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Mechanical power generation using Earth's ambient radiation

science.org

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Re: Mechanical power generation using Earth's ambient radiation

#41

Post by kragen »

kumarvvr wrote: post #23
jcims wrote: post #14

DIY radiative cooling paint from YouTuber NightHawkInLight - https://www.youtube.com/watch?v=N3bJnKmeNJY&list=PL1a2HkcVbm... It has pretty impressive performance. Tech Ingredients did one or two vids as well - https://www.youtube.com/watch?v=dNs_kNilSjk Was thinking of whipping up a batch for my rv.

This concept is used all over India to cool down homes that are on the top floors. https://www.amazon.in/EXCEL-CoolCoat%C2%AE-Reflective-Coatin... Basically, have a highly reflective white coat on your roof, to reduce temperatures by about 3 Degrees Celsius. Almost all homes in Urban India are made from concrete and bricks, which can hold a lot of heat. I myself have been in houses that use this to cover only some ro…

This is the opposite. It says, "Refelects [sic] 90% of solar infrared rays," because of its "High IR reflective Pigments [sic]," so its emissivity in the infrared is 0.1, but the IR-selective paints we're talking about here are optimized for high infrared emissivity, which means they absorb a lot of infrared.

Maybe there's some wiggle room here because solar infrared is mostly near IR and MWIR, and the place where we want high emissivity (absorptivity) is longwave IR, but to the extent that the advertisement makes any claims about infrared emissivity, it claims very low infrared emissivity, not high.

A paint with low emissivity across the spectrum will slow down the temperature rise when the sun is up, but also slow down the temperature drop when the sun is down. This can still make rooms livable, but it isn't the same as what you get with regular whitewash, where the temperature of the roof is actually lower than the temperature of the air around it.

Re: Mechanical power generation using Earth's ambient radiation

#42

Post by kragen »

Animats wrote: post #30

> 400 milliwatts per square meter About two orders of magnitude weaker than solar panels, even over 24 hours. E = (T2-T1) / T2

Yes, but it works at night!

Not sure if you can get the MTBF on Stirling engines higher than on LFP batteries, though.

Re: Mechanical power generation using Earth's ambient radiation

#43

Post by WJW »

andbberger wrote: post #26
nine_k wrote: post #24

Earlier quoted context omitted.

This can't be correct. 10,000 TWh/y = 1e+7 GWh/y, divide it by 365.25 days/y to produce daily output of 27,379 GWh/day, then by 24 h/day to get pure power of 1,141 GW. It's still more than a terawatt, three orders of magnitude larger than the largest nuclear reactors.

oops. yes. still not that much though. i mean it's a lot but it's "one more large industrialized country" a lot not "kardashev 2" a lot

Kardashev 2 has a Dyson sphere. Of course anything on a single planet can never have that much.

Re: Mechanical power generation using Earth's ambient radiation

#44

Post by sigmoid10 »

wombatpm wrote: post #33
cameldrv wrote: post #29

Not an engine, but some friends of mine got a mylar sheet that's black on one side and reflective on the other. We tried it out in the desert tied onto trees/vehicles. You put the shiny side down, so the hot IR radiation of the earth is reflected away, and the black side sees the extremely cold (in IR) desert sky. If you put a little hole in the middle and put a bucket under it, you get a fair bit of water, because t…

Now you just need a couple of droids and you could go into the moisture farming business

What I really need is a droid that understands the binary language of moisture vaporators.

Re: Mechanical power generation using Earth's ambient radiation

#45

Post by scoopertrooper »

Animats wrote: post #30

> 400 milliwatts per square meter About two orders of magnitude weaker than solar panels, even over 24 hours. E = (T2-T1) / T2

>400 milliwatts per square meter of mechanical power with a potential for >6 watts per square meter.

Re: Mechanical power generation using Earth's ambient radiation

#46

Post by timdiggerm »

sigmoid10 wrote: post #44
wombatpm wrote: post #33

Earlier quoted context omitted.

Now you just need a couple of droids and you could go into the moisture farming business

What I really need is a droid that understands the binary language of moisture vaporators.

But can he speak Italian lawn games?

Re: Mechanical power generation using Earth's ambient radiation

#48

Post by nickdothutton »

cameldrv wrote: post #29

Not an engine, but some friends of mine got a mylar sheet that's black on one side and reflective on the other. We tried it out in the desert tied onto trees/vehicles. You put the shiny side down, so the hot IR radiation of the earth is reflected away, and the black side sees the extremely cold (in IR) desert sky. If you put a little hole in the middle and put a bucket under it, you get a fair bit of water, because t…

I think I read something similar in a "Boys survival book, desert chapter" in the early 80s.

Re: Mechanical power generation using Earth's ambient radiation

#49

Post by jcims »

kragen wrote: post #41
kumarvvr wrote: post #23

Earlier quoted context omitted.

This concept is used all over India to cool down homes that are on the top floors. https://www.amazon.in/EXCEL-CoolCoat%C2%AE-Reflective-Coatin... Basically, have a highly reflective white coat on your roof, to reduce temperatures by about 3 Degrees Celsius. Almost all homes in Urban India are made from concrete and bricks, which can hold a lot of heat. I myself have been in houses that use this to cover only some ro…

This is the opposite. It says, "Refelects [sic] 90% of solar infrared rays," because of its "High IR reflective Pigments [sic]," so its emissivity in the infrared is 0.1, but the IR-selective paints we're talking about here are optimized for high infrared emissivity, which means they absorb a lot of infrared. Maybe there's some wiggle room here because solar infrared is mostly near IR and MWIR, and the place where we…

It kind of blew my mind when I first learned about this whole phenomenon (mostly from the YouTube series I posted). Not all white paints are equal and it’s kind of interesting to think that something that looks mostly identical to our eyes has very different (passive) properties in the infrared.

I think one of the things in the paints that Ben adds is a set of microspheres that reject incident incoming infrared beyond a certain angle but allow it to pass through when radiated. Something like that.

Re: Mechanical power generation using Earth's ambient radiation

#50

Post by thijson »

bilsbie wrote: post #47

I wonder if you could harness different temperatures at different water depths.

You can, it's called OTEC:

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

Just like this scheme, it's not very economically efficient.

Carnot efficiency is proportional to the temperature ratio between the hot end and the cold end in degrees Kelvin. If both temperatures are in the 200's, then efficiency will be low.

OTEC does provide lots of potable water though, so that's one advantage.

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