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Re:Caltech to Launch Space Solar Power Technology Demo into ... by tzs on Thursday January 05, 2023 @07:56PM (#34269464)
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/o...

[2] https://www.engineeringtoolbox.com/air-altitude-pressure-d_4...

Re:Caltech to Launch Space Solar Power Technology Demo into ... by chrisdalke on Thursday January 05, 2023 @09:25PM (#34270173)
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

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.

Re:Caltech to Launch Space Solar Power Technology Demo into ... by chriswarbo on Friday January 06, 2023 @07:18AM (#34273875)
There are also designs which keep the generators on the ground, and turn it by spooling/unspooling the tether e.g. https://en.wikipedia.org/wiki/SkySails