9 ms·

Edit: I wrote out the comment below criticizing the efficiency of this device, when compared to reverse osmosis RO desalination (100x less efficient). However,

Edit: I wrote out the comment below criticizing the efficiency of this device, when compared to reverse osmosis RO desalination (100x less efficient). However, they’re not trying to be more efficient than RO devices, they’re trying to be more compact, portable, and avoid the need for filters. They’re solving for a different problem than I was measuring them against. In my race to criticize, I overlooked those key details. I still think my comment is worth reading to learn about the efficiency differences but I guess that measurement is not important for the viability of this technology. Original criticism below: ——————— I’m skeptical about how practical this actually is. While it’s refreshing to see a drinking water solution that isn’t based on inefficient dehumidifier technology, this still seems impractical. From the demonstration video, their portable ~50 watt solar panel took 30 minutes to get a few ounces of drinking water. It looked like a cold winter day, so let’s be generous and assume the panel only produced 15 watts of power during those 30 minutes. Let’s also be generous and say they got 5 ounces of water. That means they produce 1 ounce of water for every 3 watts. That’d be 333 ounces per kWh. To put that into perspective, a desalination plant produces more than 100x that much. Yes, there is lots of additional infrastructure to consider with a traditional desalination plant but It’s not like this solution wouldn’t require the same complexity to scale up. I don’t remember the cost of dehumidifier drinking water “solutions” but I think this is slightly more efficient than those horrifically inefficient solutions.

tomxor 4y ago
From the article it sounds like they are looking for ways to scale down (i.e small portable units are the target form factor, not a mere demo), and this is where it compares favourably against things like reverse osmosis for efficiency.
- MichaelApproved 4y ago
  I was so quick to criticize technology that I completely overlooked those points. Reading the article again, it’s embarrassing to see that I missed it when they were emphasizing it so much. I have one more lingering criticism that I don’t think they addressed (I reread it twice). What happens to the salt after it’s removed? If they don’t have a filter, where does it go? Do they pump brine water back?
  - QuikAccount 4y ago
    You can pump brine water back but if I recall you can't just dump it all back at once because it's so highly concentrated. Ideally you would be able to find an alternate use for it.
    - MichaelApproved 4y ago
      For these small amounts, I doubt pumping it back out would be an issue but is that what they’re doing? I thought the metal plates were collecting the salt but the article and video don’t make it clear.
      - nullc 4y ago
        In CEDI at least the ions are trapped in a resin then are driven across a membrane by a charge, on the other side of the membrane you run water to flush them out. Some comment in the article left me thinking they end up trapping them in the media and have to reverse charge to release them so I assume it would operate pulsed and presumably have a valve to dump the output during regen. Though I'm a little confused in that normally CEDI is used after RO because the CEDI media is pretty sensitive to fouling and also doesn't work well when the water conductivity is highly variable. Maybe they solve the fouling with charge reversal. ...who knows, because popular coverage of this stuff never hits on the important parts and almost never links the relevant publications. There are many ways to make drinkable water from seawater-- making them some useful mixture of energy efficient, cost effective, portable, waste-water efficient, and reliable is the actual hard part.
      - bruce511 4y ago
        given the size of the thing it's likely to be positioned very close to the water source, so I expect it just dumps it outside the device. I mean, if I was running it on a boat, or next to the sea, I'd just basically pour the waste out right next to the device. And I agree, at ounces per hour there's no need to dilute the brine, just dumping it is fine.
  - tomxor 4y ago
    Note that they are not merely aiming for portability, but efficient portability. This particular passage is suggestive of their device being more efficient than RO at small scales, although no figures are given for comparison: > Commercially available portable desalination units typically require high-pressure pumps to push water through filters, which are very difficult to miniaturize without compromising the energy-efficiency of the device, explains Yoon.
electroly 4y ago
FWIW, I think you made a minor math error; you lost track of the 30 minutes. It would be 1 ounce of water for 3 watts of power over 30 minutes, which is 1.5 Wh of energy. That's 666 ounces per kWh.
- MichaelApproved 4y ago
  It wouldn’t be the first time I made a mistake like that by not clearly identifying my units but I think I got it right. Let me rephrase and use watt/hour units. I was assuming it was a 50 watt panel that would only produce 30wh from the weak winter sunlight. Divide 30wh by two (since it was only ru Ning for half an hour) and get 15 watts generated to purify 5 ounces. Had they let it run for the full hour, they’d get 10 ounces from my assumed 30wh of energy the panel produced. 30wh divided by 10 ounces would be 3wh per ounce (or unit of water produced). How many units of water can be produced by 1kwh? Let’s divide 1,000wh by 3wh to get the result of 333.3 units (ounces) produced.
  - electroly 4y ago
    Wh is a measurement of energy, but W is a measurement of power (that is, the rate of energy). They are different units of measurement and you're mixing them up here. Here, you've doubled the original rating of 15 watts up to 30 watts; that's the result of the confusion between energy and power. You don't divide the wattage in half when you run it for half the time, nor double it when you run it for twice the time; that's not how power works. That's how energy works. In your original post, the number was 15 watts, and you figured it produced 5 ounces of water in 30 minutes. So you then figured that 3 watts can produce 1 ounce of water in 30 minutes. So far so good; that's correct. If the panel continuously produces 3 watts of power (remember: watts are a rate of energy) over a period of one hour, that's 3 watt-hours of energy. For 30 minutes, it's 1.5 watt-hours of energy. Thus, it took 1.5 watt-hours of energy to produce 1 ounce of water. (1000 watt-hours) * (1 ounce / 1.5 watt-hours) = 666 ounces. It may make more sense to translate this into distance, which I think is more intuitive for most people. Watts (power) are like miles-per-hour (velocity), and watt-hours (energy) are like miles (position). The panel runs at 15 MPH. After 30 minutes it has run 7.5 miles and produced 5 ounces of water. Thus, it could produce 1 ounce of water by running just 1.5 miles. It still runs at a speed of 15 MPH no matter what.
dfsdf4sds 4y ago
I want to thank you for your edit, and for keeping the original text. Recognizing something you said ignored portions of the argument, changing the argument, and keeping the original portion to show _why_ you were wrong but still adds to the conversation is very valuable. I commend you for your ability to double guess yourself
- MichaelApproved 4y ago
  Thank you. And you’re right, I am amazing ;) But seriously the main reason I write these comments is to work through my thoughts as I try to articulate them and get feedback on what I’m thinking. I’m actually happy when someone points out a mistake because I learned something. When I’m right, I haven’t gained anything. Sure, my ego enjoys the satisfaction of being right but my already inflated ego doesn’t need anymore stroking.
  - bombcar 4y ago
    Heh sounds like what Socrates said - it’s better to be corrected than to be correct.
    - antisthenes 4y ago
      It's even better to be correct after being corrected by yourself.
  - Damogran6 4y ago
    My biggest issue is when I hit send on something when what it really needed was another editorial revision.
    - MichaelApproved 4y ago
      I almost instantly hit the edit button after I post a comment.
scoopertrooper 4y ago
The article says they can get 1 liter for every 20 watts. So that'd give them 17,597 ounces per kWh.
- denton-scratch 4y ago
  It does say that; and you've converted between watts and watt-hours. The article's claim doesn't make sense.
  - deleted 4y ago
    [deleted]
  - SamBam 4y ago
    I feel like nobody watched the video (although I do wish the article text had been clearer). The video specifically shows (at 1:34) that the machine operates at 15Wh/L (for the larger version, the smaller version is 20Wh/L). This is 15Wh/33 oz (since we seem so set on using customary units), or 2200 oz per kWh.
    - denton-scratch 4y ago
      I didn't; I don't generally follow video links, unless I deliberately went looking for a video. Specifically, I don't follow many video links from HN; I treat HN as a text/plain site. So my remarks were only about the article text.
SamBam 4y ago
The video claims that the machine operates at 15Wh/L (for the larger version, the smaller version is 20Wh/L). This is 15Wh/33 oz, or 2200 oz per kWh. That's roughly one order of magnitude greater than your estimate.

