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I'm super ignorant on physics and whatnot; but wouldn't it make more sense to use airships covered with solar panels at 5k-6k meter altitude? Thin solar is now

I'm super ignorant on physics and whatnot; but wouldn't it make more sense to use airships covered with solar panels at 5k-6k meter altitude? Thin solar is now a thing, and I'm quite sure that there would be a viable way to engineer an airship in such a way. One could even use graphene aerogel instead of helium or hydrogen as the lighter-than-air filler. Is this a really dumb idea? Any of you with a more relevant background could tell me where this could be so wrong?

dahfizz 4y ago
Is graphene aerogel lighter than air? I thought it _was_ mostly air, which is why its so light.
- simonebrunozzi 4y ago
  About 7 times lighter than air, AFAIK.
  - SapporoChris 4y ago
    https://en.wikipedia.org//wiki/Aerographene https://en.wikipedia.org//wiki/Aerographene It is approximately 7.5 times less dense than air. Note that the cited density does not include the weight of the air incorporated in the structure: it does not float in air.
idiotsecant 4y ago
Seems like some of the bad parts of terrestrial solar (fighting atmospheric conditions, wind loading, etc) without the good parts of orbital solar (once you're in orbit, staying there is relatively easy and you have very little in the way of mechanical stresses for your solar array, so you can make it really huge). I might not be thinking about it hard enough.
LarryMullins 4y ago
> 5k-6k meter altitude That's not high enough to put you above bad weather (airliners fly higher, and they divert around storms.) Bad weather is bad news for airships and historically destroyed about as many as hydrogen fires. You'd need to bring your airships down into hangers when the weather got bad. Also, wouldn't the graphene aerogel be filled with air and be heavier than air? Aerogel doesn't just float away. Unless you mean for these to be vacuum airships, but those seem very far fetched.
- cwkoss 4y ago
  I don't know if a lighter than air brick of aerogel has ever been manufactured. Would helium in the crevices generate enough lift to make a neutrally or negatively buoyant solid? If so, I want one.
  - thehappypm 4y ago
    You can get one today, it’s called a balloon
  - AlotOfReading 4y ago
    Helium and hydrogen would immediately leak out of an aerogel.
- im3w1l 4y ago
  > Vacuum airship Wow what a fascinating idea! Just thinking out loud here, but the compressive force is proprtional to area, while the boyancy is proportional to volume. So I wonder if making it big enough would allow using some fairly standard materials. What about a cube made of 6 big (huge) sheets of some strong yet light material supported by a sort of skeleton inside? Or maybe we can use electro-static repulsion to keep it from imploding? Like how a normal balloon compresses the air inside because the rubber tries to shrink but if you had a balloon that tried to expand instead, because of say electric repulsion, or maybe something else, then it would put the air inside at lower than atmospheric pressure.
  - dvdkhlng 4y ago
