Atmospheric water harvesting is a way to obtain fresh water in arid regions, as there is always some moisture in the air, especially in the form of morning fog. The trick lies in capturing this moisture as efficiently as possible, with a range of methods available that start at ancient low-tech methods involving passive fog droplet capture all the way to variants of what are effectively large dehumidifiers.
A less common way involves high-voltage and found itself the subject of a recent Plasma Channel video on YouTube. The inspiration for the build was a 2018 paper by [Maher Damak] et al. (PDF) titled Electrostatically driven fog collection using space charge injection.
Rather than passively waiting for dew to collect on the collector, as with many of the methods detailed in this review article by [Xiaoyi Liu] et al., this electrostatic approach pretty much does what it says on the tin. It follows the principle of electrostatic precipitators with a high-voltage emitter electrode to ionize the air and grounded collector wires. In the video a small-scale version (see top image) was first constructed, demonstrating the effectiveness. Whereas the passive grid collected virtually none of the fog from an ultrasonic fog maker, with 35 kV applied the difference was night and day. No water was collected with the first test, but with power applied a significant 40 mL was collected in 5 minutes on the small mesh.
With this scale test complete, a larger version could be designed and tested. This simplifies the emitter to a single wire connected between two stakes, one of which contains the 20 kV HV generator and battery. The mesh is placed right below it and grounded (see image). With an extreme fog test inside a terrarium, it showed a very strong effect, resulting in a harvest of 14 mL/Wh for this prototype. With a larger scale version in a real-life environment (i.e. desert) planned, it’ll be interesting to see whether this method holds up in a more realistic scenario.
Appropriate matching with hydroponics perhaps?
With the side benefit of a free electric fence to keep critters out of your veggie patch!
That’s extremely cool. I imagine the current requirements are minimal, right? So it should work fine from solar panels.
Alternatively, a purely mechanical version could be made from something like a windmill attached to the belt of a van der Graaf generator. Or maybe a waterwheel…
(PS. Has the ‘save my name’ feature in this comment engine ever worked?)
14mL for 3600J, I wouldn’t call this efficient (in a saturated wet environment). You can cool 860mL of water for the same amount of energy, and usually, you need to reach the dew point to get it to condense by itself. Said differently the dehumidifier will perform better, faster and more efficiently.
3600 J will cool 860 mL of water a single degree… and so what?
3600 J is also the amount of heat you need to pump to condense 1.6 mL of water vapour into liquid water, which is a more relevant measure.
By comparison, using ions and an electric field to persuade water droplets to coalesce and yield 14 mL / 3600 J is doing pretty well. But it requires that the water droplets (fog) already exists — nature has already done most of the thermodynamic work.
Fog is already liquid water – it should take a fraction of the energy to collect because no phase transition is needed.
Did you not make it to the third paragraph before deciding you must immediately comment?
Yes.
The heat of vaporization of 14 ml of water is about 32 kJ so they’re using about 10% of what would be needed to condense the water from vapor, but simply collecting the water from fog shouldn’t take even 1%.
In fact it should take almost no energy at all. People in desert climates where night fog commonly occurs use completely passive canvas nets to collect water, getting around 100-500 ml per square meter of netting per day. Compared to that, this is just a terrible waste of energy.
OK, agreed there: collection of water droplets should take an even smaller fraction of the energy of the phase transition than this scheme does.
Making ions is hard work. Whether to accelerate rocket exhaust or move water droplets, it’s input energy you usually don’t get back, except as waste heat (or perhaps as stored chemical energy).
I would suggest that a simple fan sucking in air through a wire mesh would be more energy efficient. That’s what the ionizing device is doing – moving air, but not very efficiently.
The issue with the canvas nets is that they’re pretty big and not portable, since they can’t be too densely woven or the wind won’t pass through them. Being large and subject to airflow, a lot of the water evaporates away before it wicks down and drops into the collection through, or the wind sprays it around and it misses the collector. That’s why the net can only collect about 10% of the fog that passes through.
No Dude, the issue is that without charge the fog mostly doesn’t impact the mesh unless it’s got electrostatic force to cause the droplet to penetrate the air cushion. You don’t need to propel the air fast to make it work, just enough to constantly refresh the available droplets.
You know how you can deflect the water flowing out of a faucet with an electrostatic field? Conceptually, I feel like this isn’t that different except you have to account for these being tiny suspended particles and needing to make them impact something for them to adhere to and not just float away. I don’t think centrifuging the air would be efficient enough, but I guess I could be wrong. I think things may have been done with wicking and such, but a sparse wire mesh can allow much more flow and capturing for the resistance, and everything drips right off.
