4 ms·

You forgot to explain why this is "pretty obviously a terrible idea".

by p1esk 4y ago

thisisbrians 4y ago
Some ideas about what makes it challenging: - A satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions - A satellite constellation in orbit would need many ground stations to transmit power to from space - Weather will get in the way of transmission to the ground, just like it does with ordinary solar - The cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit
- JumpCrisscross 4y ago
  > satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions Balancing this is at least a half an order of magnitude difference in collection efficiency. > Weather will get in the way of transmission to the ground, just like it does with ordinary solar True. But there are extraterrestrial atmospheres where water vapor and ozone aren’t a problem. (I’ve only seen this proposed with microwave.) > cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit This is the killer. That said, this is a long-term research endeavour. If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift.
  - feoren 4y ago
    > half an order of magnitude Completely off-topic, but would "half an order of magnitude" be sqrt(10)? I've just never heard someone refer to a factor of ~3 as "half an order of magnitude".
    - roelschroeven 4y ago
      Sqrt(10) is approximately 3.162278, that's close enough to 3.
    - deleted 4y ago
      [deleted]
    - JumpCrisscross 4y ago
      > just never heard someone refer to a factor of ~3 as "half an order of magnitude" Last time I looked, the estimates ranged from 270% to 50x. Seeing the latter, my brain went into astronomer mode and then I guess just ran with it.
  - LarryMullins 4y ago
    > If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift. The economics of anything on Mars or the Moon amounts to 'try to convince a government to throw tons of money at you.' A technology which only makes sense in that economic context is very limited.
    - JumpCrisscross 4y ago
      > technology which only makes sense in that economic context is very limited If this were a start-up I’d be roundly criticising it. It’s not. It’s a research project. And each of its sub-projects—testing new PVs in space, a novel deployment mechanism, power transmission—has clear value outside a space-based solar context. As a focussing mechanism, SBSP is neat because each problem needing to be solved to make it economically viable is immediately valuable on the ground. (Save for power transmission. That’s still niche.)
      - LarryMullins 4y ago
        > Save for power transmission Isn't that the entire point? Putting solar panels in space has been done regularly the 1950s.
        JumpCrisscross 4y ago
        I meant that I don't see a near-term use terrestrial use case for better microwave power transmission.
        LarryMullins 4y ago
        Maybe you could use microwave power transmission (from the ground) to power atmospheric pseudo-satellites, but practical applications seem dubious.
        ben_w 4y ago
        Drones. Electric aircraft in general, recharging continuously in-flight. Might be ill-advised for a whole mass of reasons that I, as a software engineer, know naught of; but it would be a use case.
  - wrycoder 4y ago
    > cost of getting a PV array into orbit is very expensive Musk will find a way. Another stepping stone to Mars.
    - ben_w 4y ago
      It would be great on Mars. Mars has planet-wide dust storms. But for Earth, even if it was free to put the PV in Earth orbit, the ground stations need to have an incredibly low total cost to make sense. I can't remember how low exactly.
      - DennisP 4y ago
        The ground stations are basically just antenna wire. For a large plant they would contribute just 0.7 cents/kWh to the total cost, according to the book The Case for Space Solar Power.
        ben_w 4y ago
        Also needs a microwave frequency rectifier, plus installation costs are non-trivial as evidenced by the difference between the cost/W of a PV cell and a PV farm. Also, cheapest ground-based PV in the world is 1.04¢/kWh (Saudi Arabia), and the cheapest in the USA is 1.50¢/kWh (New Mexico), so 0.7¢/kWh is already a large percentage. https://commercialsolarguy.com/lowest-solar-power-prices-in-the-world/ https://commercialsolarguy.com/lowest-solar-power-prices-in-...
        DennisP 4y ago
        Just to clarify, the 0.7 cents is total ground station cost, according to my source. At ideal locations, ground solar is super cheap, but the microwave receiver works anywhere. Not needing storage is a big difference, too.
        ben_w 4y ago
        That seems a bit optimistic, but I don't have the book, so OK. (I really should get around to blogging what I think is wrong with this whole approach to space solar, where it works despite that, and how to improve on it for Earth usage; it comes up here every so often, and linking to my blog is easier than disjointed comments without images).
- p1esk 4y ago
  None of these seem like obvious show stoppers.
josh11b 4y ago
https://caseyhandmer.wordpress.com/2019/08/20/space-based-solar-power-is-not-a-thing/ https://caseyhandmer.wordpress.com/2019/08/20/space-based-so...
- deleted 4y ago
  [deleted]
IshKebab 4y ago
Even ignoring the power transmission challenges, putting stuff in orbit is really really expensive. Surely you knew that?
- DennisP 4y ago
  For now. But if SpaceX succeeds in getting launch costs below $50/kg with Starship, space solar starts looking a lot more attractive. Advertised price on Falcon Heavy is already just $600/kg to LEO. A big part of that is the throwaway upper stage, which Starship eliminates.
  - IshKebab 4y ago
    Falcon Heavy is around $2300/kg to LEO. Not sure where you got $600 from. I'm sure Starship will be better, but 40 times cheaper? I doubt it.
    - DennisP 4y ago
      Just checked and the answer splits the difference. $97M for a Heavy launch, divided by 63,800 kg payload to LEO gives $1520/kg. I think my $600 must have been per pound (though that's still a bit off, at the current price). https://www.spacex.com/media/Capabilities&Services.pdf https://www.spacex.com/media/Capabilities&Services.pdf The biggest cost is throwing away hardware. If you're not doing that, you can amortize your entire hardware cost over the number of launches. At Falcon's launch cadence that's still going to be significant. But Starship is designed to do hundreds of launches per year, and if they manage it then hardware cost per launch is almost nothing. Then you're mainly paying for fuel and ground services, which are about a million dollars each. 100 tonnes to LEO for $2M gives just $20/kg, leaving plenty of margin for SpaceX at $50. It might seem hard to envision putting that much cargo into space every year, but if we did solar power satellites at scale, that's exactly what we'd need.
      - IshKebab 4y ago
        > $97M for a Heavy launch, divided by 63,800 kg payload to LEO No, $97M is for a launch with reused boosters. 63,800 kg to LEO is when the boosters are dispended.
cratermoon 4y ago
https://dothemath.ucsd.edu/2012/03/space-based-solar-power/ https://dothemath.ucsd.edu/2012/03/space-based-solar-power/

