg of water per day they must entirely dessicate 1.25e6 m3 of air. Air is about 4 kg per m3 so this means moving 5 000 tonne of air through the system.

If the energy cost of moving the air is equivalent to lifting it is, say, two metre then the energy required to do this is 5e6 * 9.8 * 2 joule, about 2e9 J or 555 kWh so it would need something like 250 m2 of solar panels at 20 5 efficiency for 10 hours.

At higher temperatures 100 % is more water but that only changes the yield by at most a factor of about three.

Of course the humidity in the areas where this would be used is much lower so the amount of air to be processed is correspondingly higher.

I'm not saying it can't work, or guaranteeing that I haven't slipped a decimal place somewhere but these figures suggest to me that it would be very expensive and might be outcompeted by piping in water from desalination plants.

1. If there is wind, obviously you need less energy to move the air through the device.

2. Second, your estimate based on gravity is off. Apparently, the fan power to move air is given by [1]

Power = (pressure change of air) x (volume/time of air)

Volume/air is 1.25e6/10hours = 1.25e5. Assuming that the pressure change through the device is minimal, we can look at the bottom most line (100 Pa) on the first figure, to estimate ideal power to be ~5KW of power. Even with loses, having 10-20 KW power systems is equivalent to the energy consumption of 2-5 large houses.

[1] https://www.engineeringtoolbox.com/fans-efficiency-power-con...

”Air is about 4 kg per m³”

https://en.wikipedia.org/wiki/Density_of_air gives around 1.3 kg/m³ for dry air. If you add the 18 grams of water you give, you only get around 1.32 kg/m³.

⇒ I think 4 kg/m³ is too high.

Humid air is actually less dense than dry air, as any aircraft pilot should be able to tell you. That's because the water molecule H2O has a molecular weight of 18, while O2 has a molecular weight of 32 and N2 has a molecular weight of 28.

Thanks. I misremembered that one.

So it reduces the energy cost by a factor of three. Still needs a heap of solar panels to get about 200 kWh per day. I have a friend in southern France who has eight panels and it has taken him fifteen weeks this summer (105 days) to get 1000 kWh this summer, say 10 kWh per day so you need 160 panels. to get 200 kWh per day.

My purpose was to point out that the size of the installation is likely to be quite a bit bigger than a cursory glance at the article would suggest.

555 kWh is about 55 USD at $0.10/kWh, so for 22.5 m3 that's about $2.5 per m3 (or 1000 l) of water, cheaper than EU residential prices (3 EUR per 1000l in France) and also than than what I can find about US residential prices (NYC: $10/100 cuft or $3.5/1000l) Cheaper is good, because this is just marginal electricity cost, total cost per 1000l is going to be higher, it will include maintenance and equipment depreciation.

They aren't using grid power, they are using solar so you need to consider the capital cost over the lifetime of the system.

And remember that my figures assume that you extract all of the water from 100% humidity. But you don't have that and anyway a condenser would work perfectly well if you did.

The assumption above is 100% humidity. Which you won't get even close to in a desert near Amman, where it's around 50%, and only because of the ocean proximity.

If you look at the humidity map, it's rather clear that most warm areas away from the ocean/sea are screwed - it's around 18% humidity.

https://www.windy.com/-Show-add-more-layers/overlays?rh,31.9...

Not to mention the energy you need to remove 14 MWh of energy from the water in order to condense 22,500 kg of it.

This is usually the more important part and the part most projects hide. 14MWh in 24h is about .5MW = 500,000W. For comparison a Pentium has to dissipate about 100W, so it's like 5000 Pentiums.

The Pentium has a big dissipator that is directly under a fan, that has another fan(s) nearby to get more fresh air. And the Pentium runs at ~50°C that is like 30°C(15°F) over the room temperature. I doubt this absorbed gets so hot, so the temperature difference is probably only a tenth of a degree, so the dissipator must be much bigger. (Dissipation is not linear in fluids, so a 1/30 of difference of temperature usually means more than a x30 bigger dissipator.)

A household air dehumidifier can pull 8 litres per day out of a 500 sqft home - seems possible.

https://www.directenergy.com/learning-center/energy-efficien...

Is that with all the windows closed?

That’s not in a desert though.

the link is about humidifiers, not dehumidifiers

https://blog.constellation.com/2018/09/21/energy-efficient-d... gives a ballpark number:

"In order to be approved by ENERGY STAR®️, energy-efficient dehumidifiers must have an energy factor of at least 2.00, or an energy factor greater than 2.80 for dehumidifiers that remove more than 75 pints of moisture a day."

