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Earth Technology

Scientists Develop "Paint" To Help Cool the Planet 145

AaronW writes Engineers at Stanford University have developed an ultrathin, multilayered, nanophotonic material that not only reflects heat away from buildings but also directs internal heat away using a system called "photonic radiative cooling." The coating is capable of reflecting away 97% of incoming sunlight and when combined with the photonic radiative cooling system it becomes cooler than the surrounding air by around 9F (5C). The material is designed to radiate heat into space at a precise frequency that allows it to pass through the atmosphere without warming it.
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Scientists Develop "Paint" To Help Cool the Planet

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  • What about for cars? (Score:2, Interesting)

    by Anonymous Coward

    Cars being greenhouse ovens is a terrible issue. Not just because it's uncomfortable getting into the car on a hot day, but because people accidentally kill pets and children by leaving them in a hot car every year (and others not so accidentally). Surely there's better tech than what we use today to prevent our automobiles from becoming lethal ovens.

    • Oven Tech (Score:5, Funny)

      by Anonymous Coward on Thursday November 27, 2014 @08:18PM (#48476555)

      Surely there's better tech than what we use today to prevent our automobiles from becoming lethal ovens.

      Certainly there is. You can just cook your kids and pets at home, no need to waste the gas going out at all. Home ovens have been large enough to do this for decades now. People are so wasteful!

      --Hannibal

      • by Anonymous Coward on Thursday November 27, 2014 @08:28PM (#48476605)

        Vegetarian Stew

        Serves 20

        Peel, core, and slice one vegetarian.
        Place in trunk of black car for two days.
        Season to taste.

      • Surely there's better tech than what we use today to prevent our automobiles from becoming lethal ovens.

        Certainly there is. You can just cook your kids and pets at home, no need to waste the gas going out at all. Home ovens have been large enough to do this for decades now. People are so wasteful!

        --Hannibal

        Now, see!?

        That is the kind of straightforward and direct, logical, practical, problem-solving engineer-style thinking /. *used* to be known for right there, something that seems to have almost disappeared from /.!

        Bravo Sir, bravo!

        Strat

    • For cars - no show stoppers. But you can have it in any colour you want as long as it's Brilliant White.

      Srsly. Any other colour (OK, I'll exclude pastel whites ; say anything with an albedo of less than 90% or so) would absorb more light/ heat than this tailored IR radiator can emit to space.

  • Yes... (Score:5, Insightful)

    by pushing-robot ( 1037830 ) on Thursday November 27, 2014 @08:22PM (#48476581)

    Scientists Develop "Paint" To Help Cool the Planet

    They're calling it "White".

    Seriously, though, it's a mirrored silver paint with some nanoparticles mixed in to make it even cooler (pun intended). But if people aren't painting their roofs white and silver today, do they really think their paint will change that?

    On the other hand, a radiator that reflects sunlight sounds promising for other applications, like heatsinks for space probes.

    • Re:Yes... (Score:5, Insightful)

      by rtb61 ( 674572 ) on Thursday November 27, 2014 @08:37PM (#48476641) Homepage

      Would people paint their roofs to save money, you bet they will but how cheap is the paint, how clean does the roof need to be, how cheap is it to apply and how long will it last. I would have no qualms about painting my roof white, as long as I can get it done cost effectively enough. Of course one other thing, how well does it perform after it is no longer pristine, how self cleaning is it with rainfall or do I have to get up there and clean it every once a month to maintain performance. When it comes to using white as default for roofs, it is easy enough for many countries to legislate that for all new structures that is mandatory and provide subsidise for existing structures.

      • And can I take it off in the winter while the sun is (slightly) offsetting my CO2 emissions from heating house?
      • by Lumpy ( 12016 )

        White steel roofs last 20 years without problems. Dont use this junk paint, get a standard white powdercoated steel roof and call it done. Plus you end up with a roof that will last over 2 decades and eliminate leaks, Ice buildup, etc....

