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> in places where the air is wet, it rains, and you don't need it.

- Rain water collected in ponds/rivers may be contaminated/infested.

- Lack of fresh water in the ocean/islands is also an issue.

The two things that are available almost everywhere are air and sun.

Rainwater cisterns are a viable option if you have rain.

And if you dont?

Then you probably don't have humidity either, so the collector won't work.

There are many places that have fog, but no or little rain - the skeleton coast inwards/Namib desert in Namibia for example.

There's a very interesting beetle there...

No, that's not true; it's just less efficient because you have to handle more air and cool it to a lower temperature. Air in Earth's atmosphere always has significant humidity. See https://news.ycombinator.com/item?id=30716765 for some calculations.

It's reasonable to condense drinking/cooking water from air with solar energy in places that lack secure water. Not water for other purposes; you can't run a cooling tower, irrigate a field or an orchard, water a herd of cattle, or even grow a garden that way. But a household-sized dehumidifier powered by a household-sized solar panel can certainly make enough water to drink and cook rice.

On the other hand, if you live in semi-arid desert or any wetter biome, a cistern probably has a better cost-benefit ratio. Depending on your aquifer, a well may be better still.

It's worth pointing out that the sorbent-based systems in the H2E project don't work by cooling air below ambient temperature.

I will never check out a Thunderfoot video. He is a hateful pitiful man.

He's generally not wrong. But I agree, his approach is pretty obnoxious.

But aren’t the “debunkings” rather cursory and dismissive?

Instead I think real engineering relies on tradeoffs, certain areas of a multidimensional space where an idea makes sense - and others where it doesn’t.

Watch them and find out? He explains why it takes so much energy to boil and condense water, calculates out and explains how many Joules to condense a litre of water, how long that would take for various solar panel sizes, compares the solar-water-collector against mains powered dehumidifiers, compares the solar collectors against using the same size panel as a rainwater catcher in different environments, compares it against the price and time to get 10,000 litres of water in a tanker and drive it a thousand kilometers, talks about the product's claimed size, isntallation cost or use cases and how they don't make sense.

I see his style is divisive, but I don't think they are cursory, at least the two I linked; he's clearly put hours of time into making them, it's not just him talking and laughing recorded in 20 minutes.

This doesn't use solar electric though. It (mainly) uses direct solar heat. It also doesn't use any kind of peltier cooling. It's a largely passive device with a few minor electric components that won't draw much power.

People using his "rather cursory and dismissive" debunking to debunk other very different technology is kind of annoying.

Ok? But he’s still right.

Their paper is open access: https://www.nature.com/articles/s41586-021-03900-w

They claim that this device with 1m² footprint could "well within thermodynamic limits" alleviate thirst for a billion people living in "tropical regions" (daytime relative humidity 30%-90%).

I already look forward to the debunk. It all seems very high-level. My money is on that these regions where the device would be viable do not actually suffer of lack of access to drinking water to start with - not to the tune of a billion thirsty people at least.

> "I already look forward to the debunk."

How about: Google found a way to alleviate thirst for a billion people and then decided it wasn't worth bothering with, stopped it being a project, and dumped the plans on Github? Norman Borlaug[1] won a Nobel Prize for his contribution to food production which is said to have fed a billion people, so I guess these authors had better things to do at Google than save a billion thirsty people and do Nobel level work?

From the paper: "Our assessment introduces a hypothetical 1-metre-square device with a SY profile of 0.2 to 2.5 litres per kilowatt-hour".

From the Thunderf00t video, checks out with a Google: it takes about 2,200,000 Joules of energy to evaporate 1 litre of water at 100C into steam at 100C, and so at least that much to condense 1 Litre of water from steam. There's 3.6MJ in 1KWh which is enough for 1.5 Litres. So already in the first paragraph of the abstract their upper estimate of 2.5 litres per KWh seems to be beyond thermodynamic limits (I could be very wrong, I'm no scientist; am I wrong?).

I'm not claiming any expertise or more knowledge than watching two videos just now, but their paper describes more than just solar powered condensing, with absorbent gels and materials involved as well (but still, wouldn't those have to take the same amount of energy out of the air to condense the water?). Their paper also shows desalination as being >100x more water per KWh than getting water from air.

