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It's the dawn of the true space age. And though Musk isn't a fan, this could even make solar power satellites economical. The monolithic designs from the 1970s

It's the dawn of the true space age. And though Musk isn't a fan, this could even make solar power satellites economical. The monolithic designs from the 1970s would be absurdly expensive, but modern designs like SPS-Alpha get economies of scale by using lots of small identical parts that self-assemble in orbit. According to the book The Case for Space Solar Power, a 2GW satellite would deliver electricity at 15 cents/kWh at pre-SpaceX launch costs. I plugged BFR's $50/kg into its cost breakdown and got 4 cents/kWh, which is pretty good for zero-carbon baseload. Ground solar is cheaper by itself, but probably not after including storage. The basic idea is geosynchronous orbit, microwave power transmission with a phased array device that requires a reference signal from the target location, and a wire mesh collector several miles wide. Over 24 hours, a solar panel in geosynch collects 5.4 times as much light as one on Earth. At the time the book was written, the power transmission had been tested over a couple dozen miles, and was 40% efficient. Longer-term, if we collect fuel from the moon to go from LEO to GEO, we could make it even cheaper.

newguynewguy 7y ago
Aren't there some pretty serious health and ecological problems with such large-scale microwave transmission?
- vardump 7y ago
  Perhaps, but several orders of magnitude less bad than health and ecological problems from sunlight.
  - test6554 7y ago
    How can you get more power from an orders of magnitude less powerful beam than from an orders of magnitude more powerful beam (sunlight) over an equal surface area? And if you can’t, why do it? This blows my mind.
    - MayeulC 7y ago
      Disclaimer: I do not know the specifics, but I guess neither do you. The gist of it is probably that more energy gets transmitted per surface unit, but in a way that's less dangerous than sunlight. Firstly, you have 24/365 production, always at peak power. All things equal, you need a lot less capacity for equivalent power generation. Then, I am fairly certain that the amount of power that can be collected depends a lot on antenna size, just like standard wireless transmission: the antenna needs to be "tuned". And a few hundred meters of steel cable would likely absorb a lot more energy than an 80 L water bag. And finally (but related), microwaves are likely a lot less dangerous than UV: it isn't ionizing, because individual photons cary a lot less energy. That also means that they penetrate more "cooking" (increasing temperature) more deeply the objects in its path. Instead of getting your skin burnt from the energy, you feel slightly warmed up (and would likely be able to dissipate the small extra heat in the atmosphere). A sizeable portion of this energy would likely end up in the ground, if no antenna is present to collect it. This technology is interesting, as it offers a lot of new possibilities: it's easy to relocate, for instance. We might also be able to split the beam to power multiple places simultaneously, reducing grid losses (and load balancing at the satellite).
- DennisP 7y ago
  Not really. Even at the intended target, it's diffuse enough not to raise body temperature much. Birds could fly through without harm. Under the antenna, there'd be very little microwaves leaking through. Aim anywhere without a homing signal and you lose the coherent beam, making it much more diffuse.
  - Rediscover 7y ago
    iirc, Novar Conrols/Novar Electronics out of Barberton Ohio (at the time) was testing the phased arrays using bees and their hives and what ever else got in the area. Oh, yeah, and apparently some of the engineers and the boss. (I used to work in a lab there next to some of the equipment and one day I asked my good friend about it - he had been there for decades.)
ben_w 7y ago
Geostationary orbit is further away than the most distant part of the Earth. If you have a way to transmit power efficiently over that distance, it’s still going to be cheaper to put the panels on the ground in Nevada, the Sahara, Saudi Arabia, the Gobi, and Australia, and transmit the power from there. (Microwave towers, LEO satellite relays, superconducting wire, whatever). It’s likely to be really hard to make it efficient to transmit the power, because either it will be microwaves or it will be lasers; lasers can be blocked by clouds, microwaves need an huge antenna at each end (the numbers I’ve seen say that the one on the ground has to be big enough that people will ask why you’re not just using building a PV solar array on the ground instead of the antenna). If the antenna isn’t big enough, transmission losses from beamed power is proportional to distance squared, whereas resistance loss in wires is only proportional to distance (P = I²R, R = distance * some_design_specific_number Ω/m). And that’s without the geopolitical implications of anyone worrying if the enormous directed microwave/laser source could be weaponised. Just saying “trust us” isn’t going to be good enough.
- DennisP 7y ago
  Why not PV on the ground: because wire antenna is a lot cheaper. Why people don't have to trust us: because the technology isn't physically capable of maintaining even that low energy density at the target, without the reference signal from the ground. Why put the PV in space instead of on the ground: because there's 5.4X as much energy available and it's 24/7. There's real engineering behind this design, detailed in the book and the SPS-Alpha final report to NASA: https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alpha.pdf https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alp... I'm not aware of any real engineering studies for things like transmitting power via LEO satellite relays from the Sahara. Personally I don't find it plausible, but if you can provide such a study I'm willing to change my mind.
  - ben_w 7y ago
    > Why people don't have to trust us: because the technology isn't physically capable of maintaining even that low energy density at the target, without the reference signal from the ground. From what I see that’s a design choice not a fundamental aspect of reality, but even if it isn’t: what stops a hostile actor creating their own guide signal, either to direct the power towards an vulnerable location, or to directed away from the receiver, causing wide-scale power outages in the process? > I'm not aware of any real engineering studies for things like transmitting power via LEO satellite relays from the Sahara. Personally I don't find it plausible, but if you can provide such a study I'm willing to change my mind. This is because beamed power in general is a bad idea compared to simple wires, however the Sahara is a lot closer than Geostationary orbit and therefore any technology that works for Geostationary orbit will also work for the Sahara, and at guaranteed lower cost regardless of the technology.