        • Is it ok if I keep my slate roof instead which has lasted about 100 years?

          • by Lumpy ( 12016 )

            Only if it's white. Problem is American homes are not built strong enough and will crush instantly under the weight of a Slate roof.

            We build complete crap here in the USA.

      • I assume the governments would then assume liability for all the car accidents caused by drivers blinded by the glare. There are many reasons white roofs haven't really caught on, and a simple efficiency boost won't fix things.

        If you're looking to paint your roof, I'd recommend modern coatings which are IR-reflective but absorb visible light. Some reflect UV as well.

        • White roofs are very common where I live in sunny Brisbane Australia. My own is white with the beautiful name of "Sea Spray". Though lots of people opt for dark coloured tiles, it seems to be the norm for tin roofs to be light.

      • Why paint? Presumably we're talking about houses here (unless we own apartment complexes). Instead of white paint, buy light colored shingles or ceramics.

        I would imagine the first couple on the block will be eye sores, but as more people get into it, they'll look more in place.

        • by rtb61 ( 674572 )

          Cost efficiency is the driver, by the way cost efficiency does not mean cheap it means how much performance you get for your investment, where sometimes paying more is more cost efficient. Why paint, because replacing say roof tiles is very expensive. Not that this is new, a 30+ year old industrial sub-division created by the South Australian government had already mandated all buildings have white roofs, so nothing new (for the crazies, no it did not cause planes or cars to crash, especially considering t

    • by Lumpy ( 12016 )

      and you nailed it. This "paint" is raging BS. simple latex white paint is exactly as effective as this paint is. so buy a $6.95 gallon of bright white latex and ignore this snake oil.

      • You're missing the point - if you read the article the reflectivity is actually a bonus feature, the primary feature is that it radiates heat at a frequency to which the atmosphere is transparent, meaning that you can potentially use radiative cooling during the day in normal conditions almost effectively as you can at night in the desert (or in space). And if you've ever been in a non-tropical desert at night you know it can get cold *fast* once the sun goes down, even in the summer.

      • by AmiMoJo ( 196126 ) *

        If you bothered to read TFS you would see that they are claiming that, unlike normal white paint, their coating reflects the heat in a way that prevents it heating the atmosphere so much. So they are saying that removes more heat from the planet than normal white paint does.

        They are not claiming it is significantly better than white paint at cooling your house, they are claiming it is significantly better at cooling the planet and reducing air temperature in urban areas.

        • by Anonymous Coward

          and if you understood simple math you would know that if every building on Earth were painted with this stuff it would have a negligible effect on the temperature because the area isn't that great.

        • by Lumpy ( 12016 )

          If you bothered to read the article, you would see they talk about using Titanium Dioxide. the WHITE COMPONENT IN WHITE PAINT.

      • and you nailed it. This "paint" is raging BS. simple latex white paint is exactly as effective as this paint is. so buy a $6.95 gallon of bright white latex and ignore this snake oil.

        Outside the scope of "does the article's material do what it says", this comment is still potentially false. Around half of the sun's energy that reaches the surface of the earth is not in the visible spectrum. "Bright white latex" paint is designed to be highly reflective in the visible spectrum, but makes no guarantees outside of that. You are much better off purchasing paint specifically designed to be highly reflective across a much broader spectrum.

    • a radiator that reflects sunlight sounds promising for other applications, like heatsinks for space probes.

      Sounds more like an oxymoron: radiation and reflection are two related but different processes. A perfect radiator reflects nothing, and a perfect reflector radiates nothing.

      Parts of spacecraft that need to be cold (like infrared telescopes) are cooled by radiators that are kept pointed at dark space, with reflective shrouds that keep sunlight off them.

      • I don't mind when people state clearly that they don't really understand the absorption & radiation equations, but it does kinda piss me off when these same people pontificate as though they did.

