The detail that has stuck in my mind since the last time I read about this is:
Thermodynamically speaking, if you transmit electricity from outside the Earth onto the Earth – even if you do it perfectly efficiently – you are, by definition, heating the planet.
Based on that I concluded that it is superior to generate electricity with inputs that are already hitting the Earth… But I’d be very interested to learn more about this.
The same thing happens when we create heat on earth with nuclear energy, when >50% is directly used to heat the earth via waste heat, and the electrical part becomes >99% waste heat (some tiny fraction of energy is probably permanently converted to chemical bonds, etc.)
However, this is completely dwarfed by the dynamics of flux in and out of the earth. I forget the exact order of magnitude but I think it's around 100TW, and of course about that amount needs to be rejected to space. The key dynamics that provide us balance are of course the exact and precise quantities of greenhouse gases in the atmosphere, albedo, etc.
And of course, coal and natural gas are releasing stored heat energy too, but their contributions to changes in the atmosphere far exceed the contribution from direct heat energy on the surface of the earth.
This is false, if your SBSP conversion efficiency on the ground is better than solar panels on the ground then you will add less energy to earth by collecting the power in space and transmitting it to the ground then by changing the reflective albedo of desert to a very nonreflective material like solar panels.
You could put the solar panels between the sun and Earth so they only capture photon that would have otherwise hit Earth, if that really matters. This would even be nice because if we wanted to cool the planet down we could just redirect some rays.
But I think using an appreciable amount of the power provided to Earth by the sun is still sci-fi stuff anyway, so we probably can’t make an appreciable dent either way.
Sagan put us at around Kardashev .7, it is a log scale shifted by a constant, apparently we’re under .2%, of what hits the Earth, I guess.
Not all that energy will end as heat. And the surface that it may cover won't be significant compared with the Earth one. And if it is, it may shadow enough surface to actually cool down Earth.
In any case, it won't be worse than releasing a good amount of the captured solar energy in chemical form for millions of years in around a century.
I think the more important facet is the output stage. Almost all energy consumed gets converted to heat, with only a small portion doing usable work. Unless there's a massive improvement in the electrical foundations of compute, we will be producing large amounts of heat no matter where the energy is sourced from.
You also affect how much energy (heat) you radiate from earth's surface into space, by choosing the right color, materials of buildings or land around you.
Ultimately the problem with these plans is that solar panels are cheap, but launching them into space is not. There is no point in the near future where launch costs become so cheap that it doesn't make sense to do this instead just building ten times as many panels for the same cost and installing them around the world. The math may change if we ever deploy a space elevator or do asteroid capture and orbital mining/manufacturing, but those are all in the distant future.
If SpaceX succeeds with Starship, projected launch costs to LEO could be as little as $10/kg. Even off by an order of magnitude, $100s/kg might be enough to make it viable. There are plenty of population centers where land is scarce or there are bureaucratic hurdles due to stubborn land owners.
I haven't followed developments in solar cells or power transmission closely,
but I get the sense that there's only been minor, incremental, improvements.
The math still doesn't work.
I've always wondered (especially after a Dr Hossenfelder video about it). Even if we figured out all of the tech to get such a solar cell satellite into orbit for a reasonable cost, they still need a giant ground station to accept the power. How much power would that ground station generate if it was simply a bunch of solar cells instead of microwave receiver? A space cell might get power 24/7, but if 75% is lost in the conversion, how is that better than a ground based cell that gets power for only 6 hours a day?
Putting cells over the area: You get intermittent power. Putting antennas over the area: You get continuous power. And that's the achillies heel of solar--you can't have things shutting down every time a cloud comes over.
Furthermore, microwave antennas are mesh, not solid. You won't have full sun under it, but neither will it be dark.
That being said, there's a fundamental issue here that without huge improvements in launch costs it's simply not viable unless made out of lunar materials.
And note that it doesn't have to be in a synchronous orbit so long as you permit some movement of the antennas. Put say 25 stations out there and 24 ground stations--they keep hopping to the next station as the Earth rotates underneath, the 25th station is offline because it's in shadow.
Secondary usage as an impromptu death ray is the only way that pencils out for me. Even if you could cut the receiving area to 1/10 the equivalent solar panel area, the economics of launching a huge space array seem really difficult to ever make economic sense vs fully land based system.
This idea made more sense before batteries started to get good. But solar + batteries can get you through the night now.
