4 ms·

Solar flux outside the atmosphere is not, in fact, 9x sea level. You can cook the numbers by keeping the orbital panel square on to the sun, while the ground-mo

by ncmncm 4y ago

Solar flux outside the atmosphere is not, in fact, 9x sea level. You can cook the numbers by keeping the orbital panel square on to the sun, while the ground-mounted panel rotates through the day and overnight. But you don't get to count nighttime twice. Conversion losses of only 20% from electric to laser, and again from laser to electric again, would be miraculous. 20% scattering loss in clear weather would be unsurprising. 90% loss, total, would be admirable, not counting the original 60%+ loss off the top. So, even with 9x, and neglecting huge launch cost you still come out behind.

JoeAltmaier 4y ago
I looked it up. So about 75% of solar radiation reaches the ground. In the continental US, factoring in angle of the sun, average weather, night that comes to about 4-5KWh per day In orbit you would have just 1.37KW X 24 hours (no weather, angle issues) which comes to about 33KWh per day. So that's 8-9X the collected energy per square meter in orbit vs ground level. These folks https://www.allaboutcircuits.com/news/wireless-power-transmission-of-solar-energy-from-space/ https://www.allaboutcircuits.com/news/wireless-power-transmi... estimate 89% efficiency from orbit to ground. So we're then at around 30KWh effective. What am I missing?
- Schroedingersat 4y ago
  > What am I missing? So many things. The massive clear area around your receiver. Scattering induced by weather means you still don't have 100% capacity factor. With only radiative cooling available, cooling will take up as much space as the panels and make everything heavier. The atmosphere doesn't absorb light uniformly. Maintenance. You're comparing fixed panels at mid latitudes to rotating panels. Launch costs are still 10x the cost of a panel. UV and ionizing radiation will destroy your panels sooner. And a space borne panel will probably never reach net energy payback even before you add your laser boondoggle. You're better off just burning the methane.
  - JoeAltmaier 4y ago
    Multiple Gigawatt. Still orders of magnitude better than solar; still less land area. The land-based panels are 42lbs for 450W. The space-based ones are 6W per gram. Lots of room in the equation for cooling. The 89% transmission already figured in weather and absorption; you don't get to count that twice. Rotating panels get what? 25% better? Still an order of magnitude improvement. Launch costs are dropping like a stone. Plan now; it'll be in the hundreds of dollars when you launch. The slang about 'it'll never pay' is just talk. I'd hoped for some information, not just wet-blanket doubt. Like the hot air about 9X being so far from the truth. Turns out, it's just about right. So I guess I'll have to look elsewhere for more information. Somebody will make an orbital station, use it for space-based operations and all the hot air will disappear. And not that far in the future.
    - Schroedingersat 4y ago
      > Multiple Gigawatt. Still orders of magnitude better than solar; still less land area. Land area is an absolute non issue for solar. With the exception of somewhere like luxembourg, just the roofs of the residential areas of a country have enough area to provide the total primary energy consumption. The singular and overriding factor is cost and cost of storing or moving the energy. Which brings me to > The land-based panels are 42lbs for 450W. The space-based ones are 6W per gram. Lots of room in the equation for cooling. You're not going to get nameplate capacity, and the weight is in the superstructure, cooling system, power delivery, and your 100s of metres aperture laser or maser. The actual panel for a terrestrial caravan system I installed recently weighed no more than the panels listed here https://www.spectrolab.com/DataSheets/Panel/panels.pdf https://www.spectrolab.com/DataSheets/Panel/panels.pdf (although it was bigger). So you're proposing spending 10x as much on panels, another 10x as much on cooling, spending as much again on a transmitter, then as much again on a receiver. All to burn tens of kg of methane per watt in order to get the thing into a stationary orbit. Then you have a gigawatt death beam fucking up the atmosphere and making a square kilometer or so uninhabitable. > Like the hot air about 9X being so far from the truth Comparing like for like, you have about 1.3kW in space vs 1kW on the ground, and a tracking setup can get 6kWh/day out of a 1kW panel at low to moderate latitudes (where well over half of the world's population lives). This is a factor of 5 to 6 better, although your space based panel is vastly more expensive and a tracking system is pointless because cost is the limit, not area. This is the most efficient high power long range wireless transmission system I can see mentioned: https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/iet-map.2017.0530 https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049... which brings the ratio to around 3-4. Except you also have to deal with losses due to clouds and dust so 2-3 is more likely. At that point just build a nuclear plant. They're awful but they're better than this plan by every metric. Or do the sensible sane thing and build 100x the terrestrial solar for the same price (or 10x as much and enough storage) and save the space arrays for stuff in space -- once you're lifting megatons it makes far more sense to refine metals from asteroids and just leave 99% of them up there. Or as I said, just burn the rocket fuel in a gas turbine. You'll get more energy out of it than you would from this utterly ridiculous machine in its lifetime. If area was a constraint important enough to make space based solar viable we'd see water cooled triple junction cells as well as tracking on any utility scale installations near the equator (as this would reduce area by 2/3rds). We don't so it can be safely dismissed as more solar frickin roadways.