[1] https://en.wikipedia.org/wiki/Norman_Borlaug

Thunderf00t is hit and miss. Some videos are scepticism, small mindedness, long pessimistic rant without substance and no debunking

Which debunking video was like that?

"Veritasium: BUSTED!" https://www.youtube.com/watch?v=5Hyy1zRZPiQ This is his area of expertise and is a great "busting" video

Trash: "Elon Musk Invents UNDERGROUND Traffic Jam!" "Tesla Bot" No debunking. Small mindedness, pessimistic rant. Just says Elon will fail but not clear how he knows he will fail

He actually has outlined exactly what's wrong with these ideas. I mean the hyperloop was supposed to be "like an air hockey table", well guess what, musk now "advocates for wheels"... It's just a really bad and unworkable idea. The idea of 1000km long vacuum tubes is beyond stupid, when we already have high speed rail. Please tell me how stating these facts are "small minded" or "pessimistic".

His main point is usually about the massive unwarranted hype and blind hero worship around these concepts, and usually scams (the water stuff and other kickstarter projects).

The truth hurts, I guess.

I never mentioned hyperloop. Again this is the level of reply I would expect of Thunderf00t. You can do better

This relates to hyperloop "Elon Musk Invents UNDERGROUND Traffic Jam!"

That video is about the Boring Company. They are making tunnels not hyperloops

Sure, some videos are more of a rant and he can come across abrasive but I think the fundamental arguments are valid. Hyperloop isn't a viable concept ever since it's been conceived over a century ago. And the tunnel projects have so far been underwhelming and universally panned as worse than a standard lightrail or subway.

The only thing that's relatively unknown is the "Tesla Bot" but considering that self-driving AI is still unsolved, let alone any kind of general intelligence, I don't think there's much behind that either.

A commercial system is in use on the Warm Springs reservation in Oregon: https://www.opb.org/article/2021/08/10/warm-springs-leaders-...

Dehumidifiers aren't what's thermodynamically impossible, of course; Fontus was just making quantitative performance claims that were thermodynamically impossible about how small their system would be and how little energy it would use.

You don't need to sink to citing YouTubers to figure out how much water air contains. You can just consult a standard psychrometric chart: https://commons.wikimedia.org/wiki/File:PsychrometricChart.S...

You can see from that chart that at, for example, 20 degrees and 30% relative humidity (which, if you're not aware, is pretty dry), you have about 5 mg of water per gram of air, or about 5 grams of water per kg of air, which is about 0.8 cubic meters (1.2 g/liter). So if you want to produce 10 liters of water per day for your family, you need to run 2,000 cubic meters of air through your dehumidifier. (Or a bit more because you can't reduce it to 0% humidity.)

That might sound like a lot, but it's per day, so it works out to 49 cfm, which is not "big fans and lots of power". If we're talking about a 300 mm square aperture it's 260 mm/s of airflow, a breeze you can barely feel, which requires a totally insignificant amount of power compared to the actual refrigeration involved. This is not going to fit nicely on your bicycle like in the fraudulent Fontus videos but it is entirely reasonable as a household appliance.

Solar electricity is free if you aren't using it for something else.

As for bacterial growth and filtering, yeah, that's a real design constraint, and it's one that HVAC systems have fallen down on in the past with disastrous results, but it's not some kind of unsolved engineering problem. Every air conditioner, sea voyage, and water tower deals with it. Here in Argentina just about every house has a rooftop drinking-water tank, where we control bacterial growth with chlorination, by impregnating the tank plastic with bacteriostatic agents, and by making the tanks opaque so algae can't grow. Thousands of years ago, mariners dealt with it by dropping a silver coin in each amphora of drinking water.

It would be a more difficult problem if a dehumidifier were warm and moist, but actually it's cold and moist.

As for the relative costs of tankers and electricity, well, that varies depending on where you are. Around here supply chains are so unreliable that I'd hate to rely on a weekly delivery from a water tanker in order to not die of thirst in 48 hours. (Fortunately, I live a few kilometers from the biggest river in the world. Water is not a problem here, though in places pollution is.)

You also need power to take the heat away that is created when the water in the air turns into a liquid. Best case you need to cool for about 0.7kwh per litre of water you make. That means for your 10 litre example you need best case 7kwh. That is a decent sized solar array and if you have any inefficiencies in your heat pump setup it gets much worse. Also you assume per day - solar only works during the day so you need storage as well so your system can work during the night.