A panel in space can capture maybe 3x as much energy as one on the ground over a 24 hour cycle. But there are losses in transmission and huge costs to get the thing into space.
> But solar + batteries can get you through the night now.
They can't get you through a month of Dunkelflaute in Germany (that's a 1-in-100 years event), when the normal renewable energy generation is less than 10% of the nameplate capacity.
<antennas so big that we cannot even simulate their behavior.>
I really would love another sentence or two on this. I can't immediately think why that would be, e.g. don't Maxwell's equations apply at very large scales? Any ideas?
"Each megasat could then convert gigawatts of power into a microwave beam aimed precisely at a big field of receiving antennas on Earth. These rectennas would then convert the signal to usable DC electricity."
What are the consequences if, for some reason, the aim becomes not-so-precise?
Vague recollection from studying this years ago...
The "receiver" is more-or-less a field "covered" by a spiderweb of bent coat-hanger wire. That doesn't block the sun, and making it huge (low power/sq. m) is quite cheap.
Since you don't want clouds/rain/fog to block the microwaves, the frequencies you use are ones which water does not absorb well. So if the beam hits a person...he probably can't even notice it.
I guess SimCity 2000 guaranteed this is the first thing everybody thinks about.
It seems that practicality and efficiency concerns limit the beam at between 10% to 30% of the solar intensity. Every single design falls in that range.
The beam is controlled by a signal beamed from the rectenna, which controls the phase of the emitters at the satellite. If this fails, the emitters go out of phase and no beam is formed.
Unfortunately, most of these impossible proposals lack any form of passive failsafe. Plus, the insurance liability question maybe an unsurmountable unknown.
most of these proposals are downright ridiculous because they're couched in environmentalism but they act like nature will be totally fine to have a giant microwave laser or an artificial second moon.
It seems like it could be safer/easier to charge batteries in space and ship them back down... which probably speaks to the feasibility of ideas like this.
Only one measly paragraph on the obvious improvement, eliminating the microwaves. Instead, launch independent steerable mirror satellites of the most economically efficient size, and point them at the highest bidder.
No heavy transmitters or PV cells. No new ground-based infrastructure that has to be built before you can do anything useful.
We don't have the tech to send astronauts to work on a geostationary or geosynchronous satellites. Its a high earth orbit (22,000 miles) and all our tech is for low earth orbit (shuttle, ISS, 400-800 miles) where the ship and station are protected by earth's electromagnetic field and the propellant requirements are much less ... To the best of my knowledge we have never repaired a geosynchronous or geostationary satellite..
You can get into the weeds of the detailed costings, safety, etc, but I think the clearest argument is this:
> The problem with beaming power using microwaves is that the monetizable value per Watt is incredibly low, because essentially unmetered electricity comes out of the walls of every building. The trick is to increase the value per Watt, by increasing the value and decreasing the power. The value is increased by modulating the microwaves with high speed data, and the power can be reduced by a factor of a million or so without hurting this method. Indeed, customers pay only for the data, and not for the transmitted electrical power, which is pathetically low at the receiver. Communications satellites remain the killer app for the commercial space industry
And then you look at the fact that almost every satellite communications company has gone bankrupt at some point. SpaceX with Starlink being a notable exception, but OneWeb which superficially looks pretty similar has already gone bankrupt once. If communications, which is many more orders of magnitude more valuable than power, is not enough to stave off bankruptcy, then there is no possibility of beamed power being economical without a commensurate improvement in the efficiency of space launch. And that's just a baseline as a necessary condition, not actually a sufficient condition for it to be a sensible business.
In general, the energy retention model for earth only keeps less than around 3% of the suns energy hitting our atmosphere. Shifting this property even by a fraction of a percent causes cascade shifts in global climate and ecology.
"There is always a well-known solution to every human problem - neat, plausible and wrong" (Mencken, 1920)
Threat assessment: what if a given technology is wielded by an insane king? ...because all things are eventually... =3
The main issue with beaming solar power from orbit to surface is that this can be a weapon at a push of a button. There is no way you can make the owner of that orbit-based power station to promise they'll never redirect the beam, under any circumstances, cross their heart and hope to die. The only way to not have that threat is to not have the power station up there.
And that's how it's going to be. No matter how technically feasible the idea will ever be, it will never materialize, because the weaponization potential cannot be eliminated.
