Floating Solar Device Boils Water Without Mirrors (arstechnica.com) 80
An anonymous reader quotes a report from Ars Technica: Researchers from MIT and the Masdar Institute of Science and Technology, led by George Ni, describe a prototype design that boils water under ambient sunlight. Central to their floating solar device is a "selective absorber" -- a material that both absorbs the solar portion of the electromagnetic spectrum well and emits little back as infrared heat energy. For this, the researchers turn to a blue-black commercial coating commonly used in solar photovoltaic panels. The rest of the puzzle involves further minimizing heat loss from that absorber, either through convection of the air above it or conduction of heat into the water below the floating prototype. The construction of the device is surprisingly simple. At the bottom, there is a thick, 10-centimeter-diameter puck of polystyrene foam. That insulates the heating action from the water and makes the whole thing float. A cotton wick occupies a hole drilled through the foam, which is splayed and pinned down by a square of thin fabric on the top side. This ensures that the collected solar heat is being focused into a minute volume of water. The selective absorber coats a disc of copper that sits on top of the fabric. Slots cut in the copper allow water vapor from the wick to pass through. And the crowning piece of this technological achievement? Bubble wrap. It insulates the top side of the absorber, with slots cut through the plastic to let the water vapor out. Tests in the lab and on the MIT roof showed that, under ambient sunlight, the absorber warmed up to 100 degrees Celsius in about five minutes and started making steam. That's a first. The study has been published in two separate Nature articles: "Steam by thermal concentration" and "Steam generation under one sun enabled by a floating structure with thermal concentration."
Useful for desalination plants? (Score:5, Insightful)
Re:Useful for desalination plants? (Score:4, Insightful)
It could, you probably don't want to. Overall efficiency will be moderately low - you don't for a desalination plant want stuff floating on the water for long periods, it's too hard to anchor and make reliable.
It's probably several times more efficient to have the plant on land, with 'conventional' solar collectors.
Vacuum solar panels are surprisingly cheap now.
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How is efficiency defined?
Power generated divided by man-hours. The less human effort needed, the more efficient..
With mods (Score:1)
Biggest problem would be contamination, wicks do not remove salt or sea contamination, they wick that too. So salt would be deposited on the paint layer stopping it working.
But suppose you have a clear hard layer ontop of the paint. Something that could be scraped clean easily. Then you could scrape the salt away.
Imagine a steam powered blade, turning around slowly (geared down), scraping off the salt and pushing it off the edge. I think even a small low tech mechanical approach could fix that problem.
Re: With mods (Score:1)
I saw a solar powered garbage collector for canals and harbors. It was simply a conveyor belt that went underwater, a waterwheel (for cloudy days) and solar panels. The energy was enough to drive the conveyor belt slowly (15cm/hour). Then everything from plastic bottles to tree branches was scooped up and collected in a recycling skip.
Why is this important or interesting? (Score:2)
I'm having some trouble understanding why using a commercial product, BluTec copper, in a manner in which it is intend to be used (heating water via unconcentrated sun) is news? When you build a colar water heater normally you are working to not have it boil the water. It's more efficient not to. In fact the article even says they get better efficiencies when they-- get this-- run it below 100c. Wow! alert the media and publish it in nature.
So what they did was create a thermally insullated restricte
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Because they want to boil water and make steam, not just heat water. As you point out, anybody can heat water and that's not news. They built something that makes steam which is useful in many ways...
From TFA:
"Steam that is cheaply and simply produced could become a popular way to generate electricity. It could also be used to heat buildings, for industrial applications, or even to boil seawater or wastewater to distill pure, clean water—just as the hydrologic cycle generates rainwater."
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SCRAPE the salt away? Nonsense, just rinse the device regularly with sea water.
could != would (Score:1)
There has been enough technology to end world hunger and thirst for well over a century, but it is not being utilized to do so. It is not profitable and nobody who "matters" really cares about it.
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Happenstance of where you were born in a technologically uneven world really has nothing to do with your fitness as an individual.
god-botherer? (Score:1)
Rather hypocritical of you, seeing how you are spreading the gospel of darwinism you were indoctrinated into absent any understanding, and sprinkled with racism. His comment had nothing to do with souls or religion, his point was nobody gets to chose, and you wouldn't be barking that cr@p had you been born in the "wrong place", cuz you'd be jerky drying under the sun regardless of how "fit" you consider yourself to be.
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Rather hypocritical of you, seeing how you are spreading the gospel of darwinism you were indoctrinated into absent any understanding, and sprinkled with racism.
I hate to spring to the defence of an AC against another AC, but you seem to be unaware that darwinism also implies an end to racism and even speciesism, because there are no dividing lines.