Yes, that's why I said moving the air takes "a totally insignificant amount of power compared to the actual refrigeration involved." You're talking about the actual refrigeration.

The terminology you need to google for "the heat that is created when the water in the air turns into a liquid" is "enthalpy of vaporization of water"; around room temperature this is about 2.4 MJ/kg, so 10 liters/day is 24 MJ/day, which is 6.8 kWh/day, or, in SI units, 280 watts. However, remember that a heat engine operating at the Carnot limit is reversible. The coefficient of performance of a typical heat pump at these temperatures, the kind you might buy off the shelf at a big-box hardware store, is about 2, so you only need about 12 MJ/day (3.4 kWh/day, 140 watts). At a typical desert capacity factor of 25% this means you need a 560-watt solar array, about US$120 and three square meters. (California's utility-scale PV average capacity factor was 29% last I looked.) Very cloudy and polar places can have PV capacity factors as low as 10%, but they also have easier sources of drinking water. Like a rain barrel.

It's easier to store water or to "store coldness" than to store electricity, so you don't need electrical storage, you just need a heat pump sized for your peak throughput instead of your average throughput. Heat pumps are pretty expensive, so you might think this is a big problem, but the cheapest air conditioners I can find for sale around here are about 2000 watts, not 500 watts.

I've been noodling on desiccant-powered heat pumps for this and other uses, which may be able to reduce the cost of such systems, gather a larger fraction of solar energy than the 21% of high-efficiency PV panels, and provide built-in energy storage.

It's worth noting that the Nature paper abstract https://www.nature.com/articles/s41586-021-03900-w.pdf claims they're spending as little as 0.4kWh/ℓ, which is less than the 0.68kWh/ℓ of the enthalpy of vaporization, though more than the 0.34kWh/ℓ of the enthalpy of vaporization divided by the CoP of a commonplace vapor-compression heat pump. (They point out that "solar-driven cooler–condenser devices suffer from a steep loss in electric energy conversion", by which I think they mean photovoltaic panels are only about 21% efficient, so you lose 79% of your sunlight before it can start driving your compressor.) They're using a sorbent-based cycle rather than a vapor-compression cycle. I should have read this before commenting.

They cite a paper by Kim et al. that calculates the thermodynamic limits on the specific yield of atmospheric water harvesting as 5–50 ℓ/kWh (0.02–0.2 kWh/ℓ), which I suppose depends on the air temperature and humidity.

> "You don't need to sink to citing YouTubers"

You say, whiloe going through the same calculations as Thunderf00t makes, to make the same points he makes. Including: how it is possible to do it, how dehumidifiers exist, what humidity means, how far out the Fontus design sizes were from being practically workable. 49cfm assuming you get solar power 24/7. Double or triple that to get it through while the sun is shining. I happened to see this[2] video of someone who put solar water generators on his house and reviewed it after a year. Check out from time 2:06 we can hear the fans running and see how "barely noticable" they are. (Insignificant power compared to refrigeration, I agree with). Said review video also includes a complaint about the water being unpleasantly warm to drink, because the whole system is on the roof of their house in the sun and the pipes all get warm.

> "Around here supply chains are so unreliable that I'd hate to rely on a weekly delivery from a water tanker in order to not die of thirst in 48 hours."

This comment is weird because I imagine you don't actually right now have a solar-water-dehumidifier providing water for your family so that you don't die in 48 hours when your water supply fails? If not, why not?

[2] https://youtu.be/VQRAtwz3Igs?t=126*

> You say, while going through the same calculations as Thunderf00t makes, to make the same points he makes

Right, but people reading my comment don't have to sit through a long video of some guy yelling at them to see that the calculations are correct. And they can see your correction to the airflow calculation immediately below my comment:

> Double or triple that to get it through while the sun is shining.

I'd say quadruple, given the typical 25% capacity factor for utility-scale PV in the desert in the US. (Quintuple or more if you aren't in the desert — but then you can just use a rain barrel.) I should have included that correction in my comment, and I appreciate that you took the time to point it out.

> we can hear the fans running and see how "barely noticeable" they are

It's all a matter of ducting cross-sectional area. 10k m³ per day is 120 ℓ/s; through a 100-mm-diameter round duct that's 15 meters per second, or 55 km/h, "near gale" on the Beaufort scale. The same 120 ℓ/s through a one-square-meter aperture is 120 mm/s, a wind speed where smoke from a chimney rises vertically.

