[flukus]

> What makes you so confident that they are using a Peltier?

The article contains a link to an older one and says the device is based on that: http://news.mit.edu/2017/MOF-device-harvests-fresh-water-fro... . Notice the heat sink? Notice quotes like:

In fact, the system doesn’t even require sunlight — all it needs is some source of heat, which could even be a wood fire. “There are a lot of places where there is biomass available to burn and where water is scarce,” Rao says.

That sure sounds and looks like a peltier device to me. MIT is gaining a reputation for crackpot stuff like this.

[nkurz]

Yes, there are previous devices that use a Peltier cooler to condense water directly out of the air. The article you link mentions these as a contrast to what this device is doing: "Another method of obtaining water in dry regions is called dew harvesting, in which a surface is chilled so that water will condense on it, as it does on the outside of a cold glass on a hot summer day, but it “is extremely energy intensive” to keep the surface cool, she says, and even then the method may not work at a relative humidity lower than about 50 percent. The new system does not have these limitations."

This approach uses a "sorbent" that adsorbs water at night, and then then uses sunlight to generate heat to drive the water out of the sorbent during the day. It does not use a thermoelectric cooler: 'The new system, by contrast, is “completely passive — all you need is sunlight,” with no need for an outside energy supply and no moving parts.' Rather than requiring active cooling, this approach requires heat to release free the water from the sorbent. The passive heat sink is used to help capture the water after the heat from the sunlight forces it out of the sorbent: "The desorbed vapour is condensed on a condenser and the heat of condensation is rejected to the ambient by a heat pipe heat sink."

So as best as I can tell, your theory that the paper (which you haven't read) is simply lying about what they are doing? Not impossible, but I think it would require some greater level of evidence the "Notice the heat sink". And while we're at it, how does "biomass available to burn" imply that they are using a thermoelectric aka Peltier cooler? https://en.wikipedia.org/wiki/Thermoelectric_effect

(Yes, I agree that it would be nice if the press release would actually link to the paper that correctly describes the apparatus, but its regrettable failure to do so does not give license to make up your own details as to how it works.)

[extrapickles]

The technique described sounds similar to how desiccant dehumidifiers work, where you capture moisture in a desiccant then remove the moisture by heating the desiccant. The energy required is similar to the chiller based technology due to the laws of thermodynamics.

I have a one that has a descant drum, and it slowly rotates as it blows air through it. A small section of the drum is heated to release water into a separate air stream and that air is then ran through a radiator to cool it, releasing water into a storage container. It costs $0.5-1/L to generate water with it, since the heat comes from electricity. Heat could easily come from solar, leaving ~20w for a fan.