There is another problem to solve, which is cooling the Earth. What does it take to shield the Earth from Sun so less solar power reaches the Earth? Is there such technology?
You could, but the minimum length of a space elevator is 35,786 km and the maximum distance between two points on the surface of the Earth is about 20,000 km, so you might as well just build a surface power grid: your winter solstice midnight is someone else's midday summer solstice, and no dunkelflaute is worldwide.
Much easier on the ground, too, because you don't need to invent even one single new tech — not even better superconductors because even aluminium will work if you make the "wire" thick enough (scare quotes because, by coincidence, the circumference of the earth, 40,000 km, almost perfectly matches the conductivity of aluminium, 3.8e7 S/m, and you get a 1 Ω line from a 1 square meter cross section, which is a pretty thick "wire").
Plus, once it gets down from a space elevator, you then have to distribute it around the ground anyway.
[+] [-] rsync|1 year ago|reply
Thermodynamically speaking, if you transmit electricity from outside the Earth onto the Earth – even if you do it perfectly efficiently – you are, by definition, heating the planet.
Based on that I concluded that it is superior to generate electricity with inputs that are already hitting the Earth… But I’d be very interested to learn more about this.
[+] [-] epistasis|1 year ago|reply
However, this is completely dwarfed by the dynamics of flux in and out of the earth. I forget the exact order of magnitude but I think it's around 100TW, and of course about that amount needs to be rejected to space. The key dynamics that provide us balance are of course the exact and precise quantities of greenhouse gases in the atmosphere, albedo, etc.
And of course, coal and natural gas are releasing stored heat energy too, but their contributions to changes in the atmosphere far exceed the contribution from direct heat energy on the surface of the earth.
[+] [-] tectonic|1 year ago|reply
[+] [-] bee_rider|1 year ago|reply
But I think using an appreciable amount of the power provided to Earth by the sun is still sci-fi stuff anyway, so we probably can’t make an appreciable dent either way.
Sagan put us at around Kardashev .7, it is a log scale shifted by a constant, apparently we’re under .2%, of what hits the Earth, I guess.
https://en.m.wikipedia.org/wiki/Kardashev_scale
[+] [-] IshKebab|1 year ago|reply
You need to get a better handle on orders of magnitude.
[+] [-] kadoban|1 year ago|reply
[+] [-] gmuslera|1 year ago|reply
In any case, it won't be worse than releasing a good amount of the captured solar energy in chemical form for millions of years in around a century.
[+] [-] thelastgallon|1 year ago|reply
This will change when we switch to renewables.
[+] [-] glitchc|1 year ago|reply
[+] [-] m463|1 year ago|reply
[+] [-] unknown|1 year ago|reply
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[+] [-] creer|1 year ago|reply
[+] [-] mjhay|1 year ago|reply
[+] [-] unknown|1 year ago|reply
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[+] [-] TheDudeMan|1 year ago|reply
[+] [-] jandrese|1 year ago|reply
[+] [-] spiralk|1 year ago|reply
[+] [-] cratermoon|1 year ago|reply
I haven't followed developments in solar cells or power transmission closely, but I get the sense that there's only been minor, incremental, improvements. The math still doesn't work.
[+] [-] joshmarinacci|1 year ago|reply
[+] [-] LorenPechtel|1 year ago|reply
Furthermore, microwave antennas are mesh, not solid. You won't have full sun under it, but neither will it be dark.
That being said, there's a fundamental issue here that without huge improvements in launch costs it's simply not viable unless made out of lunar materials.
And note that it doesn't have to be in a synchronous orbit so long as you permit some movement of the antennas. Put say 25 stations out there and 24 ground stations--they keep hopping to the next station as the Earth rotates underneath, the 25th station is offline because it's in shadow.
[+] [-] 0cf8612b2e1e|1 year ago|reply
[+] [-] Animats|1 year ago|reply
A panel in space can capture maybe 3x as much energy as one on the ground over a 24 hour cycle. But there are losses in transmission and huge costs to get the thing into space.
[+] [-] cyberax|1 year ago|reply
They can't get you through a month of Dunkelflaute in Germany (that's a 1-in-100 years event), when the normal renewable energy generation is less than 10% of the nameplate capacity.
[+] [-] rco8786|1 year ago|reply
This feels low to me (not an expert at all). So many advantages in space. much longer sun exposure, no atmosphere or weather to deal with, etc?
