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China wants to put a solar farm in space by 2025

engadget.com

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Re: China wants to put a solar farm in space by 2025

#51

Post by JoeAltmaier »

dexen wrote: post #25

A doomsday weapon in space. As the article mentions, the station will beam the collected energy down to Earth. Whether in visible light, microwave or any other spectral band, it will need two things for everyday operations: - ability to point the beam at an arbitrary point on Earth, to track the collector ground installation, and - ability to focus the beam to proper size The second capability is crucial; if it's fix…

It'll be the largest most fragile thing in the sky - kilometers wide and trivially destabilized/neutralized. Think black paint.

We seem to be arguing It'll be terribly expensive and difficult to make work, on one hand, and It'll be trivially easy to make into a weapon, on the other.

Re: China wants to put a solar farm in space by 2025

#52

Post by adrianN »

AstralStorm wrote: post #50
adrianN wrote: post #41

Earlier quoted context omitted.

Solar panels in space also work during the night and while it's cloudy. Did your calculation include the energy costs of storage?

You do know that one can build the panels on the other hemisphere, right? It is all a small matter of building a long enough high voltage DC line. Mostly a political problem. Or you can use microwaves on ground if it is easier to build a bunch of antennas. Ultimately also reflect off space mirrors (meshes) for much cheaper. The main problem is theoretically weather. Space has the other kind of weather called space ju…

HVDC lines are really neat tech and I fully support solar farms in the Sahara to supply Europe, but I wouldn't be surprised if it's cheaper to launch satellites than to build a global power grid that can provide solar power over night.

I think debris is not a terrible problem right now. We manage to have a large number of satellites in high orbits.

Re: China wants to put a solar farm in space by 2025

#53

Post by AstralStorm »

DennisP wrote: post #47
AstralStorm wrote: post #43

Earlier quoted context omitted.

It would be competitive, if there were no nuclear power or maintenance costs or manufacturing costs. These are not counted in launch costs. You have to launch replacement panels pretty often due to trash collisions or put them in a less than convenient orbit. The space solar module with a good enough battery and emitter would cost about as much as half a radiotelescope... Because it is one. And consider we have probl…

The costs I quoted include everything, including manufacturing and maintenance. The book breaks down all these costs. In the 4 cents/kWh scenario, launch isn't the dominant cost anymore, and dropping that further wouldn't make much difference. You don't put a battery on a solar power satellite. To whatever extent you need battery, you put it on the ground, but you don't need much because a satellite in geosynchronous…

You want to put it in synchronous? How do you keep it lit up all the time?

You do understand you need many more panel fields as opposed to receiving stations that way and half of them is wasted anyway?

I thought the idea is to put them in solar Lagrange or solar synchronous orbit and bend or reflect the maser to stations. 24 hour lit, though a bit trashy if Lsun is used.

The math is suspicious anyway. Wouldn't it mean that the panels would cost 25% of this on ground?

Re: China wants to put a solar farm in space by 2025

#54

Post by AstralStorm »

JoeAltmaier wrote: post #51
dexen wrote: post #25

A doomsday weapon in space. As the article mentions, the station will beam the collected energy down to Earth. Whether in visible light, microwave or any other spectral band, it will need two things for everyday operations: - ability to point the beam at an arbitrary point on Earth, to track the collector ground installation, and - ability to focus the beam to proper size The second capability is crucial; if it's fix…

It'll be the largest most fragile thing in the sky - kilometers wide and trivially destabilized/neutralized. Think black paint. We seem to be arguing It'll be terribly expensive and difficult to make work, on one hand, and It'll be trivially easy to make into a weapon, on the other.

Relatively easy to make work and quite uneconomical compared to ground solar fields. (Multiple.)

Re: China wants to put a solar farm in space by 2025

#55

Post by DennisP »

AstralStorm wrote: post #53
DennisP wrote: post #47

Earlier quoted context omitted.