        Here's how this new microlayer thing works:

        First, it's highly reflective in the visible. That keeps a lot of energy from every entering (and being absorbed in) the building.
        Second, it's highly absorptive in the IR. Due to the reciprocity laws, this means it's also highly emissive in the IR (and btw it's also N

        • The microlayer is also highly reflective in the near infrared range as a not insignificant portion of the sun's radiation is in the near IR. It is the far IR that the material highly absorptive/emissive.
          • Thanks for the correction. I agree that the term "IR" is used for rather a wide range of wavelengths.

        • I don't mind when people state clearly that they don't really understand the absorption & radiation equations, but it does kinda piss me off when these same people pontificate as though they did.

          We definitely share that hot button. Good analysis.

    • by mysidia ( 191772 )

      If people aren't painting their roofs white and silver today, do they really think their paint will change that?

      I would if the Home owner's association police would allow it.

    • The actual article is a bit shallow on detail, but here's my interpolation...

      Infra-red is quite a broad bit of the spectrum. It starts at about 800nm as light we can't quite see, and security cameras use this band with an infra-red illuminant. If we go down to about 2000nm, we are into the mid-band where some IR cameras operate. These can see hot objects but cannot people by their radiated body heat. There is a gap at about 3500nm where water vapour absorbs and emits, and cameras do not work well. Then t

    • White in the visible and black in the infra red. Not exactly a new idea but based on the strange words they are using I suspect that they are trying to patent this.
    • In a vacuum you use this to control the temperature of a spacecraft http://en.wikipedia.org/wiki/M... [wikipedia.org]
  • by jphamlore ( 1996436 ) <jphamlore@yahoo.com> on Thursday November 27, 2014 @08:23PM (#48476583)
    According to Wikipedia's entry on hafnium [wikipedia.org], "Hafnium reserves are projected to last under 10 years if the world population increases and demand grows."
    • by Anonymous Coward

      Reserves are defined as the quantity of metal that has been proven to be economically mineable. Generally speaking, if the price of an element goes up, the amount of reserves will also go up, because more more mineralized rock will become ore (ore being rock from which minerals can be extracted at a profit). Another factor that affects reserves and ore are metallurgical processes; a new process which allows for economic seprataion at lower concentrations will have the effect of increasing reserves. So, you

    • by Michael Woodhams ( 112247 ) on Thursday November 27, 2014 @08:58PM (#48476711) Journal

      The (paywalled) research paper states: "The use of HfO2 is, however, not essential, and can be replaced with titanium dioxide (TiO2), which is less expensive."

    • Probably only about 50% of it can be used effectively...

  • ... there's not enough paint to paint the Earth [xkcd.com]:

    According to the report The State of the Global Coatings Industry, the world produced 34 billion liters of paints and coatings in 2012. ...

    If we assume paint production has, in recent decades, followed the economy and grown at about 3% per year, that means the total amount of paint produced equals the current yearly production times 34.[6]\((1+\tfrac{1}{0.03})\) That comes out to a little over a trillion liters of paint. At 30 square meters per gallon, "Square meters per gallon" is a pretty obnoxious unit, but I think it's not quite as bad as acre-foot (a foot by a chain by a furlong), which is an actual unit used in technical papers I was trying to read this week. that's enough to cover 9 trillion square meters—about the area of the United States.

    So the answer is no; there's not enough paint to cover the Earth's land, and—at this rate—probably won't be enough until the year 2100.

  • by jeffb (2.718) ( 1189693 ) on Thursday November 27, 2014 @08:29PM (#48476609)

    Passively cooling an object below ambient temperature seems... counterintuitive. I think I understand what's going on here, but I'd like to see some more thorough discussion. Particularly, I'd like to know how you can find any passband in which an object at ambient temperature radiates more heat than it takes in from direct solar exposure, except the bands blocked by the atmosphere.

    • Re: (Score:2, Informative)

      by Anonymous Coward

      Direct solar exposure is reflected, then the reflected light and internal heat radiation is modulated to a frequency that passes easily through the atmosphere. I'd have to question the efficiency of modulation, which seems to be where their breakthrough occurred.