So 2-3 litres water extracted per kWh electricity consumed (And I'm guessing this is probably in best case damp conditions).

There's plenty of people here who have done some fantastic math that throws red flags at this "I'm going to save the world" project. And each of you are beautiful people.

What gets to me, these overly complicated dehumidifiers keep popping up every 6 months and make a big buzz. And each time, "Look at this brand new thing that no one has ever thought to do!" That's the part driving me crazy. It's the same investment sham, over and over. Slightly different method, but the same idea "We tested a dehumidifier in a place with high humidity. We collected water. Throw money at us." I give it props for at least being done in Arizona. But Arizona has higher humidity than a lot of the other water problem areas in the world.

But I'm the asshole because I don't say "I'm curious how they're going to overcome the humidity problem."

No, they're not going to solve it. They're going to disappear. Why? Because they took the money and ran. Like the hundreds of other assholes who keep coming up with these middle school "I know how to save the world" ideas.

There's a sucker born every minute, and we've done almost nothing to change that. The economy in its current form would probably crash if all the suckers disappeared.

I feel the same way about blockchain healthcare startups. If you put PHI on a blockchain it will get distributed, and one day cracked and shared. Modern cryptography is not a silver bullet that will last forever as-is.

By then the founders (who we see these days on Techcrunch taking money for these sham projects) will be long gone.

Whe modern cryptography is cracked 50+ years from now I'm not really going to care about people having my medical info. I'll be dead anyway

>I give it props for at least being done in Arizona. But Arizona has higher humidity than a lot of the other water problem areas in the world.

It does? Have you ever lived there? I'm not sure about actual humidity number comparisons between there and other deserts, but during the summer it's so dry that whenever I spilled water on the floor, I didn't even bother cleaning it up, because it would evaporate in seconds while I was watching it. Seriously, if you're trying to test a device like this within the US, I don't know any lower-humidity place to go than the Sonoran Desert of Arizona.

First, it doesn't state Sonoran Desert. Just "In the desert of Arizona". That entire region of America is a desert if you grew up in places like Florida or the western part of the Pacific Northwest. Because this article already treats the idea of "pulling water out of air" as some brand new concept that's never been done before, I already assume they're not using the scientific definition of desert.

However, check out NOAA. Here's a chart of average relative humidity of cities throughout the US (https://www1.ncdc.noaa.gov/pub/data/ccd-data/relhum18.dat). From 1950 to 2018.But you'll notice in the Arizona cities, plenty times of the year, the average humidity is between 40%-60%.

Still, this is better than the Water Abundance X-Prize winner from Oct 2018. The article was on HN: https://www.fastcompany.com/90253718/a-device-that-can-pull-... These bastards "tested" it in Hawaii of all places.

So yes, I'll say I give them props for doing this in Arizona. But I'm not going to do backflips. There's still plenty of humidity in Arizona. Especially if you time your testing in the right time of year. But I mean, when huge investment money is on the line, no one would ever dare cheat or try to tip things in their favor unethically. Oh no. Never. That's just silly talk. No one has ever lied in experiments to make wheel barrows of money...cough Theranos cough.

Plus water evaporating from the ground isn't just based on lack of air humidity. It's also on heat of the ground. Just straight up steaming away. Same happens here in Florida, but you can't really confuse Florida with dry air.

>Plus water evaporating from the ground isn't just based on lack of air humidity. It's also on heat of the ground. Just straight up steaming away.

No, this was inside where it wasn't that hot, though we weren't running A/C.

Also, the humidity in the cities is usually higher than in the open desert because of all the (yard) irrigation, water features, canals, etc.

> Here's a chart of average relative humidity of cities throughout the US (https://www1.ncdc.noaa.gov/pub/data/ccd-data/relhum18.dat). From 1950 to 2018.But you'll notice in the Arizona cities, plenty times of the year, the average humidity is between 40%-60%.

I think you're reading that wrong. Doesn't M stand for "Max" and A for "Average"?

If so, the average in southern Arizona cities is 15%-30% and in northern Arizona cities 30%-50% (which matches my experience).

Tucson actually has a small monsoon season, which I am desperately waiting for to cool us off. It's an interesting weather pattern.

https://azclimate.asu.edu/monsoon/

Tucson gets a lot more rain than say, Death Valley.

