Comment by coolradmab | Hacker News Reader

Comment by coolradmab | Hacker News Reader

I've been actively working on this technology, goal is making it cheaper and simplify installation. Stanford's a highly reflective surface ~95% combined with stacks layers of silica oxide on a wafer under vacume. The trick too achieving bellow ambient temperature is too reflect nearly all solar energy while emitting strongly in the "atmospheric window". Most silica compounds are well suited as emitters, however the hard part is adding a reflector too the silica and minimising heat transfer from the environment. I've managed to make a meta material paint, reflector and emmiter that achieved bellow ambient temperature, with bulky conventional insulation. as for any effective cooling bellow ambient.

Radiative cooling is just not that strong of heat transfer, what you want too look our for is the research into reflective coatings needrthese systems too function. Review paper: https://www.sciencedirect.com/science/article/pii/S030626191... Shameless plug: https://www.scihouse.space

I'm eager to experiment with a material like this for the application of passive water harvesting in a high humidity environment.

Would you be able to recommend some materials that are perhaps sub-optimal for the task but trivial to assemble from commodity sources to produce this effect?

Silica better yet a net http://nnf.mit.edu/sites/default/files/publications/files/GH...

wouldn't large scale usage of a device like this essentially increase the planetary albedo and help fight climate change? especially if you just skip the "environmental heat transfer" part

Short answer not really https://what-if.xkcd.com/84/

That's more a "we haven't made enough paint to cover a large fraction of the planet" argument than a "what would the thermal ramifications of such an act be" argument. Which I was excited to read about, but alas.

You would need a really big roller with a lot of knap too. Although I suppose you could paint most of the midwest and avoid the mountains with a flatter roller.

For an interesting toy model related to this, check out Lovelock's Daisyworld simulation:

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

The argument (and the related Gaia hypothesis) has some important and subtle connections to the facts of climate change. Though even if it's correct, and the biosphere will tend to naturally reassert homeostasis, there's no guarantee we'll enjoy living through it.

This makes me think: Earth's energy imbalance is around 0.5W/m2, while such a paint sends how much, 40W/m2 through the transparency window?

So we'd only have to paint 1/80 of the Earth. That's ~6.4mln km2, or 2/3 the area of the USA. Still a lot, but not impossible.

I'm sure paint manufacturing scales better than li-ion batteries, and those more than doubled in production volume over the last decade.

Interesting, but even if we solved the temperature problem, we would still have the issue of the acidification of the oceans due to excess CO2. In the end we must remove CO2 from the atmosphere one way or another.

All that would do is offset things so that we can pollute more. Not to mention the CO2 and other emissions from such a project. And it would ruin a huge amount of space because of course this would run into “not in my neighborhood”. It’s far better to fix the problem than to paint over it.

There's some numbers here for what it would take.

https://www.cell.com/joule/pdf/S2542-4351(19)30354-X.pdf

Basically we need 1W/m^2 of cooling for the earth, so if you could get a radiative cooling device with 100W/m^2 you'd need to cover about 1% of Earth's area

I assume the actual radiative power is greater than the cooling capability, since cooling power = radiative power - heat intake from atmosphere - heat intake from sun

so the math works out even better than it seems...?

Let's say human inhabit roughly 10% of Earth surface. If we cover all rooftops in the world, that ought to make some effect yeah?

I'm really ignorant about this whole field.

Your work on passive radiative cooling doesn't sound like biotech or related to biotech but your link https://www.scihouse.space is a biotech lab.

I was just wondering the kind of education/knowledge someone who is working on the cooling technology would have, and was surprised to see a biotech background. So am wondering on the journey to get from biotech to whatever is needed for the cooling tech.

Getting past the mental barrier that engineer's and biologist don't get along. Manipulation of micro structures needed to develop meta materials are on sale that biological systems function at. May have come from a classic engineering of wood and steel, but throw in a foam here and a self-assembling structure there and you can make things no amount of carbide inserts and glue would ever get you.

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