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The article claims 3x more efficiency in a confusing sentence: ”Their prototype generates drinking water at a rate of 0.3 liters per hour, and requires only 20

The article claims 3x more efficiency in a confusing sentence: ”Their prototype generates drinking water at a rate of 0.3 liters per hour, and requires only 20 watts of power per liter.” So the unit only produces 0.3 liters an hour but if you wait 3 hours and provide 20 watts of power (7watts/hour), you’ll have a full liter.

qayxc 4y ago
> So the unit only produces 0.3 liters an hour but if you wait 3 hours and provide 20 watts of power (7watts/hour), you’ll have a full liter. That doesn't make any sense. 20W of power draw over 3⅓ hours is ≈67Wh (Watthours, not Watts per hour), so 67Wh per litre (energy use; independent of time) and it takes 3⅓ hours to get this litre of potable water with 20W of power. In other words to get 1 litre in an hour, the device might require ≈67W of power (assuming that kind of perfect scaling is even possible with their design).
- BeefWellington 4y ago
  The wording in the article is specifically: > requires only 20 watts of power per liter. Whether the article is accurate or not I think you missed that.
  - qayxc 4y ago
    The point is that 7W/hour is nonsensical. It's a non-unit and physically doesn't make sense in any context. The power is independent from the volume. Total energy use is volume dependent. 20 Watts per litre is mix of units that's nonsensical. Watt is Joules (Energy) per second (time), i.e. power. Either time is irrelevant, that is the device draws 20 Watts of power, in which case you can ditch the litre. Or the power draw is dependent on the performance in that more power equals higher throughput. Neither case is in any way shape or form correctly described by "20 Watts per litre". Hope that makes it clearer now.
    - BeefWellington 4y ago
      Science reporting is not great but colloquially people use 20W per <job done> as a way of meaning Watt-hours. If this is correct, they're saying it takes 20 watts (meaning Wh) to deliver a Litre of water, over three and a bit hours. The time is provided just obfuscated by their "we deliver 0.3L/hour" statement, so by saying 20W/L it does sort of make sense within the context. ~6W/hour (if it means we use a total of 6Wh) would be different than claiming the system runs off 0.1 Watts. Given the size of that solar panel, I suspect they're claiming they are using ~6 Watts for a period of one hour to produce 0.3L. Alternately, they're just flat out wrong and they're using 20 watts for one hour to produce 0.3L. It could be worded better but I think this is what they're trying to say is that they're consuming 6W.
      - qayxc 4y ago
        > Science reporting is not great but colloquially people use 20W per <job done> as a way of meaning Watt-hours. After watching the video I can confirm that it's actually 20Wh/l for 0.3l/h and 15Wh/l at 1l/h (I'm a bit puzzled how that works, but hey - that's what the inventor says). > It could be worded better but I think this is what they're trying to say is that they're consuming 6W. I would be happy if they'd manage to simply repeat what was said in the video. This is the official MIT news portal after all and I would expect it to be run by people smart enough to use the correct units, but alas...

qayxc 4y ago

> So the unit only produces 0.3 liters an hour but if you wait 3 hours and provide 20 watts of power (7watts/hour), you’ll have a full liter. That doesn't make any sense. 20W of power draw over 3⅓ hours is ≈67Wh (Watthours, not Watts per hour), so 67Wh per litre (energy use; independent of time) and it takes 3⅓ hours to get this litre of potable water with 20W of power. In other words to get 1 litre in an hour, the device might require ≈67W of power (assuming that kind of perfect scaling is even possible with their design).

BeefWellington 4y ago
The wording in the article is specifically: > requires only 20 watts of power per liter. Whether the article is accurate or not I think you missed that.
- qayxc 4y ago
  The point is that 7W/hour is nonsensical. It's a non-unit and physically doesn't make sense in any context. The power is independent from the volume. Total energy use is volume dependent. 20 Watts per litre is mix of units that's nonsensical. Watt is Joules (Energy) per second (time), i.e. power. Either time is irrelevant, that is the device draws 20 Watts of power, in which case you can ditch the litre. Or the power draw is dependent on the performance in that more power equals higher throughput. Neither case is in any way shape or form correctly described by "20 Watts per litre". Hope that makes it clearer now.
  - BeefWellington 4y ago
    Science reporting is not great but colloquially people use 20W per <job done> as a way of meaning Watt-hours. If this is correct, they're saying it takes 20 watts (meaning Wh) to deliver a Litre of water, over three and a bit hours. The time is provided just obfuscated by their "we deliver 0.3L/hour" statement, so by saying 20W/L it does sort of make sense within the context. ~6W/hour (if it means we use a total of 6Wh) would be different than claiming the system runs off 0.1 Watts. Given the size of that solar panel, I suspect they're claiming they are using ~6 Watts for a period of one hour to produce 0.3L. Alternately, they're just flat out wrong and they're using 20 watts for one hour to produce 0.3L. It could be worded better but I think this is what they're trying to say is that they're consuming 6W.
    - qayxc 4y ago
      > Science reporting is not great but colloquially people use 20W per <job done> as a way of meaning Watt-hours. After watching the video I can confirm that it's actually 20Wh/l for 0.3l/h and 15Wh/l at 1l/h (I'm a bit puzzled how that works, but hey - that's what the inventor says). > It could be worded better but I think this is what they're trying to say is that they're consuming 6W. I would be happy if they'd manage to simply repeat what was said in the video. This is the official MIT news portal after all and I would expect it to be run by people smart enough to use the correct units, but alas...