> Last year, he formed a company called Water Harvesting that this fall plans to release a microwave-size device able to provide up to 8 liters per day. The company promises a scaled-up version next year that will produce 22,500 liters per day, enough to supply a small village. “We’re making water mobile,” Yaghi says. “It’s like taking a wired phone and making a wireless phone.”

Any ballpark estimates on the cost for a residential use unit? i.e. 200L-1000L/day

Also, is it feasible for this to markedly effect downstream areas?

i.e. If there's eastwardly wind flowing through Nevada where machines are extracting humidity at an extreme scale, how might the 30%+ humidity-requiring plants (i.e. that Jamaican Yerba) in Utah hold up?

water wars 2.0, version: air.

humidity credits & humidity sink surveillance with humidobfuscation 'consultants'.

>Also, is it feasible for this to markedly effect downstream areas?

> i.e. If there's eastwardly wind flowing through Nevada where machines are extracting humidity at an extreme scale, how might the 30%+ humidity-requiring plants (i.e. that Jamaican Yerba) in Utah hold up?

There is a LOT of water in the air, 12,900 km3 [0]. As a comparison, the US uses 1.2 km3 of water per day (all uses combined.)

[0] https://www.usgs.gov/special-topic/water-science-school/scie...

[1] https://www.usgs.gov/special-topic/water-science-school/scie...

Interestingly in that second link - the largest category of water usage is for thermoelectric power generation, actually using more than irrigation. I wouldn't have guessed that, and as we start to rely less on burning things for power, that number should come significantly down.

>and as we start to rely less on burning things for power, that number should come significantly down.

Nuclear plants also need cooling towers.

Also note that heat exchangers can also use seawater, though with higher maintenance costs from biofouling.

No, subs and aircraft carriers should be obvious counter examples. They just need cooling and large bodies of water can work just as well, however at scale this can harm local wildlife. https://nuclear.duke-energy.com/2013/11/13/why-don-t-all-nuc...

  the largest category of water usage is for thermoelectric power generation, actually using more than irrigation

Isn't there a lot of overlap there? Hydroelectric doesn't consume the water, it just takes energy from its gravity.

Thermoelectric sort of does consume it, I guess. They inject the water down into geysers to produce steam. My home town, Santa Rosa, California, gets most (all?) of its power from thermoelectric. https://en.wikipedia.org/wiki/The_Geysers

To be clear, when the article says "thermoelectric", they're talking about any power plant that heats up water to generate steam, which is to say, every coal, nuclear, and combined-cycle natural gas power plant in the country.

Ah...makes sense.

I don't think that's consumption, though? Steam is still water, just in gaseous form, and it becomes liquid again via condensation.

I was about to post the same objection, the steam used in the turbine is in a closed cycle for all that I know.

But a large amount of water is evaporated to cool the condenser in big plants that produce more waste heat than can be used by local low intensity heat consumers (district heating, greenhouses).

In any case, water consumption is an incredibly weak metric if it's not somehow normalized by source and sink impact. It's irresponsible alarmism when e.g. irrigation use from a plentiful source is measured on the same scale as consumption of a non-replenishing mineral occurrence and/or water use that ends with dumping toxic liquid into a leaky artificial lake as seem with certain mining processes.

They're injecting treated sewage, which seems like a win-win.

> However, since October 16, 1997, the Geysers steam field has been recharged by injection of treated sewage effluent, producing approximately 77 megawatts of capacity in 2004... The injection of wastewater to the Geysers protects local waterways and Clear Lake by diverting effluent which used to be put into surface waters, and has produced electricity without releasing greenhouse gases into the atmosphere.

Interestingly, the source report calculates this, though the article doesn't mention the distinction: https://pubs.usgs.gov/circ/1441/circ1441.pdf#page=50

95100 Mgal/day fresh water withdrawn, 3760 Mgal/day consumed.

Even worse, the "pipe and tank" diagram from OP shows total water consumption, which includes seawater! (37800 million gallons per day "withdrawn", though we are not exactly worried about running out of seawater right now)

Additionally, the article doesn't mention hydroelectric at all, and the report says it's out of scope. (Almost all the water coming out of a dam is either consumed or allowed to discharge into the sea)

Strictly speaking, water is almost never consumed. The molecule is nearly indestructible.