I’m not sure if it might work for the droplets, instead of being discharged into the mesh, to be insulated from it and then drop under their own weight while still charged. And/or, do some kind of kelvin water dropper shenanigans to waste less energy.
Aka. the mesh isn’t dense enough. They could employ multiple layers to force the droplets to impact something, but the more you occlude the path, the more air resistance you get and the wind will simply go around the fog collector.
The ionizing device simply forces air flow, which makes the droplets hit something. It’s not strong enough to literally pull the droplets onto the surface. A regular fan would be more efficient in this role.
The usual demo has more to do with the Coanda effect, where fluid flows tend to follow a curved surface. The electrostatic field deflects the water a little at some distance, but when you bring the glass rod closer to the stream of water, you constrict the availability of air in the gap between the rod and the water, and this is what bends the stream of water strongly in the direction of the rod.
A lot of physics teachers use this wrongly to show how “strong” the electrostatic effect is, but they’re really showing off a pneumatic effect rather than an electrostatic effect.
Yeah, no. Watch the video again, the fog in the first test is very clearly being pushed past the mesh by something when unpowered, yet the density before and after passing the mesh is basically unchanged. Once power is applied, the velocity does increase some but the input density reduces, presumably because it’s still supplied by the same fog maker with a limited output. And for most of the length of the device, very little fog appears to get past the mesh. While in a real fogbank, higher velocity would mean interacting with more fog particles and increasing your collection rate, a sparse mesh like this probably wouldn’t go from letting most of the fog pass straight through to suddenly interacting with most of the particles one centimeter away just because there was slightly more airflow. It’s got to be the voltage doing it.
Also… no, I have bent the water stream without getting that close to it. Do it yourself if you want, build a water dropper or something. It’d be even more if you had both effects going, but the electrostatic one is still entertaining enough to me. And remember, electrostatics is also enough to make hair stand on end even without any fluid physics going on.
Hydrogen burning steam turbine is the way to go…
Heheh so what stake are you personally holding in hydrogen
None, we would just make it from the free water, that comes off of, and powers, David’s waterwheel, if it were hooked up to a generator.
I think that’s what they call a circular economy.
hum… 14 mL/Wh with a “strong fog”. That would be about 1.4L/h on a 100W solar panel for example, again depending on this “strong fog”, which I doubt you’ll be seeing anywhere in a desert. I think a 100W solar panel would be more useful pumping water from a well in this case.
a surprising number of deserts in the world have lots of fog despite having almost no rain, and an equally surprising number of people live in or near them. The Atacama desert in chile is perhaps the most famous, but parts of the sahara get plenty of fog as well.
Sure, you can sink a well and hit usable water if you’re lucky, but since there’s no rain, there’s only so much groundwater pumping people can do before the aquifer is depleted.
And how well does a solar panel work when it’s foggy anyway?
My kneejerk reaction as well, but then I remembered rechargeable batteries are a thing.
righto, doubling your capital expense.
The fog only occurs during the morning, then it’s sunny and hot all day. So it charges during the day, and creates water at night.
…If it’s that foggy, you do not need to condense moisture from the air to have water. You will find it available in large quantities nearby.
It would seem that way. However, tell that to Namibia. Fog belts extending 30km inland from the sea every day. No water in sight. Lots of fog does not equate to liquid water source nearby.
Drilling is quite expensive and in the desert you first have to transport all drilling equipment and most probably have to drill deep, guessing between 150-250 meters (500 to 800 feet) to find water, possibly more. Pumping water hundreds of meeters is also not an easy task. And when done, after some years of extensive use you will lower the ground water level.
I think the point of this idea is the simplicity, add a small fan do get a lot of air passing by to condence water might increase the efficiency.
Seems for that expense, you could just set up a much larger expanse of mylar for dew to form on, and collect a comparable rate passively. Especially if you are assuming extremely-high humidity… The main advantage here seems to be compactness
Compared it to a thermoelectric peltier dehumidifier, about the least energy efficient way to make cold for dehumidification. This is obviously a different pathway, but it would be good to see how this stacks up to compressor based dehumidifiers in more real world conditions.
Will it be cheaper than just trucking water in”
With a solar panel, let’s say 100W and 14 hours of sunlight per day. That 14 mL/W collection rate, if it truly could be sustained, is 19.6L a day. That is potentially enough for primitive household use for a single person or frugal couple.
If you’re living in an arid place or otherwise are unable to setup a well, then living on minimal water usage is probably already assumed. An extra 20L/day is a luxury from air and sunlight for the cost of some electronics, mesh, and a decent sized solar panel is a bargain. Save your money for trucking out the liquid, specifically the honeywagon that an off-grid home periodically needs.
Extending this to Hawaiians, where some rural properties don’t have a viable groundwater source and people have long used elaborate rainwater collection as their primary water source or to supplement their water supply.