tomxor 4y ago

From the article it sounds like they are looking for ways to scale down (i.e small portable units are the target form factor, not a mere demo), and this is where it compares favourably against things like reverse osmosis for efficiency.

MichaelApproved 4y ago
I was so quick to criticize technology that I completely overlooked those points. Reading the article again, it’s embarrassing to see that I missed it when they were emphasizing it so much. I have one more lingering criticism that I don’t think they addressed (I reread it twice). What happens to the salt after it’s removed? If they don’t have a filter, where does it go? Do they pump brine water back?
- QuikAccount 4y ago
  You can pump brine water back but if I recall you can't just dump it all back at once because it's so highly concentrated. Ideally you would be able to find an alternate use for it.
  - MichaelApproved 4y ago
    For these small amounts, I doubt pumping it back out would be an issue but is that what they’re doing? I thought the metal plates were collecting the salt but the article and video don’t make it clear.
    - nullc 4y ago
      In CEDI at least the ions are trapped in a resin then are driven across a membrane by a charge, on the other side of the membrane you run water to flush them out. Some comment in the article left me thinking they end up trapping them in the media and have to reverse charge to release them so I assume it would operate pulsed and presumably have a valve to dump the output during regen. Though I'm a little confused in that normally CEDI is used after RO because the CEDI media is pretty sensitive to fouling and also doesn't work well when the water conductivity is highly variable. Maybe they solve the fouling with charge reversal. ...who knows, because popular coverage of this stuff never hits on the important parts and almost never links the relevant publications. There are many ways to make drinkable water from seawater-- making them some useful mixture of energy efficient, cost effective, portable, waste-water efficient, and reliable is the actual hard part.
    - bruce511 4y ago
      given the size of the thing it's likely to be positioned very close to the water source, so I expect it just dumps it outside the device. I mean, if I was running it on a boat, or next to the sea, I'd just basically pour the waste out right next to the device. And I agree, at ounces per hour there's no need to dilute the brine, just dumping it is fine.
- tomxor 4y ago
  Note that they are not merely aiming for portability, but efficient portability. This particular passage is suggestive of their device being more efficient than RO at small scales, although no figures are given for comparison: > Commercially available portable desalination units typically require high-pressure pumps to push water through filters, which are very difficult to miniaturize without compromising the energy-efficiency of the device, explains Yoon.