Only chlorophyll in plants, I think?

dat hydrolysis

"Supported by a solar panel to power a fan and heater, which speed the cycles, the device produces up to 1.3 liters of water per kilogram of MOF per day from desert air."

This is pretty good, but not yet amazing. It's more energy efficient than a compressor-based dehumidifier, but probably still less efficient than trucking water in from somewhere a few hundred miles away where it's plentiful.

Either way, the big question to me is how well it will hold up over hundreds of cycles - there's no report here that I see on whether or not the MOF will also trap dust particles and other things that are likely to decrease efficiency over time.

>but probably still less efficient than trucking water in from somewhere a few hundred miles away where it's plentiful

I think the convenience and self-sufficiency factor might outweigh the raw efficiency considerations. Petrol and trucks aren't readily available to every villager. With this, there is no more worry about meeting the water truck and doing without. A big concern is what the lifespan of MOFs are. If it can be used for decades with minimal maintenance, it could be a game changer. If not, it would be back to the water truck!

You have to keep in mind that trucking in water isn't feasible in a lot of places. Sure, in developed nations there is a good road infrastructure, but it's rarer the further out you go. And it's usually the further out you go that water is more needed. Then, even if you do have a road, have to consider the water truck breaking down, the driver not showing up, etc.

Even in developed nations, a water truck doesn't always work, for instance dirt roads with steep inclines and sharp turns.

>Then, even if you do have a road, have to consider the water truck breaking down, the driver not showing up, etc.

Or militants shooting the driver, hijacking the truck, etc.

Less efficient than trucking water? Only if you have a solar powered truck.

Trucks become solar powered when you put biodiesel in them.

But seriously, there comes a point when it's more efficient to build housing for people that is closer to sources of clean water. Whatever they are doing out there in the desert without water and infrastructure probably isn't very productive in the first place, and if they can't even do it sustainably, we should question what the point of it is. Not every environment is suitable for human occupation. How many billions of dollars would you spend shipping bottled water to the moon before you put your foot down and tell people to stop living there?

What if the entire of the USA was a desolate wasteland in 100 years, due to climate change, but Russia was a verdant paradise. Is your expectation everyone goes where its productive still?

Either they move, or die. That's presuming nuclear powered desalination on a massive scale never becomes viable.

I don't think there are any realistic outcomes to such a scenario that don't involve immense loss of life.

Yes because even the russians have to move further north.

People living in the desert put in wells like everywhere else that's rural, at least those who can afford it do.

In my experience the desert isn't particularly unsuitable for human occupation. Barren wasteland deserts of endless dunes from the movies like the Sahara are not the normal. Certainly not in the USA.

What I find is the desert tends to be relatively undesirable land so it's very affordable and abundant. This has the effect of selecting for poor residents who want land of their own but can't afford anything better than desert property, and often can't afford to install a well once they've bought the land. What usually happens is their water gets hauled either by themselves or by a commercial service from the nearest city water supply, it's mostly an inconvenience.

Having a system that can directly take atmospheric air and solar energy to produce drinking water on-site for substantially less cost than installing a well would be life-changing for many of these folks. At the very least it would improve their water security since relying on an automobile for your only source of potable water isn't exactly ideal. Presumably one doesn't even need a permit from the county to start extracting water from the air with a device the size of a microwave. This is a huge difference in barrier to entry, especially for the poor.

I'm guessing you have no desert experience based on your comment. I live in the Mojave and it's actually quite nice for most of the year. There's such an abundant aquifer near me that Cadiz, Inc. is embroiled in controversy over plans to bottle and sell its water. [0]

Here's some food for thought: It's often claimed that mosquitoes have killed more than half the people who have ever lived. Guess what isn't a problem in the desert? Mosquitoes. I recently visited northern MN and frankly find my desert land far more suitable to human occupation than that mosquito infested swamp.

[0] https://www.latimes.com/local/lanow/la-me-trump-cadiz-201704...

If you have a well, or the infrastructure to ship in water, then you're not in the situation I was talking about, are you? I didn't say people shouldn't live in deserts. I said that people shouldn't live in deserts if they cannot acquire safe drinking water.

Either you figure out a way to get water, or you move to someplace where you can (perhaps another location in that same desert, but closer to a road that water trucks can navigate?) Such is the tyranny of our basic biological needs.

Except it's rather precarious to rely on hauling water with automobiles.

If this contraption works and is reliable it effectively turns all desert land into land w/potable water.

Why should we disregard this progress and what it enables?