by ncmncm 4y ago

JoeAltmaier 4y ago

I looked it up. So about 75% of solar radiation reaches the ground. In the continental US, factoring in angle of the sun, average weather, night that comes to about 4-5KWh per day In orbit you would have just 1.37KW X 24 hours (no weather, angle issues) which comes to about 33KWh per day. So that's 8-9X the collected energy per square meter in orbit vs ground level. These folks https://www.allaboutcircuits.com/news/wireless-power-transmission-of-solar-energy-from-space/ https://www.allaboutcircuits.com/news/wireless-power-transmi... estimate 89% efficiency from orbit to ground. So we're then at around 30KWh effective. What am I missing?

Schroedingersat 4y ago
> What am I missing? So many things. The massive clear area around your receiver. Scattering induced by weather means you still don't have 100% capacity factor. With only radiative cooling available, cooling will take up as much space as the panels and make everything heavier. The atmosphere doesn't absorb light uniformly. Maintenance. You're comparing fixed panels at mid latitudes to rotating panels. Launch costs are still 10x the cost of a panel. UV and ionizing radiation will destroy your panels sooner. And a space borne panel will probably never reach net energy payback even before you add your laser boondoggle. You're better off just burning the methane.
- JoeAltmaier 4y ago
  Multiple Gigawatt. Still orders of magnitude better than solar; still less land area. The land-based panels are 42lbs for 450W. The space-based ones are 6W per gram. Lots of room in the equation for cooling. The 89% transmission already figured in weather and absorption; you don't get to count that twice. Rotating panels get what? 25% better? Still an order of magnitude improvement. Launch costs are dropping like a stone. Plan now; it'll be in the hundreds of dollars when you launch. The slang about 'it'll never pay' is just talk. I'd hoped for some information, not just wet-blanket doubt. Like the hot air about 9X being so far from the truth. Turns out, it's just about right. So I guess I'll have to look elsewhere for more information. Somebody will make an orbital station, use it for space-based operations and all the hot air will disappear. And not that far in the future.
  - Schroedingersat 4y ago
    > Multiple Gigawatt. Still orders of magnitude better than solar; still less land area. Land area is an absolute non issue for solar. With the exception of somewhere like luxembourg, just the roofs of the residential areas of a country have enough area to provide the total primary energy consumption. The singular and overriding factor is cost and cost of storing or moving the energy. Which brings me to > The land-based panels are 42lbs for 450W. The space-based ones are 6W per gram. Lots of room in the equation for cooling. You're not going to get nameplate capacity, and the weight is in the superstructure, cooling system, power delivery, and your 100s of metres aperture laser or maser. The actual panel for a terrestrial caravan system I installed recently weighed no more than the panels listed here https://www.spectrolab.com/DataSheets/Panel/panels.pdf https://www.spectrolab.com/DataSheets/Panel/panels.pdf (although it was bigger). So you're proposing spending 10x as much on panels, another 10x as much on cooling, spending as much again on a transmitter, then as much again on a receiver. All to burn tens of kg of methane per watt in order to get the thing into a stationary orbit. Then you have a gigawatt death beam fucking up the atmosphere and making a square kilometer or so uninhabitable. > Like the hot air about 9X being so far from the truth Comparing like for like, you have about 1.3kW in space vs 1kW on the ground, and a tracking setup can get 6kWh/day out of a 1kW panel at low to moderate latitudes (where well over half of the world's population lives). This is a factor of 5 to 6 better, although your space based panel is vastly more expensive and a tracking system is pointless because cost is the limit, not area. This is the most efficient high power long range wireless transmission system I can see mentioned: https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049/iet-map.2017.0530 https://ietresearch.onlinelibrary.wiley.com/doi/full/10.1049... which brings the ratio to around 3-4. Except you also have to deal with losses due to clouds and dust so 2-3 is more likely. At that point just build a nuclear plant. They're awful but they're better than this plan by every metric. Or do the sensible sane thing and build 100x the terrestrial solar for the same price (or 10x as much and enough storage) and save the space arrays for stuff in space -- once you're lifting megatons it makes far more sense to refine metals from asteroids and just leave 99% of them up there. Or as I said, just burn the rocket fuel in a gas turbine. You'll get more energy out of it than you would from this utterly ridiculous machine in its lifetime. If area was a constraint important enough to make space based solar viable we'd see water cooled triple junction cells as well as tracking on any utility scale installations near the equator (as this would reduce area by 2/3rds). We don't so it can be safely dismissed as more solar frickin roadways.