electroly 4y ago

FWIW, I think you made a minor math error; you lost track of the 30 minutes. It would be 1 ounce of water for 3 watts of power over 30 minutes, which is 1.5 Wh of energy. That's 666 ounces per kWh.

MichaelApproved 4y ago
It wouldn’t be the first time I made a mistake like that by not clearly identifying my units but I think I got it right. Let me rephrase and use watt/hour units. I was assuming it was a 50 watt panel that would only produce 30wh from the weak winter sunlight. Divide 30wh by two (since it was only ru Ning for half an hour) and get 15 watts generated to purify 5 ounces. Had they let it run for the full hour, they’d get 10 ounces from my assumed 30wh of energy the panel produced. 30wh divided by 10 ounces would be 3wh per ounce (or unit of water produced). How many units of water can be produced by 1kwh? Let’s divide 1,000wh by 3wh to get the result of 333.3 units (ounces) produced.
- electroly 4y ago
  Wh is a measurement of energy, but W is a measurement of power (that is, the rate of energy). They are different units of measurement and you're mixing them up here. Here, you've doubled the original rating of 15 watts up to 30 watts; that's the result of the confusion between energy and power. You don't divide the wattage in half when you run it for half the time, nor double it when you run it for twice the time; that's not how power works. That's how energy works. In your original post, the number was 15 watts, and you figured it produced 5 ounces of water in 30 minutes. So you then figured that 3 watts can produce 1 ounce of water in 30 minutes. So far so good; that's correct. If the panel continuously produces 3 watts of power (remember: watts are a rate of energy) over a period of one hour, that's 3 watt-hours of energy. For 30 minutes, it's 1.5 watt-hours of energy. Thus, it took 1.5 watt-hours of energy to produce 1 ounce of water. (1000 watt-hours) * (1 ounce / 1.5 watt-hours) = 666 ounces. It may make more sense to translate this into distance, which I think is more intuitive for most people. Watts (power) are like miles-per-hour (velocity), and watt-hours (energy) are like miles (position). The panel runs at 15 MPH. After 30 minutes it has run 7.5 miles and produced 5 ounces of water. Thus, it could produce 1 ounce of water by running just 1.5 miles. It still runs at a speed of 15 MPH no matter what.

dfsdf4sds 4y ago

I want to thank you for your edit, and for keeping the original text. Recognizing something you said ignored portions of the argument, changing the argument, and keeping the original portion to show _why_ you were wrong but still adds to the conversation is very valuable. I commend you for your ability to double guess yourself

MichaelApproved 4y ago
Thank you. And you’re right, I am amazing ;) But seriously the main reason I write these comments is to work through my thoughts as I try to articulate them and get feedback on what I’m thinking. I’m actually happy when someone points out a mistake because I learned something. When I’m right, I haven’t gained anything. Sure, my ego enjoys the satisfaction of being right but my already inflated ego doesn’t need anymore stroking.
- bombcar 4y ago
  Heh sounds like what Socrates said - it’s better to be corrected than to be correct.
  - antisthenes 4y ago
    It's even better to be correct after being corrected by yourself.
- Damogran6 4y ago
  My biggest issue is when I hit send on something when what it really needed was another editorial revision.
  - MichaelApproved 4y ago
    I almost instantly hit the edit button after I post a comment.

scoopertrooper 4y ago

The article says they can get 1 liter for every 20 watts. So that'd give them 17,597 ounces per kWh.

denton-scratch 4y ago
It does say that; and you've converted between watts and watt-hours. The article's claim doesn't make sense.
- deleted 4y ago
  [deleted]
- SamBam 4y ago
  I feel like nobody watched the video (although I do wish the article text had been clearer). The video specifically shows (at 1:34) that the machine operates at 15Wh/L (for the larger version, the smaller version is 20Wh/L). This is 15Wh/33 oz (since we seem so set on using customary units), or 2200 oz per kWh.
  - denton-scratch 4y ago
    I didn't; I don't generally follow video links, unless I deliberately went looking for a video. Specifically, I don't follow many video links from HN; I treat HN as a text/plain site. So my remarks were only about the article text.

SamBam 4y ago

The video claims that the machine operates at 15Wh/L (for the larger version, the smaller version is 20Wh/L). This is 15Wh/33 oz, or 2200 oz per kWh. That's roughly one order of magnitude greater than your estimate.