ysabetwordsmith (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
ysabetwordsmith) wrote2020-10-11 02:11 pm
ysabetwordsmith) wrote2020-10-11 02:11 pm
Entry tags:
Radiative Cooling
My partner read me an article about SkyCool Systems, which has invented a film that can do passive cooling by radiating energy out into space. It has some very interesting potential, although pinning down some important aspects is a challenge.
* My first question was, "What's the limiting ingredient?" Because most fancy science tricks are done with rare earths or something else in short supply, which minimizes the scalability. (Peak lithium could screw us a lot harder than peak oil, but that's only one example.) But later in the article it mentioned the eerie effect of touching something cold on a hot day, and I've actually had that experience in White Sands. The gypsum not only didn't heat in the sun, it cooled a foot or two of air above it, creating a bizarre tangible gradient. Gypsum is common as dirt, so if that's the key ingredient, the technology is much more scalable than if it relies on rare earth(s). Alas, I could not pin down the ingredients used to make the film, so this aspect remains unknown.
* It uses nanotech. It's possibly the most responsible use of that technology I've seen yet. However, nanotech is ruinously expensive at this state of development; it doesn't get cheap until rather later. This limits applications in places where it's needed most, like developing nations. We'll have to wait and see what economies of scale can do for it.
* It's billed as passive cooling. Now, it can work that way, just by itself. But the system they're promoting most is actually an active cooling system that pipes water through tubes under the panel, which cools the water and thus makes an attached air conditioner more efficient. You don't need energy to make the panel work, but you do to move the water -- which means probably electricity. You could pump with animal or human power, but most places don't do that anymore. Always read the fine print. Me, I'd try the actually passive version as a shade to minimize heating of parking spaces. Hell, it'd be useful just as a heat pump to get thermal energy the fuck off this planet.
They're also exploring some other things. One uses heat differential to make light. Now, we've had variations of this one in the past, generating energy from heat differentials; cute trick but it's a side step. If the claim is accurate that the film radiates energy into space -- if they're taking heat waves and altering the wavelength so they actually leave the atmosphere instead of just hanging around in the air -- then they just did the hardest part of treating the electromagnetic spectrum as a slinky. The most useful application for that is actually in killing waste heat, which is a big problem in some industries and will get worse as global warming drives up the temperatures. If you could turn waste heat into something harmless or even useful, instead of merely moving it around or using it as raw material for the next factory, that would be an enormous help. Of course, if you can manipulate wavelengths, you can also change nonvisible waves into visible waves directly. The most efficient way to do that is to find a material that naturally squeezes or stretches the slinky, like this film is described doing, only for visible light you need different output ranges.
Bear in mind that manipulating the electromagnetic spectrum -- not just using accessible parts of it, but directly squeezing or stretching it to make it do what you want -- is a keystone technology of advanced spacefaring civilizations. Usually you start out with starships using radiators to dump waste heat into space, rather than recapturing it to make desirable energy, which is a much cruder use of radiative heating. And if the articles are accurate, then these guys just did the hard thing on a planet. Damn. That's impressive. Once you've got the concept "energy is a slinky" then iterating that to other exchanges is fairly straightforward; you just need to hunt for materials and/or shapes that change an unwanted bandwidth into a wanted bandwidth along different ranges.
* My first question was, "What's the limiting ingredient?" Because most fancy science tricks are done with rare earths or something else in short supply, which minimizes the scalability. (Peak lithium could screw us a lot harder than peak oil, but that's only one example.) But later in the article it mentioned the eerie effect of touching something cold on a hot day, and I've actually had that experience in White Sands. The gypsum not only didn't heat in the sun, it cooled a foot or two of air above it, creating a bizarre tangible gradient. Gypsum is common as dirt, so if that's the key ingredient, the technology is much more scalable than if it relies on rare earth(s). Alas, I could not pin down the ingredients used to make the film, so this aspect remains unknown.
* It uses nanotech. It's possibly the most responsible use of that technology I've seen yet. However, nanotech is ruinously expensive at this state of development; it doesn't get cheap until rather later. This limits applications in places where it's needed most, like developing nations. We'll have to wait and see what economies of scale can do for it.
* It's billed as passive cooling. Now, it can work that way, just by itself. But the system they're promoting most is actually an active cooling system that pipes water through tubes under the panel, which cools the water and thus makes an attached air conditioner more efficient. You don't need energy to make the panel work, but you do to move the water -- which means probably electricity. You could pump with animal or human power, but most places don't do that anymore. Always read the fine print. Me, I'd try the actually passive version as a shade to minimize heating of parking spaces. Hell, it'd be useful just as a heat pump to get thermal energy the fuck off this planet.