      • by Rei ( 128717 )

        This "modulation" happens all the time, few things in this universe are true blackbodies, most prefer to radiate in specific bands. They're apparently using a material that tends to radiate only on one narrow band at regular earth temperatures.

        Not sure how much benefit this provides to the building owner, to the point that they'd be willing to cover their building in hafnium-and-silver coated panels, rather than just white paint...

        • White paint only reflects light, and inhibits radiative cooling since radiation follows the same curve as absorption. This surface might actually be *less* effective than a good roof-white* paint at reflecting incoming sunlight. But if you've ever been in the desert and noticed how rapidly it cools at night you've gotten a little taste of what a dramatic effect radiating into the near absolute zero blackness of space can have. There they accomplish it by having extremely low water levels in the local atm

    • by skids ( 119237 ) on Thursday November 27, 2014 @08:58PM (#48476709) Homepage

      "Ambient" is important to define here. The temperature of the air is not actually playing much of a role in the black body equation. If the sky was made of more buildings at ambient temperature, then the story would be different, but other than the sun it's mostly an open pit into which anything radiated never returns. Also keep in mind that that figure may be referencing the temperature of the air near the whole building including the lower floors; it is cooler up high on tall buildings.

      The idea is that the heat provided from within the building and the heat from the 3% of sunlight that gets through the mirror all pools and the mirror material then converts it to a specific passband. So you have more heat pooling than what comes in on that passband.

      How effective this system remains when contaminated with a coat of dust is a question. Also comparative advantage to absorbing the heat/light and using it to power AC.

      • The dust causes a problem only when it becomes so dense as to completely obscure the paint. The dust will heat up from sunlight and also heat up from the radiation from the paint. As the dust heats it will radiate infra-red back towards the paint. As long as the paint supports some level of heat conduction 'horizontally' through the paint, those tiny areas of paint that are not obscured by dust will start to radiate more and more until heat equilibrium is again established.

        A light covering of dust tha
    • by Rei ( 128717 )

      It's not the ambient temperature of air that's key here, it's the ambient temperature of space, which is about 2,7K.

      All objects are constantly radiating energy and receiving energy back from other things that are radiating. When two objects in radiative exchange are roughly the same temperature, this balances out. But when one is hotter than the other, the hotter one loses more energy than it takes in, and vice versa. And it's not just a little difference - radiative heat loss is proportional to the absolut

    • by art6217 ( 757847 )
      Look at this in another way: there is some planet with different objects placed on its surface, and these are well--isolated from each other. It would not be surprising, that each of these objects has a different temperature, would it? Because of e.g. its colour or its radiation surface. Now, let one of these objects be the air, and the other be some well--isolated, well--radiating building. Would not it be cool to put a thermodynamic engine in that building, in order to produce energy by reversing the gr
    • Think of a ground frost. At night thermal radiation from the ground goes through the atmosphere resulting in cooling but air can only radiate weakly (it is transparent) so cools far less. The result is that the ground ends up colder than the air.
  • This painting reflects infrared instead of radiating it, but does it change anything to global warming? If there is too much CO2 in the atmosphere, the heat is trapped, does reflecting instead of radiating changes the game?

    Or is it just about making sure visible light is not turned into infrared by radiation?

    • Actually the primary greenhouse gas is water, but water only absorbs a certain frequency-band of infrared radiation. CO2 then absorbs another adjacent frequency band, and between them they cover most of the frequency band at which things at earth-normal temperatures generally radiate thermal energy, thus trapping the heat by re-radiating (it's not really reflection) a large portion of the absorbed heat back down to the surface.

      This surface though gets tricky - it has apparently been designed to radiate hea

  • It sucked. Why did they have to be on a train? That didn't make any sense at all.