    Last time I read about that, the problem seemed to be buckling [1]. E.g. if you look at Euler's critical load [2] then the pressure that a slender column can withstand just depends on the aspect ratio of the column (imagine a vacuum airship that uses internal columns to withstand the air pressure). So scaling things up means, that the column's weight has to scale proportionally with total airship volume (and the (air) pressure is a constant anyways). See also these discussions here [3]. Disclaimer: I don't claim to understand any of this. [1] https://en.wikipedia.org/wiki/Buckling https://en.wikipedia.org/wiki/Buckling [2] https://en.wikipedia.org/wiki/Euler%27s_critical_load https://en.wikipedia.org/wiki/Euler%27s_critical_load [3] https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship
DennisP 4y ago
Biggest advantage of solar in geostationary is that you get power 24/7, so you don't need a lot of storage. You're not in shadow at all except for a little bit around the equinoxes. Total uptime is 99.5%.
tzs 4y ago
There have been proposals to use things at that kind of altitude for power, but the ones I've seen have been for wind power rather than solar power. The idea is to have something that is tethered to the ground and held aloft by the winds at high altitude and that has wind turbines to generate power, which is sent back to the ground by cable. There are pretty much always strong winds over much of the US at 5k-6k meters, so such a wind power generator would provide 24 hour a day power most of the time. Here's a site showing the wind over the at around the height [1]. Click where it says "earth" in the lower left to change the height. The height is given in pressure. My link is for 500 hPa pressure which is somewhere around 5500 m. The 700 hPa option would be around 3000 m, and the 250 hPa option would be around 9000 m. Here's a site with a graph of pressure vs height if you want to know the heights for the other pressure options [2]. That graph uses kPa. 0.1 kPa = 1 hPa. The proposals I've seen I've proposed a few different things to fly. One is basically just a kite carrying turbines. Another is a parasail. Another is some sort of rotor aircraft similar to a quad drone. I believe I've also seen some that use fixed wing aircraft with propellors. The ones with the rotors or propellers would have electric motors powered from the ground that can be used to get the thing up to operating altitude, and then they switch the motors from taking electricity to drive the rotors/props to letting the wind drive the rotors/props to generate electricity. [1] https://earth.nullschool.net/#current/wind/isobaric/500hPa/orthographic=-101.50,37.23,1306/loc=-98.760,41.176 https://earth.nullschool.net/#current/wind/isobaric/500hPa/o... [2] https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html https://www.engineeringtoolbox.com/air-altitude-pressure-d_4...
- chrisdalke 4y ago
  Makani (Acquired by Google and shut down) built large airplane/kites which transmitted wind power to the ground via a tether. The engineering challenges were... intense. This was all documented extensively and this documentary summarizes all the footage they took: https://www.youtube.com/watch?v=qd_hEja6bzE https://www.youtube.com/watch?v=qd_hEja6bzE One of my favorite engineering projects and documentaries, just because of the sheer ambition and scale, and the grit of the team to keep pushing through repeated failures. Sad the project was cancelled but it makes sense given the cost and complexity.
- chriswarbo 4y ago
interroboink 4y ago
You made me smirk with the combination of "I'm super ignorant on physics" and "I'm quite sure that there would be a viable way to engineer an airship in such a way" (:
zackees 4y ago
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dahfizz 4y ago

