Comment by mcpackieh | Hacker News Reader

Comment by mcpackieh | Hacker News Reader

"Cheaper than tap water" is an inane meaningless claim. Cheaper than tap water where? Tap water isn't one price, the price of fresh water is hyper local. I doubt this technology will make water cheaper even for most people living along a coast.

> From these tests, the researchers calculated that if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour

So 1) They haven't yet tried this at the scale of one square meter. So this is a lab project that is nowhere close to commercialization but that doesn't stop them from making grand vague pronouncements about its potential. Classic MIT tbqh.

2) 5 liters per square meter per hour is trash. An average American uses a bit more than 300 liters of water a day, so you need 60 square meters of this to support one average American. So you'd need more than 5000 square kilometers of this to provide water to NYC. Does this sound like it's going to be cheaper than the tap water they already have?

> 5 liters per square meter per hour is trash. An average American uses a bit more than 300 liters of water a day, so you need 60 square meters of this to support one average American.

Unit check. 5 liters per hour is 120 liters per day. So you need 2.5 m^2 per American (ignoring whether the hourly rate is sustainable, just correcting units).

This is about a third of the projected area of a typical car, so in terms of surface-area-per-person we're at about half that of cars (given about 2/3 of a car per American).

Good catch.

you can only account for 6hrs of sun per day, so it's more like 30liters per day. that gives you 10m^2 per American. however serving Americans is not a practical use case. i agree these kinds of systems are not going to be competitive with large scale PV driven RO (i build medium scale solar RO plants in africa and they're pretty good and surprisingly affordable). however having a mobile one you can put on a vehicle or deploy in a small scale distributed manner with little to no expertise would be extremely useful in low population density or nomadic context.

I guess one problem is that by definition, sea water is at sea level, and any desalinated water would have to be pumped to deliver it anywhere. Pumping costs. By contrast, isn't most fresh water delivered by gravity, for free?

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