You forgot to explain why this is "pretty obviously a terrible idea".

by p1esk 4y ago

You forgot to explain why this is "pretty obviously a terrible idea".

Some ideas about what makes it challenging: - A satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions - A satellite constellation in orbit would need many ground stations to transmit power to from space - Weather will get in the way of transmission to the ground, just like it does with ordinary solar - The cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit

JumpCrisscross 4y ago
> satellite will have to transmit power through the entire atmosphere from space, which will have substantial losses even in perfect conditions Balancing this is at least a half an order of magnitude difference in collection efficiency. > Weather will get in the way of transmission to the ground, just like it does with ordinary solar True. But there are extraterrestrial atmospheres where water vapor and ozone aren’t a problem. (I’ve only seen this proposed with microwave.) > cost of getting a PV array into orbit is very expensive relative to the amount of power it can generate and transmit This is the killer. That said, this is a long-term research endeavour. If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift.
- feoren 4y ago
  > half an order of magnitude Completely off-topic, but would "half an order of magnitude" be sqrt(10)? I've just never heard someone refer to a factor of ~3 as "half an order of magnitude".
  - roelschroeven 4y ago
    Sqrt(10) is approximately 3.162278, that's close enough to 3.
  - deleted 4y ago
    [deleted]
  - JumpCrisscross 4y ago
    > just never heard someone refer to a factor of ~3 as "half an order of magnitude" Last time I looked, the estimates ranged from 270% to 50x. Seeing the latter, my brain went into astronomer mode and then I guess just ran with it.
- LarryMullins 4y ago
  > If we contemplate such an array around the Moon or on Mars, or in a world with in-space resource extraction and manufacturing, the economics shift. The economics of anything on Mars or the Moon amounts to 'try to convince a government to throw tons of money at you.' A technology which only makes sense in that economic context is very limited.
  - JumpCrisscross 4y ago
    > technology which only makes sense in that economic context is very limited If this were a start-up I’d be roundly criticising it. It’s not. It’s a research project. And each of its sub-projects—testing new PVs in space, a novel deployment mechanism, power transmission—has clear value outside a space-based solar context. As a focussing mechanism, SBSP is neat because each problem needing to be solved to make it economically viable is immediately valuable on the ground. (Save for power transmission. That’s still niche.)
    - LarryMullins 4y ago
      > Save for power transmission Isn't that the entire point? Putting solar panels in space has been done regularly the 1950s.
      - JumpCrisscross 4y ago
        I meant that I don't see a near-term use terrestrial use case for better microwave power transmission.
        LarryMullins 4y ago
        Maybe you could use microwave power transmission (from the ground) to power atmospheric pseudo-satellites, but practical applications seem dubious.
        ben_w 4y ago
        Drones. Electric aircraft in general, recharging continuously in-flight. Might be ill-advised for a whole mass of reasons that I, as a software engineer, know naught of; but it would be a use case.
- wrycoder 4y ago
  > cost of getting a PV array into orbit is very expensive Musk will find a way. Another stepping stone to Mars.
  - ben_w 4y ago