They're also exploring some other things. One uses heat differential to make light. Now, we've had variations of this one in the past, generating energy from heat differentials; cute trick but it's a side step. If the claim is accurate that the film radiates energy into space -- if they're taking heat waves and altering the wavelength so they actually leave the atmosphere instead of just hanging around in the air -- then they just did the hardest part of treating the electromagnetic spectrum as a slinky. The most useful application for that is actually in killing waste heat, which is a big problem in some industries and will get worse as global warming drives up the temperatures. If you could turn waste heat into something harmless or even useful, instead of merely moving it around or using it as raw material for the next factory, that would be an enormous help. Of course, if you can manipulate wavelengths, you can also change nonvisible waves into visible waves directly. The most efficient way to do that is to find a material that naturally squeezes or stretches the slinky, like this film is described doing, only for visible light you need different output ranges.
Bear in mind that manipulating the electromagnetic spectrum -- not just using accessible parts of it, but directly squeezing or stretching it to make it do what you want -- is a keystone technology of advanced spacefaring civilizations. Usually you start out with starships using radiators to dump waste heat into space, rather than recapturing it to make desirable energy, which is a much cruder use of radiative heating. And if the articles are accurate, then these guys just did the hard thing on a planet. Damn. That's impressive. Once you've got the concept "energy is a slinky" then iterating that to other exchanges is fairly straightforward; you just need to hunt for materials and/or shapes that change an unwanted bandwidth into a wanted bandwidth along different ranges.
Thoughts
Fascinating!
>> because to double the frequency you half the wavelength, <<
I remember that from music.
>> and short wavelength Infra-red isn't absorbed by the atmosphere, it goes straight out into space. It's also the principle heating element of sunlight, as it's absorbed by objects, and re-radiated as longer wavelength IR, which is absorbed by air [and greenhouse gasses.] <<
Okay, so we could take this initial example and generalize it to look for ways that turn LWIR to SWIR. It doesn't need to be incorporated into active cooling systems. My target would be durable materials that could be used to surface roads, roofs, parking lot shades, etc. thus turning heat absorbers into heat disposals.
Another approach would be looking for a transparent version that could be cast into or filmed over windows to prevent them from turning buildings into greenhouses. Like the search for a lightbulb filament, it might take 10,000 attempts to find what works, but the payoff would be enormous.
>> As you say, it's a very impressive trick. Now we need a few billion square miles of the stuff.<<
If it's made with gypsum or something else common, we could do that. If it's like rare-earth supermagnets, then we couldn't. But we could certainly investigate the radiative properties of common materials to find the ones with useful exchanges. No telling what you'll get on any given planet, but there's usually something good.
So far, most of what I've seen has involved pale reflective coatings to bounce the light off of surfaces so it doesn't absorb and turn into heat. That alone has a lot of potential if we could turn blacktop and tar roofs from absorption to reflection. But it would be better if we could channel the waves OUT of the atmosphere.
Also, I'd like to see humans focus on a technology that is less destructive. Spectral manipulation can be weaponized, but it's really tedious to figure out how. The industrial applications are many, profitable, and easier to find. Given how badly we need heat dumpers right now, that would be constructive motivation. I just hope they don't fuck around for several decades like they did with solar panels.
Re: Thoughts
Well, I'd want to check what they're doing with it first, and how environmentally friendly it is... but imagine a few billion tons of this film, turned into glitter, and blasted up into the troposphere, cooling the earth. Although hopefully not too much.. I've seen Snowpiercer, that's not a future I'd fancy.
Failing that, a big sheet of it for the ice-caps.
IIRC there are crystals that are very good at turning LWIR into SWIR, I don't know exactly how easy they are to make, but they are made of pretty common stuff. But they have this neat trick of whatever way the light enters them, that's the direction it's bounced back, kinda like a radar corner. You could make a powder or paint of that, and just apply it where you need cooling.
Re: Thoughts
Yeah, I was concerned about the environmental impact, but unless it's awful they probably come out ahead.
>> but imagine a few billion tons of this film, turned into glitter, and blasted up into the troposphere, cooling the earth. Although hopefully not too much.. I've seen Snowpiercer, that's not a future I'd fancy.<<
I absolutely do not trust humans with geoengineering. They don't understand enough about how the planet works, and they don't give a flying fuck about it.
>> Failing that, a big sheet of it for the ice-caps.<<
That's a thought.
>> IIRC there are crystals that are very good at turning LWIR into SWIR, I don't know exactly how easy they are to make, but they are made of pretty common stuff. But they have this neat trick of whatever way the light enters them, that's the direction it's bounced back, kinda like a radar corner. You could make a powder or paint of that, and just apply it where you need cooling. <<
Very useful. We could use that to coat buildings, roofs, sunshades -- if it's durable or can be incorporated into things, pavement too.