  • by Michael Woodhams ( 112247 ) on Thursday November 27, 2014 @08:53PM (#48476691) Journal

    For those fortunate enough to have institutional access, the research paper is here [nature.com].

    Quickly picking some highlights:
    The atmospheric transmission window is between 8 and 13 microns. They achieved 4.9C below ambient in direct sunlight at 850 watts per square metre. Cooling power was 40.1 watts per square metre. Emissivity (equivalently absorptivity) averages about 70% in the 8-13 micron window (estimated from a plot.)

    Here's a quick back-of-the-envelope calculation
    90% reflective white paint: absorbs 85W/m^2
    97% reflective foil: absorbs 25.5W/m^2, an improvement over white paint of ~60W/m^2
    This film: emits 40W/m^2, an improvement over simple foil of ~60W/m^2.
    So in this scenario, the special film gives twice the benefit compared to just going for something simple and reflective. (The 90% for white paint is guess-work. The 97% for 'foil' is just matching the special film. Perhaps someone can update the calculations with better founded values.)

    The summary title is highly misleading.

    It is not paint, it is a manufactured film. It cools buildings, not planets. Yes, with enough you could cool the planet, but if you wanted to take that route, it would be much more cost effective to just use aluminium foil and use a marginally larger area of it (or, indeed, white paint.) Back in the real world, the way this invention cools the planet is by reducing electricity demand for air conditioning. (I saw another article about this in which one of the authors makes exactly this point.)

  • Is it so cheap that using this tech to get rid of excess solar energy is better than using that energy to produce electricity, to cook, to provide hot water or for some other use? I am much inclined to doubt that.
  • In some ways Venus is a much more attractive target for off-Earth human expansion than any of the other possibilities. Notably, it is closer to the Sun so anything solar-powered would work about twice as well. In other ways it is very unattractive indeed. One of those is surface temperature, several hundred degrees too high for most Earth life forms.
    Could this stuff, or something related, help us reduce temperatures on Venus? http://en.wikipedia.org/wiki/Terraforming_of_Venus/ [wikipedia.org]
  • the roofing materials that are used around here have been used for a long time because they do the job and also are known to me safe for capturing drinking water. What is the toxicity of this stuff? we just had our first real summer temps the other day at 42c/107.6f. I would love a cooler house but not if it is going to poison my family.
  • by Greyfox ( 87712 )
    I foresee an ice age in our future!
  • ...drop everything you’re doing RIGHT NOW and come here to Siberia. 32C today, 27 this weekend.

    • Also, Slashdot, get real and learn not to lose Unicode.

      -32 (resp. -27) degrees Centigrade.

      • by dbIII ( 701233 )
        Would have loved to be there instead of here when in was +42C over the weekend, and I'm not even in the tropics.
  • Great innovation. I hope i can see it very soon in market for customer like us.
  • There is a cheaper alternative. Coat the surface with small crystals of oxidane. Its very good at reflecting heat. In large quantities it is very good at absorbing heat..
    I have a driveway full that you can have for free, just bring your own shovel.

  • Since it is 1 degree (f) here this morning, I would like the paint / cover to warm my house. Although the snow on my roof does provide some insulation and would interfere with the collection of solar heat.
  • Underrated film [imdb.com] but I seem to recall that painting the atmosphere (or something similar) caused a global catastrophe. Obviously not saying this will result in the same unfortunate scenario but just found it interesting.
  • So what's better for the planet? Painting my roof with this stuff or covering it with solar panels?
  • The surface area to paint is insufficient to have a meaningful intended effect. 1) It won't stay clean for long reducing effectiveness. I know, as the former white roof of my business is now a spotted light gray. 2) Coating adhesion is not eternal. It's expensive to repaint often. 3) The greenhouse effect would just bounce much of the reflected infrared right back to heat up some other part of the earth. Paint to cool the planet is a nice idea, but terribly useless. Just go plant a tree somewhere and call
  • I wonder if one could paint this on a wood stove to increase the heart output.

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