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You’re asking the right questions. I’d like to understand the conservation of energy angle on this.

You usually have to expend energy to get water out of the air, no?

Absolutely yes. Dehumidification typically involves a full refrigeration cycle. It's like leaving a refrigerator running with the doors wide open, the only purpose being to drain out the few drops of water that drip off the condenser coil every minute. Not a very productive process.

And any process which provides energy-free dehumification would also have the secondary (or primary) benefit of providing energy-free freshwater.

I'd imagine they've thought of both the above applications, and their protein nanowires aren't suitable.

An old scout trick to get water out of the air is to use a plastic sheet to make a "solar still", moisture condenses on the underside of the sheet and is collected in a cup. The environment provides the energy and moisture.

That is a cool trick, but in that case the energy gradient is from inside to outside the sheet (sunlight heats the air under the sheet), right?

I'm sure the researchers have thought of this, but it wasn't in the abstract.

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