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> 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.
Since we're talking about stirling engines, I've always wondered how using geothermal heat for a larger stirling engine would work. https://youtu.be/duuk_r--lqU?t=99 Even though the video uses the sun to heat the oil, I would think it would be feasible to use geothermal heat instead.
https://en.wikipedia.org/wiki/Organic_Rankine_cycle
> 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.
Nothing to sneeze at. Just be careful of midbrow high-effort dismissals from the old and wise:)
These guys are applying them to solar panels:
https://www.i2cool.com/tideflow/uwJVdixI.html
"Case Study 2: Solar Farm in Dubai
Problem: Solar panels lost 15–20% efficiency at 55°C+ temperatures.
Solution: Coated panels with i2Cool’s film.
Results:
Panel surface temperature: ▼25.7°C (from 58°C to 32.3°C)
Power output: ▲8% (equivalent to adding 2,400 new panels to a 30MW farm)"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
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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…
The product datasheet[0] claims a thermal emittance (aka LWIR) of 0.82. Having such a high value is typical for non-metallic surfaces.[1]
[0] https://5.imimg.com/data5/CA/RO/MY-653008/excel-cool-coat.pd...
[1] https://ntrs.nasa.gov/api/citations/19840015630/downloads/19...
Slightly off-topic - I was momentarily excited this was a replication of https://journals.aps.org/prapplied/abstract/10.1103/PhysRevA... (Electric Power Generation from Earth’s Rotation through its Own Magnetic Field) I've been stalking the citations for this paper for a while now. Surely people would be scrambling to replicate these results. It could truly be transformative for the world if it works and is scale-abl…
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Yes, but it works at night! Not sure if you can get the MTBF on Stirling engines higher than on LFP batteries, though.
And in the day time, if transparent and applied to solar panels, the "efficiency" gain (~10W psqm) itself will dwarf other considerations.( Remembering that bulk of radiative cooling shouldn't happen below ~1300nm) And then there's beating the efficacy of carbon capture at mitigating warming by orders of magnitudes Nothing to sneeze at. Just be careful of midbrow high-effort dismissals from the old and wise:) These g…
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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…
To be fair it does say "reflects solar infrared rays," which I would interpret as "the IR from the Sun" (aka NIR). The product datasheet[0] claims a thermal emittance (aka LWIR) of 0.82. Having such a high value is typical for non-metallic surfaces.[1] [0] https://5.imimg.com/data5/CA/RO/MY-653008/excel-cool-coat.pd... [1] https://ntrs.nasa.gov/api/citations/19840015630/downloads/19...
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IIRC, the papers they're working from mention that lime works very nearly as well as the baryta they're using. Guess what people have been painting their houses white with for several thousand years?
Not with the optimal mixture for maximum-packing of limestone nanospheres. That effect is almost not perceptible in normal milled limestone.
I totally believe that you can get significant percentage improvements with the right mix of particle sizes, but the LWIR emittance of just about all nonmetals was upwards of 75% the emittance of an ideal blackbody. That puts a ceiling of about ⅓ (4:3) on the possible improvement on that end. And plain old whitewash has a reflectivity upwards of 90% in the visible, while the best known materials, such as polished silver, are something like 96%, so you might get 3:2 on that end—but probably won't even get 2:1. https://nvlpubs.nist.gov/nistpubs/bulletin/07/nbsbulletinv7n... is one older reference on this, but https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=90... gives plots of silver mirrors' reflectance by wavelength, polarization, and angle of incidence.
As a side note, what people have been painting their houses with for thousands of years isn't normal milled limestone; it's slaked lime, which forms limestone by absorbing CO₂ from the air over about a month. Modern whitewash has milled limestone mixed into it, but the morphology of the final surface isn't very similar to milled limestone in a transparent binder.
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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 beyon…
You should be aware that there are rigorous constraints on how much absorptance can differ from emittance, known as Kirchhoff's Law of Thermal Radiation: https://en.wikipedia.org/wiki/Emissivity#Absorptance because without them you could get mechanical power generation from a uniform bath of thermal radiation, which would give you a perpetual-motion machine.