You need binary thinking to get hate crime, and modern biology is delightfully free of that..
His comment had nothing to do with souls or religion, his point was nobody gets to chose, and you wouldn't be barking that cr@p had you been born in the "wrong place", cuz you'd be jerky drying under the sun regardless of how "fit" you consider yourself to be.
"Being born in the wrong place" is a double absurdity - both because you can no more be the offspring of someone else than you could be the offspring of a wrench and a comet, and also because the human being isn't a binary on/off
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Yes, and there has been plenty of FOOD for over a century. Since 1900, "famines" have been entirely politically generated. In Somalia, when the US and Europe sent food, the food would rot on the docks because the warlords were using all the trucks. When the USA and France sent the Army into Somalia, the warlords stole the food AND the trucks.
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The total steam production will be limited to the same amount of evaporation you would get from the pond naturally.
No, and that dissimilarity is the whole point of the exercise. The pond is a huge body of water. As long as you heat that evenly (or at least a layer of non-negligible thickness, which the sun normally does, then the temperature and evaporation are low. This floating device is designed to heat up a small amount of water to a much higher temperature. This increases the overall evaporation, because energy is not used to warm up the rest of the water. Unless you want to evaporate the entire pond, there is a difference between heating up only the water you want to turn into steam and heating up all the water.
Another way to say this is: You use the energy you get to heat the part that's important (the layer exposed to the air that CAN evaporate) more efficiently.
How these things could be used isn't real obvious. Maybe along the coast to increase evaporation and moisture carried in wind that travels inland? I have seen a few diagrams of greenhouses with dew collectors on the ocean side to catch evaporated seawater for use.
Though, I can't see how they would be much better than getting the sand on shore wet, m
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>How these things could be used isn't real obvious.
Distillation. It's the hooch puck.
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Can we do cognac? I like that.
As I live and breath (Score:1)
A reasonable first post, and four good responses in a row.
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I think it's best suited for instant noodle soup. The noodles are in a plastic cup as usual. You add water. Then you remove the protective foil from the cover, put it on the cup and place it into the sun. You wait five minutes, remove the cover (danger! beware of sunburns!) and voila... instant Ramen!!! Yummy!
Thinking about it, maybe it could also be used for instant fried bacon!!!
Re:Useful for desalination plants? (Score:5, Insightful)
I should think not -- at least not in the way you're probably thinking.
The device consists of a wicking layer topped by a light-absorbing layer. This boils water, which produces more or less pure steam. It also leaves the minerals from the water in the wicking layer. If you take distilled water directly away from the device and replace it with fresh seawater, those minerals will build up until the layer is no longer absorbent. On the other hand if all you want is the heat, you run the steam-distilled water through a heat exchanger and return it to the wicking layer, reconstituting the original water.
So it'd probably wouldn't work to use this directly as a steam distiller. However you could use the heat you collect to run a separate steam distiller. That would be very inefficient, but the thing about "renewables" is that conversion efficiency is less important than low installation and operation cost, because you're not paying for your feedstock of energy; any sunshine you don't use would have been wasted anyway. So while it seems physically possible to use this device to power a desalinization plant, whether it makes economic sense depends on whether this is actually the cheapest way to run a plant.
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"sunshine you don't use would have been wasted anyway"
Is that so? Suppose we cover miles of oceans and lakes with these devices. Would there be no change in the ecology? No change in water or air temperature?
We dam rivers wherever possible, plant solar collectors over large areas, tap geothermal energy potential, and erect windmills wherever we can expect a breeze. There has been an effort to tap the energy of the surf and other wave action. The dams certainly have an impact on the environment and the other
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Well, to answer your question, of course if we covered the entire ocean, or significant fractions of it, sure there'd be undesirable ecological effects. Just like anything else that is scaled up endlessly without allowance for what economists call "externalities".
If you could internalize all externalities then the market would provide a perfect solution without any kind of regulation whatsoever. But since nobody knows how to do that, then I imagine that you'll get two regimes: (1) do whatever you want as
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Wind --> Trees
They've been messing with wind patterns for the past 100M years at-least. We've clear-cut so many that I think windmills just barely are restoring back the blockages trees have been offering since the dawn of our species.
Wasted Heat:
Either way, it's part of Earth's heat. If we could turn tons of "waste heat" into energy, we would then use the energy which creates . . . heat. We could store mountains full of batteries and it would make littl
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One early application could be emergency desalination for boaters lost at sea.