[+] [-] jjslocum3|1 year ago|reply
I really would love another sentence or two on this. I can't immediately think why that would be, e.g. don't Maxwell's equations apply at very large scales? Any ideas?
[+] [-] dwpdwpdwpdwpdwp|1 year ago|reply
What are the consequences if, for some reason, the aim becomes not-so-precise?
[+] [-] bell-cot|1 year ago|reply
The "receiver" is more-or-less a field "covered" by a spiderweb of bent coat-hanger wire. That doesn't block the sun, and making it huge (low power/sq. m) is quite cheap.
Since you don't want clouds/rain/fog to block the microwaves, the frequencies you use are ones which water does not absorb well. So if the beam hits a person...he probably can't even notice it.
[+] [-] marcosdumay|1 year ago|reply
It seems that practicality and efficiency concerns limit the beam at between 10% to 30% of the solar intensity. Every single design falls in that range.
[+] [-] throw9474|1 year ago|reply
[+] [-] pfdietz|1 year ago|reply
[+] [-] banish-m4|1 year ago|reply
Unfortunately, most of these impossible proposals lack any form of passive failsafe. Plus, the insurance liability question maybe an unsurmountable unknown.
[+] [-] snickerbockers|1 year ago|reply
[+] [-] micromacrofoot|1 year ago|reply
[+] [-] eagerpace|1 year ago|reply
[+] [-] simonblack|1 year ago|reply
[+] [-] Vegemeister|1 year ago|reply
No heavy transmitters or PV cells. No new ground-based infrastructure that has to be built before you can do anything useful.
[+] [-] kazinator|1 year ago|reply
[+] [-] williamDafoe|1 year ago|reply
[+] [-] dkbrk|1 year ago|reply
- Space-based solar power is not a thing: https://caseyhandmer.wordpress.com/2019/08/20/space-based-so...
- No really, space based solar power is not a useful idea, literature review edition: https://caseyhandmer.wordpress.com/2019/09/20/no-really-spac...
You can get into the weeds of the detailed costings, safety, etc, but I think the clearest argument is this:
> The problem with beaming power using microwaves is that the monetizable value per Watt is incredibly low, because essentially unmetered electricity comes out of the walls of every building. The trick is to increase the value per Watt, by increasing the value and decreasing the power. The value is increased by modulating the microwaves with high speed data, and the power can be reduced by a factor of a million or so without hurting this method. Indeed, customers pay only for the data, and not for the transmitted electrical power, which is pathetically low at the receiver. Communications satellites remain the killer app for the commercial space industry
And then you look at the fact that almost every satellite communications company has gone bankrupt at some point. SpaceX with Starlink being a notable exception, but OneWeb which superficially looks pretty similar has already gone bankrupt once. If communications, which is many more orders of magnitude more valuable than power, is not enough to stave off bankruptcy, then there is no possibility of beamed power being economical without a commensurate improvement in the efficiency of space launch. And that's just a baseline as a necessary condition, not actually a sufficient condition for it to be a sensible business.
[+] [-] Joel_Mckay|1 year ago|reply
"There is always a well-known solution to every human problem - neat, plausible and wrong" (Mencken, 1920)
Threat assessment: what if a given technology is wielded by an insane king? ...because all things are eventually... =3
https://www.youtube.com/watch?v=lITBGjNEp08
[+] [-] credit_guy|1 year ago|reply
And that's how it's going to be. No matter how technically feasible the idea will ever be, it will never materialize, because the weaponization potential cannot be eliminated.
[+] [-] lupusreal|1 year ago|reply
[+] [-] nnurmanov|1 year ago|reply
[+] [-] gmuslera|1 year ago|reply
[+] [-] xaellison|1 year ago|reply
[+] [-] HPsquared|1 year ago|reply
[+] [-] ben_w|1 year ago|reply
Much easier on the ground, too, because you don't need to invent even one single new tech — not even better superconductors because even aluminium will work if you make the "wire" thick enough (scare quotes because, by coincidence, the circumference of the earth, 40,000 km, almost perfectly matches the conductivity of aluminium, 3.8e7 S/m, and you get a 1 Ω line from a 1 square meter cross section, which is a pretty thick "wire").
Plus, once it gets down from a space elevator, you then have to distribute it around the ground anyway.
[+] [-] TheDudeMan|1 year ago|reply
[+] [-] brcmthrowaway|1 year ago|reply