    It would be great on Mars. Mars has planet-wide dust storms. But for Earth, even if it was free to put the PV in Earth orbit, the ground stations need to have an incredibly low total cost to make sense. I can't remember how low exactly.
    - DennisP 4y ago
      The ground stations are basically just antenna wire. For a large plant they would contribute just 0.7 cents/kWh to the total cost, according to the book The Case for Space Solar Power.
      - ben_w 4y ago
        Also needs a microwave frequency rectifier, plus installation costs are non-trivial as evidenced by the difference between the cost/W of a PV cell and a PV farm. Also, cheapest ground-based PV in the world is 1.04¢/kWh (Saudi Arabia), and the cheapest in the USA is 1.50¢/kWh (New Mexico), so 0.7¢/kWh is already a large percentage. https://commercialsolarguy.com/lowest-solar-power-prices-in-the-world/ https://commercialsolarguy.com/lowest-solar-power-prices-in-...
        DennisP 4y ago
        Just to clarify, the 0.7 cents is total ground station cost, according to my source. At ideal locations, ground solar is super cheap, but the microwave receiver works anywhere. Not needing storage is a big difference, too.
        ben_w 4y ago
        That seems a bit optimistic, but I don't have the book, so OK. (I really should get around to blogging what I think is wrong with this whole approach to space solar, where it works despite that, and how to improve on it for Earth usage; it comes up here every so often, and linking to my blog is easier than disjointed comments without images).
p1esk 4y ago
None of these seem like obvious show stoppers.

josh11b 4y ago

https://caseyhandmer.wordpress.com/2019/08/20/space-based-solar-power-is-not-a-thing/ https://caseyhandmer.wordpress.com/2019/08/20/space-based-so...

deleted 4y ago
[deleted]

IshKebab 4y ago

Even ignoring the power transmission challenges, putting stuff in orbit is really really expensive. Surely you knew that?

DennisP 4y ago
For now. But if SpaceX succeeds in getting launch costs below $50/kg with Starship, space solar starts looking a lot more attractive. Advertised price on Falcon Heavy is already just $600/kg to LEO. A big part of that is the throwaway upper stage, which Starship eliminates.
- IshKebab 4y ago
  Falcon Heavy is around $2300/kg to LEO. Not sure where you got $600 from. I'm sure Starship will be better, but 40 times cheaper? I doubt it.
  - DennisP 4y ago
    Just checked and the answer splits the difference. $97M for a Heavy launch, divided by 63,800 kg payload to LEO gives $1520/kg. I think my $600 must have been per pound (though that's still a bit off, at the current price). https://www.spacex.com/media/Capabilities&Services.pdf https://www.spacex.com/media/Capabilities&Services.pdf The biggest cost is throwing away hardware. If you're not doing that, you can amortize your entire hardware cost over the number of launches. At Falcon's launch cadence that's still going to be significant. But Starship is designed to do hundreds of launches per year, and if they manage it then hardware cost per launch is almost nothing. Then you're mainly paying for fuel and ground services, which are about a million dollars each. 100 tonnes to LEO for $2M gives just $20/kg, leaving plenty of margin for SpaceX at $50. It might seem hard to envision putting that much cargo into space every year, but if we did solar power satellites at scale, that's exactly what we'd need.
    - IshKebab 4y ago
      > $97M for a Heavy launch, divided by 63,800 kg payload to LEO No, $97M is for a launch with reused boosters. 63,800 kg to LEO is when the boosters are dispended.

cratermoon 4y ago

https://dothemath.ucsd.edu/2012/03/space-based-solar-power/ https://dothemath.ucsd.edu/2012/03/space-based-solar-power/