(Just so we're clear, it almost certainly won't work, just as it hasn't all the other times it's been proposed.)

If it works for you and you're paying for it, then more power to you. If it works and the rest of society is paying for it, subsidizing your lifestyle, then it becomes reasonable to figure out what the most efficient method of ensuring you have access to water is. If funding the installation of these devices is more efficient than relocating you, then great. However if relocating your community makes more ecological and economic sense, then you should either find a way to support yourself, or accept relocation.

> I recently visited northern MN and frankly find my desert land far more suitable to human occupation than that mosquito infested swamp.

I suspect, though, that you're not trying to grow your own food. If you were, you might find the desert to be less suitable to human occupation than Minnesota.

> I suspect, though, that you're not trying to grow your own food. If you were, you might find the desert to be less suitable to human occupation than Minnesota.

Ahem - Yuma. Where your salad probably came from (maybe with some food-borne illness thrown in, but that's another discussion)...

Not sure why you're being downvoted, there definitely is a lot of agriculture in the California and Arizona deserts.

Sure. newnewpdro said Cadiz in the Mojave, though. They grow something there (pistachios?), but in very small quantity. It's not Yuma. They don't have the Colorado as a water source there.

Oddly enough, I go to Cadiz (California) on vacation sometimes...

> Oddly enough, I go to Cadiz (California) on vacation sometimes...

What do you do there for vacation? I wasn't aware there was anything out there other than some industry like the evaporative ponds on the wikipedia page...

Watch trains. Be alone. (Hey, I'm an introvert.)

And there's some kind of orchards, though they aren't very big.

The only reason agriculture is successful in Arizona is because they pump all the water out of the Colorado River to irrigate everything. As a result, the people in Mexico, farther downstream, have been screwed out of using this river.

Why?

There are fewer pests to deal with in the desert in general. From what I've seen driving past area farms the main investment is canopies presumably to help retain a more humid environment and reduce the amount of sunlight.

As an individual I can easily have a little greenhouse outside, I certainly have enough space.

It's something I intend to do eventually, but it's pretty far down the priority list at this time.

With a greenhouse (or a canopy), do you have enough water to grow even one person's needed supply of food? If not, you're importing water, just in a different form.

Or are you part of the Cadiz Water company? If so, yes, you probably have enough water.

I currently live in the high desert in southern Cali. don't have a well yet. I truck in all my water. since I don't have a well, the local electricity co-op won't connect my property. since I don't have power, I don't have a street address. I've got a decent solar setup that I've put together though. a product like this would definitely make life easier. we make up for the lack of mosquitoes here with an impressive abundance of flies...

Please read Walking with the Comrades by Arundhati Roy [1] to understand why sometimes it is not okay to ask people to move from where they are living.

[1] Original link not working https://webcache.googleusercontent.com/search?q=cache:1rpmFi...

Well they can stay and die of thirst, or stay and figure out a way of getting water. But if the only way for them to get water is immensely inefficient, then it's perfectly reasonable and moral for whoever is footing the bill to spend a more reasonable sum of money relocating the community in question. I reject the notion that anybody is entitled to a ecologically unsustainable lifestyle.

Consider Centralia PA. Was it reasonable for the government to buy out a community that could no longer reasonably exist due to local environmental factors, leaving a few stubborn people behind to fend for themselves? Yes. Because if you really want to live on top of a coal mine fire, that's on you. Relocating the community is more feasible than trying to salvage it.

Statement 1: People living in the "wrong" place must be moved to the "right" place.

Statement 2: I refuse to provide additional financial accommodations to people living in the "wrong" place compared to those living in the "right" place.

The two are very different statements. Statement 1 is much less defensible position than statement 2, even though even 2 can be problematic. You seemed to hold statement 1 as your position in the first comment and sort of acknowledged statement 2 in your second. Please don't espouse statement 1, is all I am saying.

> "You seemed to hold statement 1 as your position in the first comment"

That may have been your read of it, but that was not my intention. If somebody wants to stay behind, as some in Centralia did, that's their perogative. Society has an obligation to help people meet their basic requirements, but the form that assistance comes in is another matter. The assistance may very well be in the form of "we can't afford to support your lifestyle in that location, so we'll pay you to move."

If moon men figure out a way to pull water out of rocks, that's wonderful for them. But if they want me to give them water, I'll be glad to give them all they need as soon as they come back to earth. They're entitled to clean water, but not clean water on the moon.

