4 ms·

So crazy question: take a dehumidifier, attach some solar panels, and deploy at scale for non-potable water suitable for crop irrigation anywhere that isn't a d

So crazy question: take a dehumidifier, attach some solar panels, and deploy at scale for non-potable water suitable for crop irrigation anywhere that isn't a desert. Does it work? And if not, why?

casey2 4mo ago
What do you mean work? No, because there is no single dehumidifier on the market that will get you enough water, so you are out $80 grand, you could have just paid for water delivery.
mrguyorama 4mo ago
It "works" in the sense that this is what 99% of "Get water from air" scams are. The reason it doesn't actually work is that it is extremely inefficient. Getting water to condense requires you to somehow reject massive quantities of heat. That's fundamental to physics. Also, literally anywhere a dehumidifier is reasonably effective, is humid and usually doesn't have such dire water problems. Deserts have extremely low humidity and dehumidifiers working in a desert will produce very little water. Even a good humidifier in a humid environment is burning KW to generate on the order of ten liters of water a day. There are a couple places on earth that are essentially deserts but have an early morning humid fog roll through regularly, and those places figured out capturing that water in the air long long before we invented the refrigeration cycle. It is literally cheaper to desalinate. Maybe you could build giant greenhouses to fill with sea water and let the sun evaporate the water and collect that with a dehumidifier? Still absurdly inefficient. Water has such an obscene specific capacity for heat that any thermal avenue of separating it from something else will use immense energy.
LarsAlereon 4mo ago
It takes too much energy and produces water too slowly to scale. In general any area with sufficient moisture in the air to explore this also has easier access to rain and ground water.
- LogicFailsMe 4mo ago
  Great point, in my case in the PNW, the water from my local well is infested with manganese (as in clogging the household plumbing in the absence of a sediment filter) and other contaminants and the water company providing it is owned by private equity. Legally, I can drill my own well for non-potable irrigation, but god forbid I filter and/or chlorinate it for my own household use. So I end up considering options like this, thanks for debunking.
  - SoftTalker 4mo ago
    You don't need to chlorinate water from your own well, unless maybe you have a cistern that you are filling for storage. And who's going to know if you are drinking it or watering your garden?
    - LogicFailsMe 4mo ago
      At the very least I would UV disinfect anything coming from the ground and absolutely make use of a 20 micron sediment filter if only to address cognitive load: Another place, another time, coliform bacteria from the well. Super fun(not).
      - picofarad 4mo ago
        I vacillate between trusting my well and trusting my RO (10,5,1 micron filters, plus the membrane). But it isn't healthy to drink RO all the time and I don't wanna mess with remineralization. My well is 100' and 13 years old.
        SoftTalker 4mo ago
        For me I'd do a sediment filter and a charcoal filter and call it good. Send a sample out for analysis a few times a year.
- jillesvangurp 4mo ago
  A lot of energy is only a problem if that energy is very expensive. The good news in a desert: plenty of sunshine. So you can generate a lot of electricity with some cheap solar panels, there is plenty of space to put some down, and there aren't a lot of NIMBYs around to complicate the permitting process for that. Some desert ecosystems actually depend on condensation with specialized plants and animals harvesting humidity from ocean breeze. Large parts of e.g. the Sahara border on the Atlantic ocean. Lots of water in the air but not a lot of rain. And even if humidity is low, there still is some water in the air usually. But the simple fact of course is that there is a lot more water in water than there is in air. If you want to extract meaningful amounts of water from air, you need to process a lot of it.
wagwang 4mo ago
The humid areas where they might work probably already have a lot of water?
oceanplexian 4mo ago
The short answer is all those problems have already been solved. Israel desalinates 75-85% of its drinking water. The problem is political and economic dysfunction. California for example could be doing widespread desalination with nuclear power and technology from the 1970s. They could also greatly expand reservoirs and waterways, but don’t do it. Very similar to Rome in the 400s, when people were using aqueducts built by a past civilization but lost the ability to construct them.
- iso1631 4mo ago
  Nuclear is very expensive per MWh and thus per litre of water generated Solar on the other hand is very cheap, and you don't need to desalinate 24/7 -- just do it when power is cheapest (which is during the sunny times if you have large amounts of solar, during windy if you have large amounts of wind, etc)
KaiserPro 4mo ago
Yield depends on humidity, which varies according to region and season. It also requires more infrastructure to get yield. In theory all you'd need to have is these etched metal plates, a transparent dome and a source of briny water. (and a cleaning mechanism) The etched plates creates 100% humidity (probably more as it'll condense out)

