Well… There would also have to be water to actually collect from the air. Thunderfoot made a really good video about these dehumidifiers when yet another one popped up on Kickstarter claiming to end water shortages.
Well… There would also have to be water to actually collect from the air. Thunderfoot made a really good video about these dehumidifiers when yet another one popped up on Kickstarter claiming to end water shortages.
Hi_ImSomeone@lemmy.world 3 weeks ago
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.