>Statement 1: People living in the "wrong" place must be moved to the "right" place. >Statement 1 is much less defensible position than statement 2

How is this not defensible at all? It's perfectly reasonable. Let's go back to Centralia PA: how exactly do you propose the government make that town safe to live in when there's a coal fire underneath it which has been burning for 50 years? It that doesn't qualify as "the wrong place", I don't know what does. You can cry about moral problems all you want, but the laws of physics (which govern coal fires) really don't care about human morals and ethics.

Let's come up with an even more extreme example: NASA determines a space rock is going to strike your town (of ~10,000) next year and wipe it out. Let's assume that somehow their accuracy is excellent. There's nowhere near enough time to come up with a way of rerouting this killer asteroid (after all, we've never done that before and don't really have the technology), and luckily it's only big enough to wipe out your town, instead of causing planetary-level destruction. The government wants to relocate everyone to safety. Are you saying this is wrong somehow, and that the government should somehow make this town safe from asteroid impacts? That's truly insane.

Imagine the apes said it's foolish to invest in making hides from animals, that we shouldn't invest in the technology and just stay in Africa, as opposed to migrating to Europe, which is too cold for humans to live in.

Having in mind that all ape species in Europe except one where extinct with most of the european megafauna, it seemed the right move in retrospective.

> whether or not the MOF will also trap dust particles and other things

This is the crux of the matter, yes. Of course you will need filtration to avoid clogging your MOF with sand and dust. Then you increase the power draw, having to push the air through a filter, and you have added a potentially expensive consumable.

As TFA states, people have been making MOFs since the mid 90s. And people have been scrambling for applications since. The unanswered questions are, as always: Can they be made cheaply enough? Do they last long enough?

As per the article, they can make and Aluminium based MOF for $3 per kilo, so yes.

I believe it states the price of the aluminum is $3/kg, as opposed to the more expensive zirconium. I don't think they'd know the price of the finished MOF at this stage.

It says bulk aluminum costs $3 per kilo, not MOF-303.

I want to hear more about the bit mentioned at the end:

> At the meeting, Thomas Rayder, a graduate student at Boston College, reported building on the idea. He encapsulated a pair of enzymelike catalysts in a zirconium-based MOF to drive a series of reactions that convert gaseous CO2 to methanol, a liquid fuel.

> When they were unprotected by the MOFs, Rayder found, the two catalysts didn’t produce any methanol because they were quickly deactivated, likely by reacting with each other. But safely ensconced in the MOFs, they could make methanol at temperatures and pressures far below those used in existing methanol plants, offering a potentially cheaper and greener way to make the fuel.

The paper probably isn't out yet. But there is quite some previous research on using MOFs to make fuel from CO2:

https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=MOF+...

The challenge in that regard is always: turning CO2 to fuel takes at least as much chemical energy as was released from burning the fuel to CO2 in the first place. If you have that (presumably emissions-free) energy available, it's infinitely better to not burn the fuel in the first place and use the emissions-free energy for something else.

Unless you don’t have storage that is competitive with the energy density of carbon fuels.

Could you put a nuclear power plant far away from human civilization, and then use nuclear power to convert excess atmospheric CO2 to liquid fuel, and ship the liquid back to civilization? Reduces the NIMBYism (and risk) of nuclear, while also reducing atmospheric CO2.

I'm not sure there's a place far away enough, while still relatively free from regular natural disasters (and human disasters, like war). It's not like high-voltage transmissions lines are very lossy, so if putting plants far away was enough to assuage the nuclear fears, we'd probably have them already.

The main problem with putting nuclear reactors far enough away from everyone is that they need to be cooled, which means a water supply. There aren't that many places that have plenty of water for cooling, but no people. And most of the places that do fit that description already have a nuclear power station.

Yeah, in theory. But nuclear NIMBYism might prove too strong for even that. It will be interesting (scary) to see how this game of chicken plays out. Will fear of nuclear prevail for much longer over fear of climate change?

We already do this, just with corn instead of MOFs

Yes, but batteries can't do everything yet. To whatever extent we keep using liquid fuels, it'd be nice if they were carbon neutral.

Ammonia. Liquid or compressed hydrogen. There's several options that are just as feasible with nice energy densities and that reduce CO2 emissions much faster.

But it allows you to take energy which was generated from renewable and use it with existing fossil-fuel infrastructure.