The costs I quoted include everything, including manufacturing and maintenance. The book breaks down all these costs. In the 4 cents/kWh scenario, launch isn't the dominant cost anymore, and dropping that further wouldn't make much difference. You don't put a battery on a solar power satellite. To whatever extent you need battery, you put it on the ground, but you don't need much because a satellite in geosynchronous…

You want to put it in synchronous? How do you keep it lit up all the time? You do understand you need many more panel fields as opposed to receiving stations that way and half of them is wasted anyway? I thought the idea is to put them in solar Lagrange or solar synchronous orbit and bend or reflect the maser to stations. 24 hour lit, though a bit trashy if Lsun is used. The math is suspicious anyway. Wouldn't it mea…

Due to axial tilt, for most of the year geosynchronous satellites are in full sunlight 24/7. Twice a year, around each equinox, there's a period of 44 days during which the satellite goes into shadow briefly each day, for a time ranging from 2 minutes, to 72 minutes at the maximum.

https://corpblog.viasat.com/how-satellites-are-affected-by-t...

This compares pretty favorably to capacity factors of other power sources.

Illumination per square meter averages quite a bit higher than ground solar, and except for the brief times in shadow is 30% higher than ground solar at noon.

The book evaluated other locations including Lagrange points. Everything had pros and cons; the main disadvantage of Lagrange points was the greater distance, requiring bigger antennas. I think more delta-v in deployment was a factor too, though I forget by how much.

Re: China wants to put a solar farm in space by 2025

#56

Post by adrianN »

ovi256 wrote: post #6
44Aman wrote: post #3

How do they plan to beam energy back to Earth?

They'll recharge batteries that they'll then return to earth on a cheap BFR-like reusable launcher. /joke Internet points to anyone who computes: - how expensive that makes the marginal kWh returned to earth likes this. - how low launch and return-to-earth costs must go for this to become competitive with current kWh costs.

First you build a space elevator to geosynchronous orbit, then you can use full batteries as counterweight for lifting empty batteries. That way you only have to overcome friction losses.

Re: China wants to put a solar farm in space by 2025

#58

Post by DennisP »

dexen wrote: post #25

A doomsday weapon in space. As the article mentions, the station will beam the collected energy down to Earth. Whether in visible light, microwave or any other spectral band, it will need two things for everyday operations: - ability to point the beam at an arbitrary point on Earth, to track the collector ground installation, and - ability to focus the beam to proper size The second capability is crucial; if it's fix…

Based on a book I read on the subject, there's a way to make a phase-array microwave transmitter, which achieves the required focus by tuning into a reference signal from the receiving station on Earth. Using this system, if you try to transmit to an arbitrary spot you'll have a much more diffuse beam, and even the tight beam is only concentrated enough to raise the temperature several degrees. The receiving station is about the size of a ground-based solar array, but cheaper because it's just microwave antenna.

Another approach is to use a laser, at a frequency that gets absorbed by the atmosphere. Beam it to a high-altitude receiver station, which beams microwaves to a receiver directly below. But that way is a lot more expensive.

https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...

Re: China wants to put a solar farm in space by 2025

#59

Post by ovi256 »

adrianN wrote: post #56
ovi256 wrote: post #6

Earlier quoted context omitted.

They'll recharge batteries that they'll then return to earth on a cheap BFR-like reusable launcher. /joke Internet points to anyone who computes: - how expensive that makes the marginal kWh returned to earth likes this. - how low launch and return-to-earth costs must go for this to become competitive with current kWh costs.

First you build a space elevator to geosynchronous orbit, then you can use full batteries as counterweight for lifting empty batteries. That way you only have to overcome friction losses.

Even better! Now it's less of a joke idea. You still have a small shuttle transfer from geosync orbit to wherever the solar farm is (heliosync or a lagrange point to avoid earth shadow), but the delta-v for that is tiny.

However space elevators are still soft SF (still missing a material with enough tensile strength), whereas BFR cheap reusable launchers are hard SF, achievable with current known tech.

Re: China wants to put a solar farm in space by 2025

#60

Post by JoeAltmaier »

AstralStorm wrote: post #54
JoeAltmaier wrote: post #51

Earlier quoted context omitted.

It'll be the largest most fragile thing in the sky - kilometers wide and trivially destabilized/neutralized. Think black paint. We seem to be arguing It'll be terribly expensive and difficult to make work, on one hand, and It'll be trivially easy to make into a weapon, on the other.

Relatively easy to make work and quite uneconomical compared to ground solar fields. (Multiple.)

But indefinitely expandable - up to millions of square kilometers. Try that next to a big city!
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