Very white paint

Darunion

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In other news, water is wet, and if you drink it when your thirsty, you're not thirsty any more.

Seriously, is this what science is doing these days? Who knew white paint reflected light.....

It is about increasing the percentage of sunlight that is reflected by the paint. If you reduce the amount absorbed you reduce the amount of heat at the surface. So in applications where you don't want heat, that would be the benefit. Even mirrors you find in the house still absorb about 10-15% of the light that hits them.

For me this is just as interesting as the black paints that absorb more light. At the theoretical 100% you wouldn't even be able to perceive it as anything other than a void in space.
 

Zarathustra[H]

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I feel like it has been well established for hundreds of years that lighter colors absorb less heat from the sun than darker colors do.

This more reflective paint may be a slight improvement. That's nice I guess.

Who wouldn't want to save on their electricity bill by having a lighter colored roof?

The trick is that there are seasons. Most places in the US have seasons that require heating and seasons that require cooling. You'd have to compare the financial benefit in the warm season to the financial penalty in the cold season to see if this works well, unless you want to change colors twice a year :p
 
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travm

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It is about increasing the percentage of sunlight that is reflected by the paint. If you reduce the amount absorbed you reduce the amount of heat at the surface. So in applications where you don't want heat, that would be the benefit. Even mirrors you find in the house still absorb about 10-15% of the light that hits them.

For me this is just as interesting as the black paints that absorb more light. At the theoretical 100% you wouldn't even be able to perceive it as anything other than a void in space.
Wake me up when invisibility paint is a thing.
 

notarat

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Whenever our ship went near equatorial waters the Deck Department would paint the deck above the mess decks with white paint so the AC units didn't work as hard to keep the mess decks cool for sailors eating their meal. The deck above the Admiral's stateroom was painted silver as well.
 

Wat

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I think the main point is that this paint can reduce the temperature below ambient.
As a building covering, it would reduce cooling costs, but increase winter heating costs, so it seems kind of pointless to me in, except in the tropics.
But if a simple white painted device could condense water out of the air, dry places along the coast would have an alternative to desalination.
 

GreenLaser

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Captain Obvious would like to thank the sponsors for this breakthrough tech.... Purdue U, Krylon, Rustoleum and Dutch boy. :) ...Oh and 3M, Dow Corning must be in there somewhere too.

Like all the short sighted solutions the professional idea people churn out ...the carbon footprint of producing the chemicals and making the paint, deploying the paint and keeping the paint clean enough to work would be many times larger than doing nothing at all.
 

Jonnycat99

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Looks like Sherwin Williams is going to have to update their logo.

SWP.jpg
 

KD5ZXG

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"Ultrawhite BaSO4" too technical, just paint it "Milkshake Duck."
A legit milkshake ingredient used for XRay imaging, so go figure.
Everyone loves milkshake duck till they learn its also for enemas.
 
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gigaxtreme1

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Maaan, and I thought they came out with a new coffee creamer. At least, that's what my daddy called it.
 

SvenBent

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It is about increasing the percentage of sunlight that is reflected by the paint. If you reduce the amount absorbed you reduce the amount of heat at the surface. So in applications where you don't want heat, that would be the benefit. Even mirrors you find in the house still absorb about 10-15% of the light that hits them.

For me this is just as interesting as the black paints that absorb more light. At the theoretical 100% you wouldn't even be able to perceive it as anything other than a void in space.
The person you are quoting clearly had a need to feel suerior on a topic he didn't even understand. And now you destroyed it.... You are a bad bad person
 

Armenius

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Would make a nice contrast with the blackest paint currently in existence:

I love how that stuff just makes everything look fake to a camera.
They mention coating cars with it. It'll burn the retinas of onlookers.
This. I hope it gets made illegal to put on cars or otherwise we're going to need to be allowed to put tint on our windshields.
 

Kalessian

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One interesting use of white paint is as a diffuse reflector for the backside of a solar cell. It's a cheap way to reflect light that made it through the cell back up into the cell for another chance to be used.
 

serpretetsky

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One interesting use of white paint is as a diffuse reflector for the backside of a solar cell. It's a cheap way to reflect light that made it through the cell back up into the cell for another chance to be used.
Why not just use a metal reflector on the back side? Aluminum maybe?
 