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If, on the other hand, you are too cheap or too lazy to get the gear, get the training, apply the traini
Re:Useful for desalination plants? (Score:4, Informative)
Oh, look, you've re-invented the "solar still", a WWII-era survival device that pilots would carry in their escape kits with the 1-man life raft. Inflate the balloon, add sea water, and drink distilled fresh water a few hours later. Dump the brine, add more sea water, and repeat. A few pilots survived for weeks in their rafts, eating sun-dried fish and drinking distilled water from their solar still balloons.
Huh? (Score:2)
"a material that both absorbs the solar portion of the electromagnetic spectrum well and emits little back as infrared heat energy"
The "solar portion of the electromagnetic spectrum" ? Is that trying to say "visible light" ?
And "...emits little back as infrared heat energy ..." ? (This part brought to you by the Department of Redundancy Department?)
Isn't the point of the device to emit more infrared?
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"a material that both absorbs the solar portion of the electromagnetic spectrum well and emits little back as infrared heat energy"
The "solar portion of the electromagnetic spectrum" ? Is that trying to say "visible light" ?
I think that is a bit more wider than visible light. But I agree it's not very clear how it works. Does it emit infrared becouse is hot, or for other reasons, like fluorescence? How much would it improve over normal black paint?
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Yes, absorbing light from ultraviolet and infrared part of the spectrum too. That is visible light for some species, and humans with the right hardware.
But how can something be hot and not emit infrared, a.k.a. heat, and somehow make steam from this heat/infrared that it's not emitting?
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But how can something be hot and not emit infrared, a.k.a. heat, and somehow make steam from this heat/infrared that it's not emitting?
Insulation.
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The surface is non-emitting in long wavelength infrared. This is likely due to a particular coating. You can obtain paints or do procedures like torching stainless to produce a low emissivity surface. This is common practice for solar heat collectors. Really the only thing special about this device is the controlled introduction of water so the heat delivery of the device is not overwhelmed by the volume of water.
Making steam seems quite plausible if you feel a shiny aluminum surface in the sun. The
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The coating reduces IR emission, keeps the heat in until it's hot enough to make steam.
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Of course, the sun emits more than visible light. If you want maximum heating, you'll be taking advantage of at least the infra-red portion as well, possibly more - for more details, spend a couple of seconds on Google researching, it's well documented.
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Solar energy consists of visible light plus UV plus IR
Once you absorb solar energy, you want to keep the heat from being emitted... hence, this coating which has low IR emission.
The point is to hold IR, not emit IR.
magnifying lens (Score:1)
A magnifying lens under sunlight can burn things, no mirrors required.
Steam generation under one sun (Score:2)
Why is the number of suns relevant? I don't often visit places with two.
Re:Steam generation under one sun (Score:5, Informative)
Sounds complicated (Score:2, Funny)
There's a much easier way to get steam. Details are available here [steampowered.com].
Floats, makes steam... (Score:2)
Solar hovercraft?
Sounds like essential equipment for lifeboats (Score:2)
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If your liferaft didn't come with one, you could always buy one on amazon [amazon.com]
Steven Callahan, adrift for 76 days in a liftraft, had three solar stills he used to make drinking water. He had to modify them to get them to actual be useful in the ocean.
My First World Response.... (Score:2)
Where can I get something like this to heat my pool water?
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Your standard black rubber type pool heater is basically this same thing, except it already works at scale.
Where Theory Meets Reality (Score:2)
Theoreticians never seem to work with, nor allow for, the real world of Friction and Filth (Oh! Great cover band name; I claim copyright).
System efficeincy? (Score:2)
So this thing produces 'steam'. Or more accurately it speeds up the evaporation of water above the base case of a pond sitting out in the sunlight. But how much more evaporation does it produce? And assuming we want to do something other than dry up puddles, what about the rest of the system? To utilize this steam for generation, you need to do a lot more than produce water vapor at 100 C.
I'd like to see some numbers that relate the energy captured per unit time to the insolation rate. The Arstechnica arti
Old hat? (Score:4)
Solar thermal collectors that can boil water have existed for decades. You don't need concentration for that, simply use a black absorber plate with pipes under a glass plate and put a vacuum between the absorber and the glass. Selective absorbers or glasses will improve the efficiency.
There are two problems with it: The generated steam will have a low temperature not much above boiling water. Most industrial applications need process steam of a much higher temperature (although there are some exceptions).
There are also problems with the two-phase flow of the steam-water mixture in the pipes, which is generally unstable and difficult to control. Technically it is much easier to concentrate sunlight, use an oil with a high boiling point as the carrier liquid and use it to generate the steam in a seperate unit.
Two years in the making (Score:1)
Noted two years ago at another web site [tikalon.com].