Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Simple, solar-powered water desalination (2020)

news.mit.edu

Post reply on HN
Print view View original

101–110 of 241 posts

Re: Simple, solar-powered water desalination (2020)

#101

Post by trainsplanes »

ComodoHacker wrote: post #98
crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

It's an example of a good old scientifically flavored clickbait. The energy efficiency of anything cannot exceed 100% (until I missed something groundbreaking in physics).

It very much can exceed 100% and it’s not a measure invented for click bait purposes.

Look up heat pumps. You can make things hotter by moving heat than you could by directly heating it by burning fuel.

Re: Simple, solar-powered water desalination (2020)

#102

Post by MrsPeaches »

trainsplanes wrote: post #101
ComodoHacker wrote: post #98

Earlier quoted context omitted.

It's an example of a good old scientifically flavored clickbait. The energy efficiency of anything cannot exceed 100% (until I missed something groundbreaking in physics).

It very much can exceed 100% and it’s not a measure invented for click bait purposes. Look up heat pumps. You can make things hotter by moving heat than you could by directly heating it by burning fuel.

As another comment pointed out, it’s usually called the Coefficient of Performance in this case.

Which is to say this is click bait, because saying it has a COP of 3.85 isn’t anywhere near as sexy, whilst being technically more accurate.

Re: Simple, solar-powered water desalination (2020)

#103

Post by isthisnametaken »

einpoklum wrote: post #80

> The system delivered pure water That's toxic! We can't drink pure water. You have to maintain _some_ of the minerals in there, you just want to take most of the NaCL out. Does the system avoid this over-distillation? i.e. is the water properly potable, or is it just not-salty?

Sorry, what? Pure water isn't toxic. And you can get minerals from other sources.

That's like saying tap water is toxic because it doesn't contain a balanced diet of vitamins.

Re: Simple, solar-powered water desalination (2020)

#104

Post by londons_explore »

jeroenhd wrote: post #67
femto wrote: post #48

Earlier quoted context omitted.

A comparison with reverse osmosis: 2.46kWh/m^3 (energy consumed per unit of water produced) is claimed for reverse osmisis [1]. This equates to 8.86MJ/m^3. Output for this still is 7L/(m^2.h) Assume a solar flux of 1kW/m^2. Energy consumed per unit of water is 1kW/m^2 / [7L/(m^2.h)] = 3.6MJ/0.007m^3 = 514MJ/m^3. Assuming the above is correct (check anyone?), the still uses 58 times more energy than reverse osmosis. T…

> In production, they think a system built to serve the needs of a family might be built for around $100. I think this is much more important to a great many people than the theoretical efficiency of reverse osmosis. Percentages greater than 100% always do well in media reports about these topics, but they're not necessarily the point of the exercise. If the goal was to produce a system that's as efficient as possibl…

Nothing about reverse osmosis can't be scaled down in size or cost.

The actual membranes are $9 for enough for 100 gallons per day (retail prices, [1]).

High pressure pumps and hoses scale linearly. Solar panels scale linearly. Filters scale linearly.

In fact, using this solar fountain [2] as the basis for the design, and switching the pump impeller for a high pressure version, and the nozzle for an RO membrane and hose, you immediately have a drinking water machine for a few people for $20. The fountain already has a pre-filter built in.

[1]: https://www.aliexpress.com/item/32669709750.html [2]: https://www.aliexpress.com/item/1005002883892948.html

Re: Simple, solar-powered water desalination (2020)

#106

Post by pjerem »

Cthulhu_ wrote: post #97
FartyMcFarter wrote: post #71

Earlier quoted context omitted.

The sea is a big place. I could imagine perhaps some very localised effects near the plant, but even this isn't obvious.

> imagine > perhaps > but even this isn't obvious So basically you're admitting you don't know anything about the subject, but you're making a conclusion anyway. It's OK to admit you don't know enough about a subject, and it's OK to not comment or theorize based on no knowledge besides an imagination.

I didn’t know that making assumptions while clearly saying you are making assumptions is forbidden on HN.

Re: Simple, solar-powered water desalination (2020)

#107

Post by squarefoot »

FTA: "Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers."

The capabilities are freaking interesting, but let's say someone builds a big enough settlement on a coastline or island in which every building has one or more of these devices on its rooftop. Would this release back enough salt so that the surrounding seawater becomes hostile to its previous lifeforms? Also, since then the water used in the process would contain more salt, how much would that render the device less efficient?

Re: Simple, solar-powered water desalination (2020)

#108

Post by SiempreViernes »

londons_explore wrote: post #104
jeroenhd wrote: post #67

Earlier quoted context omitted.

> In production, they think a system built to serve the needs of a family might be built for around $100. I think this is much more important to a great many people than the theoretical efficiency of reverse osmosis. Percentages greater than 100% always do well in media reports about these topics, but they're not necessarily the point of the exercise. If the goal was to produce a system that's as efficient as possibl…

Nothing about reverse osmosis can't be scaled down in size or cost. The actual membranes are $9 for enough for 100 gallons per day (retail prices, [1]). High pressure pumps and hoses scale linearly. Solar panels scale linearly. Filters scale linearly. In fact, using this solar fountain [2] as the basis for the design, and switching the pump impeller for a high pressure version, and the nozzle for an RO membrane and h…

Ah, so what you are saying is that this is already deployed on a large scale to solve distributed water issues?

Re: Simple, solar-powered water desalination (2020)

#110

Post by MauranKilom »

ghshephard wrote: post #87
eterevsky wrote: post #12

> 1.5 gallons of fresh drinking water per hour for every square meter 7 litres per m^2 per hour.

Back of the envelope - say that you could get 7-8 hours of sunlight a day that could destill water. That would mean ~50 liters/day. ~20 Days to get 1m^3. Reverse Osmosis costs approx $0.50/m^3 water, so your payback on a $100 system would be ~200 * 20 Days or 4,000 Days to equal what you could get for spending $100 on buying water from a reverse osmosis system. The objective here isn't large scale economics, but self…

Looking at a 10+ year time frame, I feel that maintenance cost would become the dominating factor. For both.
Post reply on HN