Kalessian

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Why not just use a metal reflector on the back side? Aluminum maybe?

This topic used to be my job so I'll try not to go overboard here but they do. In the research world they're a bit ahead of industry in terms of design but I believe most crystalline solar cell panels you buy will use a textured mirror made from a two-layer stack of first conductive oxide like ITO or ZnO then with metal. In lab we use silver because it's the best reflector but in industry probably aluminum is used since it's much cheaper. They texture the backside of the silicon first with a chemical (KOH), then deposit a passivation layer then the oxide layer then the metal. The oxide/metal is also dual-purposed as a current collector (the aluminum would be soldered to the wire carrying current away).

See here: https://aip.scitation.org/doi/full/10.1063/1.4772975

The reason metal alone is not so great is it absorbs light, especially IR, when it is textured (plasmons in the features). Texture is used because we want diffuse reflection not specular to maximize absorption and allow for most cell thinning - save on weight, material cost, also improves efficiency. Metal is great when flat and specular reflection is desired, but since we texture and metal is now lossy in this situation we insert the oxide first, the low index oxide layer totally internally reflects most light at non-normal angles (acts similar to a fiber optic cable here), at normal angles oxide still reflects a good amount of light losslessly, and then only some light reaches the metal which is kind of used as the last resort since it's lossy.

White paint would eliminate the need to texture since it causes diffuse reflection on its own. It's not used yet since we don't know if it will beat out the current technology in the long run but it's interesting and we've looked at it a few times. See some research about it here: https://www.sciencedirect.com/science/article/pii/S0927024816300022#f0005 "0.8 mA/cm2 additional [current] compared to silver mirror due to simple white paint"
 

sfsuphysics

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Who wouldn't want to save on their electricity bill by having a lighter colored roof?

The trick is that there are seasons. Most places in the US have seasons that require heating and seasons that require cooling. You'd have to compare the financial benefit in the warm season to the financial penalty in the cold season to see if this works well, unless you want to change colors twice a year :p
The thing with seasons the Sun is hitting from different angles. Light roof for summer when the sun is high in the sky to reflect light, darker walls so when sun is lower in the winter absorbs more light, best of both worlds.
 

serpretetsky

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This topic used to be my job so I'll try not to go overboard here but they do. In the research world they're a bit ahead of industry in terms of design but I believe most crystalline solar cell panels you buy will use a textured mirror made from a two-layer stack of first conductive oxide like ITO or ZnO then with metal. In lab we use silver because it's the best reflector but in industry probably aluminum is used since it's much cheaper. They texture the backside of the silicon first with a chemical (KOH), then deposit a passivation layer then the oxide layer then the metal. The oxide/metal is also dual-purposed as a current collector (the aluminum would be soldered to the wire carrying current away).

See here: https://aip.scitation.org/doi/full/10.1063/1.4772975

The reason metal alone is not so great is it absorbs light, especially IR, when it is textured (plasmons in the features). Texture is used because we want diffuse reflection not specular to maximize absorption and allow for most cell thinning - save on weight, material cost, also improves efficiency. Metal is great when flat and specular reflection is desired, but since we texture and metal is now lossy in this situation we insert the oxide first, the low index oxide layer totally internally reflects most light at non-normal angles (acts similar to a fiber optic cable here), at normal angles oxide still reflects a good amount of light losslessly, and then only some light reaches the metal which is kind of used as the last resort since it's lossy.

White paint would eliminate the need to texture since it causes diffuse reflection on its own. It's not used yet since we don't know if it will beat out the current technology in the long run but it's interesting and we've looked at it a few times. See some research about it here: https://www.sciencedirect.com/science/article/pii/S0927024816300022#f0005 "0.8 mA/cm2 additional [current] compared to silver mirror due to simple white paint"
i see. why does diffuse reflected light work better?
 

Kalessian

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i see. why does diffuse reflected light work better?

