The comparison I was trying to make is that we do have the power to capture 100% of a river. This isn’t good, for obvious reasons. Humidity capture is a much different process, since we can’t just capture 100% of the humidity from a panel either. You could have 80% humidity going in, but actually still 50% relative humidity going out. And that would be maximum absorbtion performance!
As for local or regional scales, yes there could be impacts. I’m not quite as well versed in how trees affect the environments, but I suspect a local water-from-air farm would have some impacts on a local scale. If we had some data on how redwood trees absorb based on the different environmental conditions, I could run some numbers to figure out the differences and see how it would be affected.
Agreed on the impacts though, this isn’t a zero impact technology, but compared to the direct competitors it is trying to replace (groundwater harvesting or desalination), it is an improvement. A mindset I like to apply is that humanity will need water regardless of how they get it. New technologies should provide a solution that is lower impact, along with a financial incentive (cost).
Haha yes salt pools are fun, but wouldn’t always be the right kinds of salts required to create batteries. Unfortunately real chemical processes require very high purity raw ingredients, and using the reject water from an desalination plant probably wouldn’t cut it. Although if someone figured out how to make a battery out of that, that could have big potential! You’d get all the water and energy storage you would need.
MOF behaves like a sponge, but wouldn’t feel like a sponge. Squeezing it would be nice, and could definitely eliminate the hassle of having to heat it up.
As for the energy, the thermodynamics of dehumidification basically requires an external energy source. To cool the air, you have to have a heat engine which removes the active ambient thermal energy out of a system. Such a system would look like a traditional dehumidifier hooked up to solar panels. The issue with that is the associated capital expenditure costs to build up such a system, as that already costs significantly more than “some random metal sponge” (assuming we could make it at scale).
For now, the only ways to cool the air down would be to use traditional refrigeration techniques, or peltier coolers. Peltier coolers are super inefficient, and traditional heat pumps require alot of energy. When in a low humidity environment, the coefficient of performance for heat pumps goes way down because the outdoor temperature could be very high, and the humidity very low. To reduce the air temperature to below dew point would mean cooling the air to near 0c, which is pretty much putting a freezer in a desert.
Solar energy is free, but absorbing it and converting it into useful work takes a good bit of engineering effort to make happen. What MOFs and similar materials can take advantage is being able to be left out in the sun like a sun dried tomato and covered in a black painted cover. Couldn’t be simpler!
Here’s a picture of one of our tests generating water from air! We got 21kg from a large-ish panel.
I can’t show much else but I can guarantee we did harvest the water from the air.
Technically yes! To put it in perspective, there’s about 2.5kg of water in the atmosphere per m^2 of earth surface area. If you put enough panels across the earth, you could probably do a decent job at taking some of the water out of the air.
We have to look at another factor affecting the water in the air. As we take water out of the air, it’s not really a finite resource. Most water in the air generally comes from the sun evaporating the oceans. If we take the water out of the air, the sun will put the water back. There’s always a balance of humidity and quantity evaporated. When the humidity is lower, the sun would have an easier time evaporating more water due to the osmosis of the water from the source (ocean) going into the air. Osmosis is a kind of log graph, so even if the humidity is lower, the exponential tail means the solar evaporation and humidity pretty much balances out at the end of the day.
It’s similar thing to taking water from a river. If we take all the water from a river, can we dry up downstream? Yes! But considering the height of the atmosphere, it’s like standing at the edge of the river trying with a bucket and trying to scoop everything up. Unless these water-from-air harvesters can reach all the way to the clouds, we probably won’t dry anything up.
Happy to help! It is really a cool technology, but with alot of nuances. It certainly can do what they claim, but for now only in controlled environments. I got pretty close to testing a real cost effective solution, but I couldn’t see it through due to extraneous circumstances.
You’re absolutely correct that there has to be water in the air. However part of the trick to these panels is that they’re not steady state. They have a day cycle and a night cycle. During the night is where they do most of the work of absorbing the water from the air. Over a number of cycles I have overseen, the humidity in the air rises dramatically during the night. This helps these panels in terms of air extraction, since they work on a humidity basis, rather than a total-air-water-content. Think dilution or osmosis when it comes to the actual absorbtion mechanism.
When you do the math, it also doesn’t really seem like there’s alot of water in the air. Only something like 10-40 grams of water, especially depending on the outdoor temperature. We ran indoor tests with a panel a few sqm in size, and even in a small indoor warehouse, it was not able to dehumidify the warehouse to any significant levels. Maybe at most 5% humidity delta. However air is not static, and wind is always blowing, even when it seems really weak. There’s a huge amount of atmosphere above the ground, and unless the panels can absorb the water from the clouds too, the localized de-humidification that happens isn’t going to be significant. It’s like trying to suck up all water on a beach. The waves are going to replace it shortly enough.
So the one practical limit of these panels that is most frequently missed is the solar aspect. The MOF materials are like a sponge. You can absorb all the water in the air, but you still need to take the water of the MOF. The limit depends on the sensible and latent heat of the water, while in the sponge. MOF doesn’t actually really change the boiling point of water at all, so you’re really essentially creating a water distillation tower. In 1sqm of land, the most irradiance you’re going to get is about 1kw/sqm. 1kwh can boil about 10 liters of water. Taking that into account, over a 8 hour solar day. That means at most a single square meter of solar panel could generate 80 liters of water per day. It’s alot, but considering solar losses, glass loss, and thermal loss, more practical limits would probably be like 40 liters. The MOF material also required sensible heat as well, so already a huge portion of incoming solar energy is gone to heating the environment and raising temperature.
