'Whitest ever' paint reflects 98% of sunlight • Hacker News Board

Re: 'Whitest ever' paint reflects 98% of sunlight

#251

Post by mannykannot » Sat, Apr 17, 2021, 2:06 AM UTC

cryptonector wrote: post #213

mannykannot wrote: post #200

"An infrared camera (right image) shows how a sample of the whitest white paint (the dark purple square in the middle [of the infrared image]) cools the board below ambient temperature." So... Maxwell's demon?

Well, if something can only radiate, and will absorb much less than it radiates... the only way it could stay at ambient temperature would be via contact transmission. I would expect an object painted in this whitest paint to cool below ambient temperature unless it had a heater inside it, say, or unless it was submerged in water rather than air.

The thing is, though, if you put such a substance in a dark vacuum, what's to stop it cooling to absolute zero?

The process of electromagnetic radiation is the inverse of electromagnetic absorption, and so what will happen here is that the sample will reach a state of thermal equilibrium with the walls of its container (or the 2.7K cosmic background radiation if we're in deep space) through the exchange of infra-red radiation. If it went to a lower temperature, we could create a perpetual motion machine by putting a thermocouple between the painted object and its container.

It is possible to cool some things with radiation, but that requires creating a state that is not in thermal equilibrium, which is not plausible for paint on a wall.

https://en.wikipedia.org/wiki/Laser_cooling

Re: 'Whitest ever' paint reflects 98% of sunlight

#252

Post by aidenn0 » Sat, Apr 17, 2021, 2:11 AM UTC

FredPret wrote: post #153

earthscienceman wrote: post #128

Earlier quoted context omitted.

Geo-engineering is an extremely flawed way to approach the climate change problem, for a million reasons including this one.

The Nazi’s had an idea of launching a sun gun (Sonnengewehr) made of sodium metal I think. It would then fry the Allies with focused sunbeams. They were also on meth by the way. However maybe we could build a bunch of similar mirrors in the Earth-Sun L1 Lagrange point (reflecting light straight back at the Sun of course!)

A few trillion small reflective solar sails (for station keeping) at L1 would do it[1]. Someone should tweet at musk to get approximate launch costs for that.

1: https://en.m.wikipedia.org/wiki/Space_sunshade

Re: 'Whitest ever' paint reflects 98% of sunlight

#253

Post by FredPret » Sat, Apr 17, 2021, 2:16 AM UTC

aidenn0 wrote: post #252

FredPret wrote: post #153

Earlier quoted context omitted.

The Nazi’s had an idea of launching a sun gun (Sonnengewehr) made of sodium metal I think. It would then fry the Allies with focused sunbeams. They were also on meth by the way. However maybe we could build a bunch of similar mirrors in the Earth-Sun L1 Lagrange point (reflecting light straight back at the Sun of course!)

A few trillion small reflective solar sails (for station keeping) at L1 would do it[1]. Someone should tweet at musk to get approximate launch costs for that. 1: https://en.m.wikipedia.org/wiki/Space_sunshade

That number sounds nuts but it only adds up to 20 million tonnes. Actually, that sounds even more nuts.

But if you can grab the 20 million tons from asteroids, maybe it's achievable.

Re: 'Whitest ever' paint reflects 98% of sunlight

#254

Post by hashkb » Sat, Apr 17, 2021, 3:57 AM UTC

dcanelhas wrote: post #224

Duralias wrote: post #134

Earlier quoted context omitted.

Maybe not more, but different wavelengths. The Wikipedia page does say "The purpose of the colour was to reflect some of the thermal radiation from a nuclear explosion", as far as my experience goes polished metal can still get extremely hot.

Indeed, a friend of mine who designs playgrounds told me that one of her constraints is for slides not to be oriented such that they heat up too much from the sun.

I swear when I was a kid the rules must have been different. Every metal slide was always hot enough to fry bacon.

Re: 'Whitest ever' paint reflects 98% of sunlight

#255

Post by robomartin » Sat, Apr 17, 2021, 5:31 AM UTC

readflaggedcomm wrote: post #241

robomartin wrote: post #144

Yeah, no, 98% percent reflectance paint has been available for, I don’t know, 30 years. I was using it about 15 years ago for a product that required high optical efficiency. The problem with such paints or coatings is that they don’t perform well over time outside of a clean room environment. On a roof this 98% would likely only exist for 1.2 microseconds. Dust, dirt, aging an bird shit will make sure of that. Clima…

I agree. But theoretically, if the paint shed or repelled dirt very well, it could outperform something with near the same reflectivity. But the article doesn't acknowledge titanium dioxide paints with the same theoretic reflectivity, so I have to assume it won't perform any better than existing products.

Well, the premise of the article is preposterous just the same. Reflective roofs are not going to save the planet. I sure hope that's not what they pitched to get funding for this research.