> This comment is weird because I imagine you don't actually right now have a solar-water-dehumidifier providing water for your family so that you don't die in 48 hours when your water supply fails? If not, why not?

I don't live in the sort of desert where a solar dehumidifier would be a better option than a cistern; I live next to the widest river in the world. If I dig a hole in the sandy soil, after about three meters I have to stop digging unless I have an electric water pump running 24/7 to keep the hole from filling up with water. I don't know how things are where you're from, but here in Argentina, we have municipal water supplies run through pipes, supplied by water treatment plants. Unlike truckers, the pipes don't go on strike, call in sick, or get hijacked by asphalt pirates, and if a worker at the plant does, another worker can fill in for them. There's a 1000-liter water tank on the roof which takes about three days to empty when the water main does cut out. (Yes, sometimes that means it gets unpleasantly warm.) Dozens of grocery stores are a short walk away, replete with bottled water and soft drinks. We get 1200 mm of rain a year. In fact, it's raining right now.

A friend of mine lives in a nearby suburb that doesn't have a municipal water supply and where the river water is too polluted to drink safely. Her roof drains into a rain barrel.

My family members who live in semi-arid deserts without municipal water systems drill wells. (One of them actually has a dug well, the kind you could fall into, predating the municipal water supply.) The aquifers reached by the wells go lower every year, and sometimes you have to go and drill them deeper. In such places, civilizations like that of the ancestral Puebloans have collapsed during centuries of drought. People living in such places today without well-drilling equipment often spend many hours a week walking to water sources and carrying the water back home.

Many deserts today have no permanent inhabitants because of such considerations — you can only stay there until you run out of the water you brought with you. Burning Man is held in such a place, but not the driest one; there are places in the Atacama where rainfall has never been recorded. Theoretically a permanent settlement in such a place could rely on weekly water tankers driving in from wetter regions, but, for the reasons I outline above, only theoretically. Household-scale solar dehumidifiers are a much more feasible solution.

The more important reason my comment is weird is that it engages in factual and logical exploration of things that currently do not exist, but could, based on objectively verifiable information about the world. Your comment is weird in the same way, and I appreciate that. Let's have more weird comments.

" It's a dehumidifier; in places where the air is wet, it rains, and you don't need it. In places where you need it, you need it because there's not much water, so it doesn't work well."

I wonder how well it would work as a stand in for a desalination solution. Where there's all the water you want but it has salt (or other contaminant) that makes it impossible to drink. Seems to me that a beach would be the perfect place for it. At $150 price point it's a very good alternative to high price machinery.

Desalination produces a lot more water-per-KWh-energy than unboiling water from the atmosphere. Elsewhere in this thread someone linked a paper which estimates up to 100 litres per KWh for desalination, vs ~1 litre per KWh for condensing.

Saving on machinery, or chemicals, might be important but $150 of materials for a device will buy you ~25,000 litres of water in bulk (in the USA).

I don't have views on the credibility of specific technologies but I've hoped that these could be viable in places like coastal California where fog provides quite a bit of air moisture but it never rains--do you not agree with that?

If you have fog or dew, you can just use a fog net: https://en.wikipedia.org/wiki/Fog_collection https://news.climate.columbia.edu/2011/03/07/the-fog-collect...

These are mentioned in Table 1 of the Nature article: https://www.nature.com/articles/s41586-021-03900-w.pdf

In coastal California, redwood trees have been doing this since the Jurassic.

In the conditions you describe, fog nets commonly yield 2–3 ℓ/m²/day of water (20–30 nm/second), though experimental projects have reached yields over 13 ℓ/m²/day (150 nm/s): https://www.oas.org/dsd/publications/unit/oea59e/ch12.htm

Fog nets are easier to make and easier to repair, and consequently enormously cheaper. This makes them practical not only for drinking water but even for irrigation. They are more tolerant of damage, though they do need yearly maintenance. But they don't work on days without dew, and in some places, that's nearly all days.

The linked nature paper points out that over a billion people without access to safe drinking water live in areas where their design would be high performance (tropical areas).

Very different technology, this is largely not solar-electric. It's solar-thermal with a bit of electric for a circulating fan and a small motor.