In all, you’d have to cover a huge amount of acres before this would dent the atmosphere in terms of humidity. The 1000 liters a day can really only happen when you have a large solar collection area, plus absorbtion surface area to back it up.
MOFs and other types of materials are actually a highly well researched topic. They’ve been around for decades! However in the current state of things, it’s kinda like battery technologies we see. It depends on the scale of manufacturing that these researchers can scale up production to.
Alot of time, the processes researchers do to manufacture small batches to produce a small prototype don’t work well when scaling up. The team I was working with had lots of trouble with it, but eventually settled into producing batches that would fill approximately a construction bucket worth at a time. Not a huge amount, but definitely a starting spot. It not mpossible to assembly line something like a millions of buckets a day, but at the same time your manufacturing costs go up alot.
There are many different competing kinds of water-from-air materials. These researchers use MOFs, but since they use metals, the cost to manufacture goes up significantly. Polymer based materials are a bit more “secret sauce” depending on the formulation, but they’re simpler in the sense you can use specific kinds of salts. The cost difference is something like 10x, so MOF really needs to produce 10x more value, otherwise it’s not worth it.
Since water is such a commoditized product, commercial prices are somewhere around a few dollars per cubic meter of water. When you design something that has to compete with existing products, you have to have a cost at, or less than existing prices. Either your panel has to be super cheap, or your water production has to be off the charts.
Let’s say a commercial water-from-air solar farm lasts for 30 years. Each day, 1sqm of panel produces 1 cubic meter of water. You’re only selling that water for $3 (approximate commercial rates). Over the lifetime of the panel, your income is 30years * $3 = $32850. It’s a big number! A realistic current figure for water production at best would hit 0.01 cubic meters of water. Holey cow! Now you’re actually making 1% of our original target, which is 3 cents per day, or $330 over it’s lifetime.
Selling anything that’s 1m^2 for only that price point is a crazy feat to achieve. I designed a number of systems that would try to enable that, but you must also factor in everything including installation and maintenance costs.
There’s billions of dollars thrown around to invest in these technologies. The only thing stopping it are the unit economics. You have to compete in an industry that is centuries old. But these can succeed, they can easily replace every single water filter in the world.
There’s two impacts these panels could have. There’s the solar irradiation aspect, and the air humidity aspect of them.
In the solar irradiance balance, you have a net energy in, most of which goes directly to heating the ground. A panel would aim to absorb as much as that energy as you can, most of which would go towards a phase change of the material to release the water bonds. MOFs are extremely clean in terms of their re-usability, and don’t release any other compounds into the steam when released. Think of it like a condensation system, but without having to collect any water from any ground based source.
The air humidity is the other balance. In theory you could “absorb all the water out of the air”. In most business cases, these need to be deployed to more coastal regions, not literally smack in the middle of the desert. But in such cases, the atmosphere is highly dynamic and more or less equalizes total air water content in a certain microclimate. It makes it very renewable since the sun evaporates massive amounts of water from water bodies, which can be returned via either rain, or through water harvested through water-from-air chemistry.
The industry will want to buy water regardless of where they are, so when evaluating technologies, these provide much lower impact to the environment than any existing groundwater based system.
I used to work for a company making a similar device, the chemistry behind the technology is actually a well researched topic, and there are many kinds of various chemistries that can achieve a similar effect. Silica gel packets are the most common, a cheap solution that extracts moisture from the air, but is non-reusable.
These MOF compounds are useful because they have a fundamentally different method of collecting the water molecules. The framework traps the molecules inside, which can be later released with heat. Thermal solar power is free, but does require careful management of the rest of the device such that the material can get hot enough (usually around 100c), which also providing another surface to condense the vapour. I spent alot of time designing and testing such panels. They do work! I can post pictures of fishtanks of water later.
There truly couldn’t be much of a downside to these technologies. The real alternative is desalination, which produces hyper concentrated salt pools, or well water extraction, which is also bad…
The reason these technologies is usually due to the cost effectiveness to produce the material, and to build the enclosure around the material. The panels have to scale very large to get any reasonable about of solar power, plus the condensing and collecting mechanisms also add weight and cost. Water is not an expensive product, so at the end of the day, the economics don’t always work out favourably.
Happy to answer any questions about the technology.
Actually, this isn’t quite as simple as a dew catcher. For MOFs specifically, there’s a fundamental physical chemistry principle going into it which is able to capture the water. At the molecular level, the MOF structures are super porous, which allows the water in the air to become trapped inside. The difference between that and dew catchers is dew catchers aren’t able to actually harvest gasseous H2O. They only harvest what is able to be deposited in liquid form. Water from air technology is a real thing, and there are at least decades of research on it.
You may have some experience with a slightly different form of vapor harvester, silica gel packets! Those use a chemical based methodology to bond with water molecules in the air instead. There are two major difference between those and MOFs is that MOFs are reusable, and silica gels are not quite reusable. The other difference is in the holding capacity of MOFs. They can hold significantly more water than silica based gels.
The economics of the emerging MOF field is definitely uncompetitive in it’s current form. The current price to performance ratio isn’t something that can currently compete with existing technologies, whether it is trucking water, or desalination. The industry knows this, and knows it must get the price down to competitive levels. However the reason why it is nobel prize winning this time is that now the performance is in a ballpark where it could be commercially viable. It would be more environmentally friendly to setup some solar water harvesters one time, rather than to be constantly trucking or piping in water from elsewhere. Extremely remote communities would be more self reliant if they don’t have to be paying exorbitant amounts of money each time for new water delivery.