It would be a waste of money on multiple fronts:

- Super-reflective materials and coatings already exist.

- They don't perform well at all outside of very well controlled environments.

- To repeat myself, the idea that reflective roofs are going to even represent a rounding error in the climate change equation is nothing short of delusional.

They might even cause more harm than good.

- And then there's the same set of questions that should be applied to every single magical climate change solution: How much CO2 will be produced making it? How much energy will it take? How many other pollutants are we going to generate and disperse? What is the resource equation for the entire life cycle, from manufacturing, through application, maintenance and eventual replacement?

Re: 'Whitest ever' paint reflects 98% of sunlight

#256

Post by SergeAx » Sat, Apr 17, 2021, 6:59 AM UTC

trhway wrote: post #236

SergeAx wrote: post #233

Earlier quoted context omitted.

You would need pure zink (obtained in ~1750) and pure acid to implement voltac pile. You would need copper wire to implement telegraph.

you don't need pure acid. Vinegar of high concentration would do great. >You would need pure zink (obtained in ~1750) https://en.wikipedia.org/wiki/Roman_metallurgy#Types_of_meta... "By the height of the Roman Empire, metals in use included: silver, zinc, iron, mercury, arsenic, antimony, lead, gold, copper, tin" >You would need copper wire to implement telegraph copper is very pliable, so it is easy to make wires.

Zink was used by ancient Greeks and Romans in a brass alloy. Zink and copper are interchangeable in a crystal structure of brass, and are inseparable because of that. Obviously, brass is useless in voltac pile because of copper in it.

I am not that sure about vinegar as a medium. I beleive it will lead to low voltage and weak power, rendering the pile useless for long distance transmission.

The same applies to copper wire. You need steel to draw copper to make wire, otherwise wires will be short, need to be soldered and become ineffective for long distance.

Also, telegraph lines are too easy to sabotage. Fire signals are much more reliable to rule ancient empire.

Re: 'Whitest ever' paint reflects 98% of sunlight

#257

Post by dredmorbius » Sat, Apr 17, 2021, 6:59 AM UTC

ping_pong wrote: post #199

This sounds like a waste of energy to me. I think all roofs should be covered in solar power generating equipment. Reflecting all that sun energy back into the air just heats up our planet, better to convert that into electricity

Both have their merits. It depends on what's needed in a specific location, how much incident sunlight there is, and what the effects on other cooling loads are.

By reflecting white light back through the atmosphere, rather than absorbing light and re-radiating heat (infrared) wavelengths, more energy can be transmitted back through and out of the atmosphere into space. Air, and specifically the CO2 and other greenhouse gasses in it, are relatively opaque to infrared light, so that is trapped.

In areas with high cooling loads, offsetting heat before it can enter into structures has benefits. This is reflective rather than insulative blocking, and is quite effective.

Solar panels are of course useful, though expensive compared with even specialty paints. They also convert most of the incident sunlight to heat (only about 10-20% is typically converted to electricity), which is re-radiated into surroundings. Again, typically this isn't a major factor, but it could well be worthwhile painting surfaces not covered with PV arrays white, especially in warm climates and high-solar-incidence regions.

I have my doubts whether this specific paint's characteristics are all that meaningful in a real world with dust, dirt, grime, and bird droppings. But the underlying idea is valid and has been used in similar technologies and deployments.

Re: 'Whitest ever' paint reflects 98% of sunlight

#258

Post by hulitu » Sat, Apr 17, 2021, 8:48 AM UTC

DanBC wrote: post #217

blacksqr wrote: post #96

Earlier quoted context omitted.

They used standard acrylic paint manufacture techniques, just substituting barium sulfate for the usually-used white pigment titanium dioxide. So most such questions should be answered simply by looking at previous experience with existing white acrylic paint.

So, in about 10 years we're going to have yet another source of trillions of particles of microplastic?

Titanium dioxide and barium sulfate is not plastic. They are anorganic compounds.

Re: 'Whitest ever' paint reflects 98% of sunlight

#259

Post by DanBC » Sat, Apr 17, 2021, 11:48 AM UTC

hulitu wrote: post #258

DanBC wrote: post #217

Earlier quoted context omitted.

So, in about 10 years we're going to have yet another source of trillions of particles of microplastic?

Titanium dioxide and barium sulfate is not plastic. They are anorganic compounds.

The other ingredient of acrylic paint is an acrylic polymer.

Re: 'Whitest ever' paint reflects 98% of sunlight

#260

Post by loonster » Sat, Apr 17, 2021, 2:30 PM UTC

DanBC wrote: post #259

hulitu wrote: post #258

Earlier quoted context omitted.

Titanium dioxide and barium sulfate is not plastic. They are anorganic compounds.

The other ingredient of acrylic paint is an acrylic polymer.

That will not increase plastic in the environment unless the new paint is less durable or incentivizes painting previously unpainted surfaces.