It seems everybody wants to be a moisture farmer, but these "novel dehumidifier in the desert" schemes have thusfar always failed.

So did building flight machines for quite a while...

On one hand, it's important to keep an open mind. On the other hand, when you're dealing with a subject that's been a scam magnet for decades, more than a little skepticism is warranted.

Airplanes worked out, but 'dehumidifiers in the desert' is close to flying car territory. (https://en.wikipedia.org/wiki/Moller_M400_Skycar)

>Airplanes worked out, but 'dehumidifiers in the desert' is close to flying car territory.

why do you see that remaining the case in the coming couple decades?

Bayesian reasoning? How many times do you touch the stove before you get cynical and expect hot stoves to hurt?

Desiccant/absorption dehumidifiers are nothing new. I've been around the block enough times to recognize the hype cycle. The motivation of the inventor seems pure, and the first order analysis seems to make sense. Dehumidifiers do indeed pull water out of the air, so it seems plausible that this tech could one day be used to quench the thirst of people living in deserts. The moller skycar scam has gone on for decades in no small part due to how reasonable it sounds. We know machines can fly, so why not a road-worthy aircraft? On the surface it makes sense, so the scam finds plenty of marks. But the devil is in the details.

Aside from the fact that there isn't much water in dry air, 2257kJ of enthalpy is released for every kilogram of water pulled from air and that's a lot of heat to get rid of somewhere. Most mature cooling technologies (peltier, compressor,etc) have a COP value smaller than 1 so in other words it will take even more energy to harvest water efficiently. Trucking water might actually be cheaper.

We are currently at the moment where every aerospace manufacturer in the world is building some kind of autonomous sky taxi... seems like every idea has its time and specific technical requirements.

I recently found out that Opener is getting funding from Larry Page for theirs. It certainly is technologically feasible to build such a machine that actually flies. But the question is, are they making yet another glorified ultralight? Or are they really going to give us the flying car in every garage dream promised to us by the Jetsons?

If they're proposing an ultralight, I'm not too skeptical. Loads of companies have successfully created ultralights. If however they're trying to sell me the dream, like Moller, then more skepticism is warranted. There are a lot of problems with the dream that aren't really problems for limited production ultralights. For instance, the simple matter of how much low air traffic is tolerable to the community. Or the incidence rate of poorly maintained aircraft falling out of the sky and crashing through my living room ceiling.

If these MOF people were talking about more efficient desiccant dehumidification, I wouldn't be nearly so skeptical. But by making it about the noble feel-good mission of drinking water from thin air, they're sending out a different sort of signal. It tells me they're looking for hype, and the way they're doing it has a past association with scams that I can't rightly ignore.

Everyone is building one, but no one has really proven that the market really exists. The cost-estimates I've heard are cheaper than helicopters, but in the same order of magnitude. These UAM vehicles are going to replace helicopters, not your car-based Uber ride.

I never wanted to be a moisture farmer, I just wanted to go to Tosche Station to pick up some power converters!

Although, realistically, it could still be useful in non-desert places? How about drinking water on ocean vessels?

Every time I visit a place like the Akihabara I am semi disappointed to not see a guy hawking transformers and power supplies at a booth named "Tosche Station".

Most ocean vessels will have a reverse osmosis "watermaker" to convert salt water to fresh water

https://en.wikipedia.org/wiki/Watermaker

Which require regular maintenance and the primary membrane, a wear item, isn't exactly cheap to replace.

Having more options is definitely welcome.

Salty water + open sea permanent wooble + life saving device made of a delicate tiny mesh of rustable metal

Looks like a great plan, can't see what could fail. Look, a big wave approaching by starboard... :-)

I bet if they included a droid that speaks the binary language of moisture vaporators, it'd make things go a lot more smoothly.

Indeed, but contrary to typical articles who basically headline "WATER FROM THIN AIR!" this one actually explains the novelty of the process and acknowledges it depends on air humidity. It is not just a solar-powered condenser.

And actually the whole material itself seems to be very interesting and has the potential to have a lot of industrial applications.

Of course they failed. Just buy a dehumidifier and see how much water you get.

True, but we can fail many times, and we need to not fail only once...

I would love to be wrong and stupid, but can't fall to think in another Theranos when I read this. Maybe is the style of the writing, dunno. Of course sucking all the water from the desert air would have a profound impact on its vegetation and fauna.

