This device was discussed earlier on HN and that article goes a little further into the design decisions for the device. (1) The focus is not efficiency or volume. It's compact, portable, robust, maintenance free. No filters, no high pressure components, suitcase size, able to use brackish water. They are not trying to solve industrial scale efficient desalination. They are trying to solve small scale portable desalination. You are measuring them against metrics they're not trying to achieve and it's no surprising they fail at this test.

(1) https://news.ycombinator.com/item?id=31200793, also linked in the article for this post.

Not to mention that the perspective siliconescapee boils down to "You could buy X off amazon today" which is not even possible for loads of people, as Amazon doesn't operate in many countries, and there are plenty of countries where Amazon doesn't even ship to. Then we have the 10% of people who live in poverty and wouldn't be able to afford ordering it anyways. Those are the groups that would be most helped by a device with these characteristics as well (easy maintenance and low ongoing cost).

At least 1.3 billion people live in poverty, much more than 10%.

That depends on your definition of poverty; 10% of the world is in “extreme poverty” of $1.00/day in 1996 prices ($2.29 in 2021),

But this device has the exact same problem you're describing, is less efficient, costs more and requires power. Novelty is the only upside

The only device I could find on Amazon that fits the description of an inflatable desalination device is https://www.amazon.com/Aquamate-Solar-Emergency-Purification... and it reportedly produces between 0.5 and 2 liters of water per day. That’s great if you have none, but the device being discussed here produces substantially more. So it’s not just a novelty thing.

Efficiency is less important in scenarios like tropical storms, drought, and infrastructure crises, or places where common western infrastructure is non-existent. Costs are also less important as they are cheaper over time as the costs of maintenance becomes lower. Places lacking infrastructure are also helped by outside organizations who donate knowledge and equipment. Considering that this device can be solar-powered (and these bespoke areas where infrastructure is non-existing generally are _very_ sunny), requiring power seems like a lesser problem.

But what are the use cases for a device that filters 0.3L of water an hour using 20W - that's still a fair amount of electricity?

There are many ways to use the sun to desalinate that seem more appropriate to getting drinking water to humans in poor parts of the world.

For example, this is another MIT project: https://news.mit.edu/2022/solar-desalination-system-inexpens...

According to them, their prototype does use 20Wh per liter and produces 0.3 liters per hour. It’s not 20Wh per 0.3 liters. That’s USB charger level of electricity, my 100 EUR foldable solar charger produces more on a good day.

The interesting part about this is probably that even the prototype is fairly compact and weighs like 10kg and that they claim to be able to achieve that with brackish water. If they can prove that it’s as robust as claimed, that sounds like an interesting technology.

Uhh just letting you know a device that uses solar energy is not maintaince free and saying that it is would be naive at best and misinformative at worst. It's an even bigger problem in countries where accessibility for such parts does not exist or the expertise to maintain such equipment. In reality a project like this is rather useless and after a few years of use if it ever received any it would belong in the trash.

But that's what most hackathons are in reality anyways.

The device needs power, but solar is not a requirement. But you’re correct, nothing is ever absolutely maintenance free, especially if it contains moving parts.

However, their envisioned use case is not “helicopterdump across the desert” but very specific use cases, often for people with technical skills:

> This could enable the unit to be deployed in remote and severely resource-limited areas, such as communities on small islands or aboard seafaring cargo ships. It could also be used to aid refugees fleeing natural disasters or by soldiers carrying out long-term military operations.

Whether they succeed in making a device useful these cases is a good question, but I consider it pretty dismissive that you characterize a 10 year research effort as “most hackathons”

I see the majority of these grant styled competitions as just this, hackathons. Besides the prestige involved the majority of these inventions often prove to have little to no value to often not even doing as advertised. The way we incentive academic funding and research is backwards and often more than not broken at its fundamental core. It's compelled further due to these research rings broken into their own hierarchical technocratic groups.

Without knowing more about this device it's a bit hard to make a true comparison to existing marine RO devices but there are a few reasons I've been following with (skeptical) interest:

- Low volume - RO devices don't scale down well. The Katadyn 40E is the smallest watermaker I can find and it produces 6l/h. This is an insane amount of water that I have no use for. 10l a day would be enough for two people. Unfortunately there aren't cheaper and lighter options available.