The thing is – that 14l is from saturated air. The lower your humidity level the lower your yield per unit of time is going to be.
What you can collect in 1 hour from a jungle on the edge of a sea is very different than in an arid area.
For those HI – there are already commercial systems that do this readily available.
That 14ml rate is an assumption based on pea-soup fog, which would never exist in an area where it would be viable to truck around water (or build big solar condensation plants).
Interesting case with rural Hawaii, but as you say it’s more likely to rain a lot of the time and you can collect that a lot more cheaply.
The referenced paper says Many remote drought-prone coastal areas have little or no rain and prohibitively expensive water transportation costs but have dense fog that occurs on a regular basis, and references the source, which indicates the “regular basis” is seven times in a year.
What’s enough water to sustain a family for months between fog events, plus some reserve? 3000 liters? And you need to collect that in the hour or so of morning fog that you get.
That 14 mL/Wh suddenly doesn’t look good at all. 3000 L will need 214 kWh of energy. If it’s all collected in one hour during that rare fog event, that’s a 214 kilowatt high voltage generator you need, plus the storage battery to run it.
Seems like an awful lot of expense to collect enough water for a family to survive on.
But even dry desert air contains a few tenths percent water (several grams per cubic meter), which a compressor-based or sorbent-based water extractor can readily capture for you. The energy required is no better than the electrostatic fog collector (a few hundred joules per gram), but you could run it all the time, or purely on solar power a few hours per day. A sorbent-based water separator could even run on waste heat.
I don’t think it undermines your point, but I don’t know why the article cited that particular paper. There are plenty of dry areas elsewhere in morocco where there’s fog quite regularly, if not daily, for a significant part of the year. For example, look up the area where the Dar Si Hmad organization operates.
The thing is, fog collection is a viable option there because not only do they have ample fog, but it can be done passively, without requiring electricity or specialized maintenance.
If you’ve got power and the ability to maintain it, a compressor/sorbent based dehumidifier is undoubtedly a better option in most cases; if you don’t, building a passive collector is surely easier and cheaper unless you’re incredibly space-constrained.
Sometimes I think that people have more a fetisch for making the video rather than making the project.
An awful lot of fast forward to see how it works.
New to youtube and the algorithm are we?
Why say something in 5 minutes that can be alluded to and talked around for 37 minutes followed by a perfect-first-time build montage followed by uncritically declaring success?
Have you heard of ad revenue
I’m sure it could be very successful at extracting money from gullible people
Most eco tech fits that description, unfortunately. It’s not ideal for anybody
The biggest issue that’s glossed over in this entire video is the supply of completely saturated air. Fog doesn’t flow like this, it condenses out of the air. You can’t create a “stream of charged/ionic water molecules” in static fog. Even if you could, you’d be creating a dry barrier between the airmass able to affected by the charged field versus the air mass just outside the range. A better application of that electricity to render water from the air would be a simple peltier unit creating a cold surface for the water to condense on, the same concept but much much lower power and much higher efficiency, though the rate is lower as it’s practically passive. But hey, no need for kJ and kill-you-power.
He specifically showed that wasn’t true by using a peltier dehumidifier for comparison. More traditional dehumidification may very well be a more efficient way to condense dog, but peltier modules are extremely inefficient, especially for cooling.
Peltier’s are crazy inefficient though. Tons of people have tried with them already (and most of the attempts are actually Kickstarter scams).
A heat pump/AC with a fan to push a lot of air across the cooling coils is, literally, the only way to do this in the real world (and all working ‘air-to-water’ systems use this – even if a lot try to hide it).
Air is almost never completely still. Even on a completely “windless” day, the air is still moving at maybe half a meter per second.
I just learned that the moisture vaporators used by farmers on Tatooine aren’t as far fetched as I first thought.
https://starwars.fandom.com/wiki/Tatooine
What I thought of as well. I wonder if having gravity plating and repulsorlifts and stuff makes it easier to condense tiny bits of moisture from the air… Probably
I wonder how well it would work when there is no fog. Water molecules wandering around in the air are polar and would be attracted to one of the two electrodes.
Uncharged water molecules would not be attracted to either electrode, because they don’t carry a net charge. But, being polar they would have a statistical tendency for a fraction of them to rotate and orient in the electric field though.
We know how much energy it takes to condense water out of air. Its a lot. And you need to move a lot of air. Its why large-scale water extraction systems are always basically air conditioners with fans and why its never viable except in very humid places – which aren’t the places short of water.
They may be short of clean water.
You wouldn’t want to drink from an algae filled muddy pool full of crocodiles.
There is no such thing as a free lunch, or free energy, or free water.