The solar cell is much much wider than is it thick (15 cm vs 0.015 cm), so if you can scatter the light sideways as much as possible it will get 'trapped'. Models (some of them are ray tracing models :) guess I need work to pay for my next RTX) show that a perfectly diffuse reflector (Lambertian) while not always scattering light at wide angles (some light is scattered straight up) it is hard to beat when considering all the wavelengths and angles of incoming light that a solar panel will have to deal with. Flat white paint is pretty close to lambertian. Though this area is actively researched and people are trying to do better with all sorts of exotic scattering schemes.

For more info look at the very bottom interactive plot on this page (click to start): https://www.pveducation.org/pvcdrom/design-of-silicon-cells/light-trapping and then here https://www.pveducation.org/pvcdrom/lambertian-rear-reflectors
 

serpretetsky

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The solar cell is much much wider than is it thick (15 cm vs 0.015 cm), so if you can scatter the light sideways as much as possible it will get 'trapped'. Models (some of them are ray tracing models :) guess I need work to pay for my next RTX) show that a perfectly diffuse reflector (Lambertian) while not always scattering light at wide angles (some light is scattered straight up) it is hard to beat when considering all the wavelengths and angles of incoming light that a solar panel will have to deal with. Flat white paint is pretty close to lambertian. Though this area is actively researched and people are trying to do better with all sorts of exotic scattering schemes.

For more info look at the very bottom interactive plot on this page (click to start): https://www.pveducation.org/pvcdrom/design-of-silicon-cells/light-trapping and then here https://www.pveducation.org/pvcdrom/lambertian-rear-reflectors
oh snap! This will be my last question since I'm starting to go pretty far off-topic. Assuming you DO know the angle of incoming light (solar panel has tracking system to always point straight at the sun for example), is it still better to have a randomized diffuse rear reflector or at the point does some other reflection / refraction system work better?
 

DukenukemX

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White paint that acts like an air conditioner? If you believe that then a reflective surface would be like the north pole.
 

Kalessian

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oh snap! This will be my last question since I'm starting to go pretty far off-topic. Assuming you DO know the angle of incoming light (solar panel has tracking system to always point straight at the sun for example), is it still better to have a randomized diffuse rear reflector or at the point does some other reflection / refraction system work better?

Debated by researchers because sunlight is still broadband and it's tough to get a reflection scheme that can target more than a narrow wavelength band and maintain at or above Lambertian effectiveness. See here for more on the topic: https://doi.org/10.1021/nn300287j

If you want my opinion I personally believe we can do better than random but only because truly random Lambertian reflection is a myth in my eyes and we can never truly achieve what the random models predict so it's a false benchmark.

Look here for a very exotic\novel optimization method: https://arxiv.org/abs/2008.04781 Possibly AI could be used to find the 'perfect' structure for any given use-case.
 
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All this Black and White, and not one mention of:

"By adding this product to your cart you confirm that you are not Anish Kapoor, you are in no way affiliated to Anish Kapoor, you are not purchasing this item on behalf of Anish Kapoor or an associate of Anish Kapoor. To the best of your knowledge, information and belief this paint will not make its way into that hands of Anish Kapoor."

Son, I am Disappoint
 

Krenum

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For all the tree huggers out there, wouldn't reflective paint just reflect solar radiation back into the atmosphere and heat it up?
 

Axman

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For all the tree huggers out there, wouldn't reflective paint just reflect solar radiation back into the atmosphere and heat it up?

Even if it worked in a 1:1 ratio like that, it would still be more efficient than using energy to pump heat out of a building than it does to prevent it from getting in.

Also I don't think it works like that. It would have to be captured by the atmosphere, when a lot of it will just radiate all the way back out to space. I should think. I'm sure clouds, haze, upper atmospheric hijinks, and the word albedo all come into play, but I'm not a climatiatrist.
 

LukeTbk

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For all the tree huggers out there, wouldn't reflective paint just reflect solar radiation back into the atmosphere and heat it up?

There would be some loss I think, there is a reason that ice age are a reinforcing colding circle because the snow reflect almost all the heat back..
 
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