- Storage - No pickling would be really nice.

- Membrane - Not needing to replace membranes would also be nice.

- Efficiency - I don't care too much about efficiency because most of the time during the day we have plenty of power from 400W of solar panels sized for days and days of cloud. That said, smaller RO devices also have poorer efficiency, e.g. 9Wh/l in the 40E. Other results in the literature suggests there could be plenty of room left to improve in efficiency from the MIT prototype.

Depending on cost, I think there's a niche for something that addresses the lower end of the market in watermakers.

As someone who uses a kitchen more than a galley (i.e. I'm a land crab), I had to look up if "pickling" had a special meaning here.

It turns out to be kinda true, nobody is putting components of their watermaking system [1] in acidic solution for preservation and flavor, but they are putting them in sodium metabisulphite solution and that chemical seems to be useful for disinfecting and so on [2].

[1]: https://www.openoceanwatermakers.co.nz/pickling-your-system....

[2]: https://en.wikipedia.org/wiki/Sodium_metabisulfite

If you can lower the transmembrane pressure you will get less output for less power and no fouling of the membrane. The economics of consumer choice drive design towards higher outputs and fouling.

Not using filters is huge! RO watermakers are really sensitive to poor quality water. Algae from last year's heat wave knocked out a lot of watermakers in Pacific waters.

From the paper

> The portable system desalinates brackish water and seawater (2.5−45 g/L) into drinkable water (defined by WHO guideline), with the energy consumptions of 0.4−4 (brackish water) and 15.6−26.6 W h/L (seawater), respectively.

So it consumes 26Wh/L turning nasty lowtide into drinkable water with no filter.

A 300W solar panel could then produce 10L of water per hour for probably 5 hours a day. 50L a day per panel. That is amazing!

I don't know why some people are so obsessed with efficiency. Efficiency is, at best, one attribute of many which make something practical. We have had engines that are 50% thermally efficient for decades now, but no automaker has attempted to produce them because they are impractical in hundreds of other ways.

Not only would I buy this for my boat, but I would replace my more efficient spectra watermaker with it. Less noise and less maintenance are massive advantages.

Right. Panels are so cheap now that, unless you are limited in how many panels you can physically install, lower efficiency just means another panel. Even then, maybe you cant a pair of them in place of one so one picks up morning light, and the other afternoon.

Yea.

- "This energy storage is only 30% efficient".

- "Yes but it's dirt cheap and so is solar peak power."

> watermaker that uses 4w/liter

I think you have a typo there, but I am not sure what you mean. Maybe 4Wh/liter? (Knowing nothing about desalination, that sounds low, though)

Yes, this device (first I found from google) produces 100L/hour using 400 Watts

https://www.nauticexpo.com/prod/schenker/product-23417-55567...

Seems about right, the Katadyn PowerSurvivor 40E/12 V mentioned in another comment is 12 V, 4 A and 5.7 l/h, i.e. 8.4 Wh/l.

I wonder how much energy it takes to make the RO membranes.

I'd imagine that most beachfront properties have basically unlimited water, but are instead throttled by electricity costs.

Output water vs input water efficiency (20% in this case? 1-liter output from 5-liters input saltwater) matters in some cases, but not others. Since we all live in different terrains and locations, some inventions will be useful in some areas, while other inventions are useful in others.

You can imagine that, but a solar panel is cheap if it delivers 50L/day.

If it doesn't use filter mediums, where does the salt and contaminants go?

Even devices that use Reverse Osmosis usually don't aim to catch all contaminants in the filter - they use a membrane/filter to separate the clean water output from a waste water stream that contains the contaminants/salts in higher concentration. This device effectively tries to replace the filter/membrane with an electrical current:

From https://news.mit.edu/2022/portable-desalination-drinking-wat...:

> their unit relies on a technique called ion concentration polarization (ICP), which was pioneered by Han’s group more than 10 years ago. Rather than filtering water, the ICP process applies an electrical field to membranes placed above and below a channel of water. The membranes repel positively or negatively charged particles — including salt molecules, bacteria, and viruses — as they flow past. The charged particles are funneled into a second stream of water that is eventually discharged.

Down the drain.