UPDATE: Monday, Aug 5, 2024 · 2:46:50 AM +00:00
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Irontortoise
To clear up some of the questions that have arisen in the comments regarding this KAUST prototype device:
- Isn't it just another type of dehumidifier? By definition, of course it is -- but one that requires no external energy source (other than ambient sunlight) and is entirely passive with no moving parts at all (other than the lithium chloride adsorbent recycled via diffusion and/or convection) or need for outside intervention to maintain a fairly continuous flow of fresh water suitable for agricultural purposes.
- Doesn't it require high relative humidity to extract any useful water from the atmosphere? Definitely -- it needs at least 60% RH to even begin to start the extraction process, and works best where the RH >90%, so it's not something suited for most inland arid climates. But for places like the Persian Gulf, Red Sea, or other tropical/subtropical coastal areas that suffer from high humidity at least part of the year and don't have access to alternative and affordable sources of fresh water, this could be an important new technology -- but depending of course on:
- Is it scalable and economically competitive with other alternatives like large-scale desalination of sea water? That is the real question that has yet to be answered. The scientists and engineers have succeeded in building a proof-of-concept model that works, but since it's only capable of producing 3-4 liters of water per day per square meter of surface area, it would require a pretty substantial build out and capital investment to generate a significant amount of fresh water -- even if the actual components and fabrication process are relatively inexpensive. The bottom line is just how much this new water would end up costing per liter over whatever the lifetime of such a project proves to be (1 year, 5 years, 20+ years?), and those are the sort of estimates we would need to evaluate any economic advantages it might or might not have to offer.
Found this from Tech Xplore a few days ago that could have truly revolutionary implications for helping to solve the growing fresh water shortage in much of the world.
It's estimated that Earth's atmosphere currently holds about 13 trillion tons of water in the form of water vapor, which is about 6 times the total amount of fresh water in all the planet's rivers and streams; and with each degree Celsius increase due to global warming, that capacity increases by about 7%:
Now engineers and scientists from Saudi Arabia and China have created a system that uses solar energy to extract as much as 3 liters (0.8 gallons) of water per square meter per day from air, in a purely passive way, requiring no maintenance or human operators. The study is published in the journal Nature Communications.
The system was tested by using its collected water to successfully grow cabbage during two seasons in Thuwal, Saudi Arabia.
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Existing solar-driven atmospheric water extraction (SAWE) systems typically rely on absorbing water vapor from the air. When the absorbing material reaches saturation, the system is sealed and exposed to sunlight, which begins the release of the captured water. They are an improvement over passive atmospheric water technologies such as fog and dew collection, and more available in other geographies and sites with climate constraints.
But such SAWE systems allow only one absorption-release cycle per day, capturing moisture at night and desorbing in during the day, with the slow absorption phase limiting how much water can be extracted.
Their widespread adoption is also limited by costly absorbing nanomaterials, challenges scaling up prototypes, while switching cycles requires either an active system which is prone to breakdown or a labor-intensive operation with moving parts, making the systems complex and energy intensive.
The Saudi-Chinese prototype is already 4 times as efficient at extracting water from air as the most recent (2021) MIT design, and 27 times as efficient as MIT's initial (2017) model.