So crazy question: take a dehumidifier, attach some solar panels, and deploy at scale for non-potable water suitable for crop irrigation anywhere that isn't a desert. Does it work? And if not, why?

casey2 4mo ago

What do you mean work? No, because there is no single dehumidifier on the market that will get you enough water, so you are out $80 grand, you could have just paid for water delivery.

mrguyorama 4mo ago

It "works" in the sense that this is what 99% of "Get water from air" scams are. The reason it doesn't actually work is that it is extremely inefficient. Getting water to condense requires you to somehow reject massive quantities of heat. That's fundamental to physics. Also, literally anywhere a dehumidifier is reasonably effective, is humid and usually doesn't have such dire water problems. Deserts have extremely low humidity and dehumidifiers working in a desert will produce very little water. Even a good humidifier in a humid environment is burning KW to generate on the order of ten liters of water a day. There are a couple places on earth that are essentially deserts but have an early morning humid fog roll through regularly, and those places figured out capturing that water in the air long long before we invented the refrigeration cycle. It is literally cheaper to desalinate. Maybe you could build giant greenhouses to fill with sea water and let the sun evaporate the water and collect that with a dehumidifier? Still absurdly inefficient. Water has such an obscene specific capacity for heat that any thermal avenue of separating it from something else will use immense energy.

LarsAlereon 4mo ago

It takes too much energy and produces water too slowly to scale. In general any area with sufficient moisture in the air to explore this also has easier access to rain and ground water.

LogicFailsMe 4mo ago
Great point, in my case in the PNW, the water from my local well is infested with manganese (as in clogging the household plumbing in the absence of a sediment filter) and other contaminants and the water company providing it is owned by private equity. Legally, I can drill my own well for non-potable irrigation, but god forbid I filter and/or chlorinate it for my own household use. So I end up considering options like this, thanks for debunking.
- SoftTalker 4mo ago
  You don't need to chlorinate water from your own well, unless maybe you have a cistern that you are filling for storage. And who's going to know if you are drinking it or watering your garden?
  - LogicFailsMe 4mo ago
    At the very least I would UV disinfect anything coming from the ground and absolutely make use of a 20 micron sediment filter if only to address cognitive load: Another place, another time, coliform bacteria from the well. Super fun(not).
    - picofarad 4mo ago
      I vacillate between trusting my well and trusting my RO (10,5,1 micron filters, plus the membrane). But it isn't healthy to drink RO all the time and I don't wanna mess with remineralization. My well is 100' and 13 years old.
      - SoftTalker 4mo ago
        For me I'd do a sediment filter and a charcoal filter and call it good. Send a sample out for analysis a few times a year.
jillesvangurp 4mo ago
A lot of energy is only a problem if that energy is very expensive. The good news in a desert: plenty of sunshine. So you can generate a lot of electricity with some cheap solar panels, there is plenty of space to put some down, and there aren't a lot of NIMBYs around to complicate the permitting process for that. Some desert ecosystems actually depend on condensation with specialized plants and animals harvesting humidity from ocean breeze. Large parts of e.g. the Sahara border on the Atlantic ocean. Lots of water in the air but not a lot of rain. And even if humidity is low, there still is some water in the air usually. But the simple fact of course is that there is a lot more water in water than there is in air. If you want to extract meaningful amounts of water from air, you need to process a lot of it.

wagwang 4mo ago

The humid areas where they might work probably already have a lot of water?

oceanplexian 4mo ago

The short answer is all those problems have already been solved. Israel desalinates 75-85% of its drinking water. The problem is political and economic dysfunction. California for example could be doing widespread desalination with nuclear power and technology from the 1970s. They could also greatly expand reservoirs and waterways, but don’t do it. Very similar to Rome in the 400s, when people were using aqueducts built by a past civilization but lost the ability to construct them.

iso1631 4mo ago
Nuclear is very expensive per MWh and thus per litre of water generated Solar on the other hand is very cheap, and you don't need to desalinate 24/7 -- just do it when power is cheapest (which is during the sunny times if you have large amounts of solar, during windy if you have large amounts of wind, etc)

KaiserPro 4mo ago

Yield depends on humidity, which varies according to region and season. It also requires more infrastructure to get yield. In theory all you'd need to have is these etched metal plates, a transparent dome and a source of briny water. (and a cleaning mechanism) The etched plates creates 100% humidity (probably more as it'll condense out)