Unless we are talking about coastal waters, importing trucks of water from areas with more vegetation and water excedent seems a more economic and sensible solution.

The thermodynamics of this rarely matches peoples' optimism about it.

https://www.youtube.com/results?search_query=thunderf00t+wat...

This is really interesting! As someone who lives in the desert, I would want one of these.

But nothing comes for free - it seems like the output would be dependent on the humidity level of the air. If everyone was running these, would it be as effective? My gut says yes, just due to how much airmass there is, and even the heat from the ground should provide some mixing. But I am not sure of the napkin calculation, which I'm sure they've done.

Also at higher temperatures, the air can hold _more_ water vapor. This is why humidity is relative to the maximum amount of water the air can hold.

The CO2 capture potential is also really impressive.

[edit: got it backward as to temp vs holding capacity, doh.]

It's the other way around, at lower temperatures the air can hold less water vapor. That's why you see condensation forming on cold things.

Doh, you're totally right. Although still, in the desert, there isn't much water in the air even if it's really hot.

https://www.engineeringtoolbox.com/moisture-holding-capacity...

Easy to get confused because humidity % tends to be higher at a lower temperature (morning dew for example).

Why is this?

Say you have a given amount of water vapor in the air. Relative humidity as a percentage reflects the amount of water vapor in the air compared with the maximum amount of water vapor the air could hold at that temperature (and pressure). The amount of water vapor the air can hold depends on the temperature, with higher temperatures able to carry more water vapor.

As the temperature goes down, the amount of water vapor stays the same while the amount the air can carry decreases, so the relative humidity goes up.

https://en.wikipedia.org/wiki/Relative_humidity

I believe it's simply a matter of colder air increasing in density so there's less space for the water vapor. When the air heats up, it expands and can hold more vapor in the increased volume.

There's more water vapour in the air in the middle of the Sahara desert than there is in the air in the middle of Greenland while it's actually snowing.

So, is this the first step of making windtraps[0] a reality?

[0]: https://dune.fandom.com/wiki/Windtrap

Yeah, my first thoughts too!

Looks like the next "crowd funding scam" we see alot lately.

Ill wait some time for someone to do a napkin math to debunk that as a valid product.

It’s published in a reputable journal, I’d say it’s more than a crowdfunding scam.

I wonder if the MOFs self assemble. I just started searching, but if any experts here know how they're made, please explain. I found an article that says the organic linkers are "ditopic or polytopic organic carboxylates (and other similar negatively charged molecules)," but MOFs are crystalline, so do they have to be baked? I get the impression that they're pretty easy to create, and can be designed to have affinity for any molecule. I really wonder if hydrogen storage will ever be solved. https://science.sciencemag.org/content/341/6149/1230444

What about he environmental impact of sucking the small amount of water present in the air out of it? I am sure some animal or plant depends on it. Don't get me wrong, I would let an animal die to save a human any day, but is this needed? Seems people having been making due in these climates for thousands of years. If this is as good as they claim this will only attract people to these locations instead of places which already have an abundance of water, since people generally find arid climates more comfortable than humid ones.

The amount of air that can pass through a microwave size device is miniscule compared to the amount of air over a desert.

Seems logical to see that after all these Dune related posts on HN.

How much more effective are they versus low tech alternatives like: https://www.nydailynews.com/news/world/world-driest-desert-c...

I wonder what impact will this have on the desert itself

Seems like a good way to eliminate a lot of life in the desert. Presumably that air moisture gets cycled through the plants and animals in that environment. No water = no life.

Mind you, humans have already drastically altered the deserts by rerouting rivers and building dams, so it wouldn't be the first time an environment has been changed by technology

Heh it's the Lars Moisture Farm

Now set a restriction on pollution or kill it so there is no trace.

Else this man's water will be polluted. Thats how you pay respect, not by using more of your intellect.

probably I'm paranoid but I worry this could be one of those kinds of inventions humans are good at that in small amounts are really beneficial but when scaled up start to have unintended harmful side effects only by then it's too late or too big to stop.

I'm not sure it'll be scaled up to the point where it would affect things in a big way. We've had technology that can extract water from air with electricity for well over a hundred years (vapour compression refrigeration) and so far it hasn't caused any issues.

The ocean is a huge source of water with a massive surface area which would constantly provide a source of humidity, and the lower vapour pressure caused by removing water from air in substantial amounts would encourage further evaporation.

That said, local effects would be more pronounced than global effects.

Wow

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