Is graphene aerogel lighter than air? I thought it _was_ mostly air, which is why its so light.

simonebrunozzi 4y ago
About 7 times lighter than air, AFAIK.
- SapporoChris 4y ago
  https://en.wikipedia.org//wiki/Aerographene https://en.wikipedia.org//wiki/Aerographene It is approximately 7.5 times less dense than air. Note that the cited density does not include the weight of the air incorporated in the structure: it does not float in air.

idiotsecant 4y ago

Seems like some of the bad parts of terrestrial solar (fighting atmospheric conditions, wind loading, etc) without the good parts of orbital solar (once you're in orbit, staying there is relatively easy and you have very little in the way of mechanical stresses for your solar array, so you can make it really huge). I might not be thinking about it hard enough.

LarryMullins 4y ago

> 5k-6k meter altitude That's not high enough to put you above bad weather (airliners fly higher, and they divert around storms.) Bad weather is bad news for airships and historically destroyed about as many as hydrogen fires. You'd need to bring your airships down into hangers when the weather got bad. Also, wouldn't the graphene aerogel be filled with air and be heavier than air? Aerogel doesn't just float away. Unless you mean for these to be vacuum airships, but those seem very far fetched.

cwkoss 4y ago
I don't know if a lighter than air brick of aerogel has ever been manufactured. Would helium in the crevices generate enough lift to make a neutrally or negatively buoyant solid? If so, I want one.
- thehappypm 4y ago
  You can get one today, it’s called a balloon
- AlotOfReading 4y ago
  Helium and hydrogen would immediately leak out of an aerogel.
im3w1l 4y ago
> Vacuum airship Wow what a fascinating idea! Just thinking out loud here, but the compressive force is proprtional to area, while the boyancy is proportional to volume. So I wonder if making it big enough would allow using some fairly standard materials. What about a cube made of 6 big (huge) sheets of some strong yet light material supported by a sort of skeleton inside? Or maybe we can use electro-static repulsion to keep it from imploding? Like how a normal balloon compresses the air inside because the rubber tries to shrink but if you had a balloon that tried to expand instead, because of say electric repulsion, or maybe something else, then it would put the air inside at lower than atmospheric pressure.
- dvdkhlng 4y ago
  Last time I read about that, the problem seemed to be buckling [1]. E.g. if you look at Euler's critical load [2] then the pressure that a slender column can withstand just depends on the aspect ratio of the column (imagine a vacuum airship that uses internal columns to withstand the air pressure). So scaling things up means, that the column's weight has to scale proportionally with total airship volume (and the (air) pressure is a constant anyways). See also these discussions here [3]. Disclaimer: I don't claim to understand any of this. [1] https://en.wikipedia.org/wiki/Buckling https://en.wikipedia.org/wiki/Buckling [2] https://en.wikipedia.org/wiki/Euler%27s_critical_load https://en.wikipedia.org/wiki/Euler%27s_critical_load [3] https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship

DennisP 4y ago

Biggest advantage of solar in geostationary is that you get power 24/7, so you don't need a lot of storage. You're not in shadow at all except for a little bit around the equinoxes. Total uptime is 99.5%.

tzs 4y ago

There have been proposals to use things at that kind of altitude for power, but the ones I've seen have been for wind power rather than solar power. The idea is to have something that is tethered to the ground and held aloft by the winds at high altitude and that has wind turbines to generate power, which is sent back to the ground by cable. There are pretty much always strong winds over much of the US at 5k-6k meters, so such a wind power generator would provide 24 hour a day power most of the time. Here's a site showing the wind over the at around the height [1]. Click where it says "earth" in the lower left to change the height. The height is given in pressure. My link is for 500 hPa pressure which is somewhere around 5500 m. The 700 hPa option would be around 3000 m, and the 250 hPa option would be around 9000 m. Here's a site with a graph of pressure vs height if you want to know the heights for the other pressure options [2]. That graph uses kPa. 0.1 kPa = 1 hPa. The proposals I've seen I've proposed a few different things to fly. One is basically just a kite carrying turbines. Another is a parasail. Another is some sort of rotor aircraft similar to a quad drone. I believe I've also seen some that use fixed wing aircraft with propellors. The ones with the rotors or propellers would have electric motors powered from the ground that can be used to get the thing up to operating altitude, and then they switch the motors from taking electricity to drive the rotors/props to letting the wind drive the rotors/props to generate electricity. [1] https://earth.nullschool.net/#current/wind/isobaric/500hPa/orthographic=-101.50,37.23,1306/loc=-98.760,41.176 https://earth.nullschool.net/#current/wind/isobaric/500hPa/o... [2] https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html https://www.engineeringtoolbox.com/air-altitude-pressure-d_4...

chrisdalke 4y ago
Makani (Acquired by Google and shut down) built large airplane/kites which transmitted wind power to the ground via a tether. The engineering challenges were... intense. This was all documented extensively and this documentary summarizes all the footage they took: https://www.youtube.com/watch?v=qd_hEja6bzE https://www.youtube.com/watch?v=qd_hEja6bzE One of my favorite engineering projects and documentaries, just because of the sheer ambition and scale, and the grit of the team to keep pushing through repeated failures. Sad the project was cancelled but it makes sense given the cost and complexity.
chriswarbo 4y ago

interroboink 4y ago

You made me smirk with the combination of "I'm super ignorant on physics" and "I'm quite sure that there would be a viable way to engineer an airship in such a way" (:

zackees 4y ago

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