newguynewguy 7y ago

Aren't there some pretty serious health and ecological problems with such large-scale microwave transmission?

vardump 7y ago
Perhaps, but several orders of magnitude less bad than health and ecological problems from sunlight.
- test6554 7y ago
  How can you get more power from an orders of magnitude less powerful beam than from an orders of magnitude more powerful beam (sunlight) over an equal surface area? And if you can’t, why do it? This blows my mind.
  - MayeulC 7y ago
    Disclaimer: I do not know the specifics, but I guess neither do you. The gist of it is probably that more energy gets transmitted per surface unit, but in a way that's less dangerous than sunlight. Firstly, you have 24/365 production, always at peak power. All things equal, you need a lot less capacity for equivalent power generation. Then, I am fairly certain that the amount of power that can be collected depends a lot on antenna size, just like standard wireless transmission: the antenna needs to be "tuned". And a few hundred meters of steel cable would likely absorb a lot more energy than an 80 L water bag. And finally (but related), microwaves are likely a lot less dangerous than UV: it isn't ionizing, because individual photons cary a lot less energy. That also means that they penetrate more "cooking" (increasing temperature) more deeply the objects in its path. Instead of getting your skin burnt from the energy, you feel slightly warmed up (and would likely be able to dissipate the small extra heat in the atmosphere). A sizeable portion of this energy would likely end up in the ground, if no antenna is present to collect it. This technology is interesting, as it offers a lot of new possibilities: it's easy to relocate, for instance. We might also be able to split the beam to power multiple places simultaneously, reducing grid losses (and load balancing at the satellite).
DennisP 7y ago
Not really. Even at the intended target, it's diffuse enough not to raise body temperature much. Birds could fly through without harm. Under the antenna, there'd be very little microwaves leaking through. Aim anywhere without a homing signal and you lose the coherent beam, making it much more diffuse.
- Rediscover 7y ago
  iirc, Novar Conrols/Novar Electronics out of Barberton Ohio (at the time) was testing the phased arrays using bees and their hives and what ever else got in the area. Oh, yeah, and apparently some of the engineers and the boss. (I used to work in a lab there next to some of the equipment and one day I asked my good friend about it - he had been there for decades.)

ben_w 7y ago

Geostationary orbit is further away than the most distant part of the Earth. If you have a way to transmit power efficiently over that distance, it’s still going to be cheaper to put the panels on the ground in Nevada, the Sahara, Saudi Arabia, the Gobi, and Australia, and transmit the power from there. (Microwave towers, LEO satellite relays, superconducting wire, whatever). It’s likely to be really hard to make it efficient to transmit the power, because either it will be microwaves or it will be lasers; lasers can be blocked by clouds, microwaves need an huge antenna at each end (the numbers I’ve seen say that the one on the ground has to be big enough that people will ask why you’re not just using building a PV solar array on the ground instead of the antenna). If the antenna isn’t big enough, transmission losses from beamed power is proportional to distance squared, whereas resistance loss in wires is only proportional to distance (P = I²R, R = distance * some_design_specific_number Ω/m). And that’s without the geopolitical implications of anyone worrying if the enormous directed microwave/laser source could be weaponised. Just saying “trust us” isn’t going to be good enough.

DennisP 7y ago
Why not PV on the ground: because wire antenna is a lot cheaper. Why people don't have to trust us: because the technology isn't physically capable of maintaining even that low energy density at the target, without the reference signal from the ground. Why put the PV in space instead of on the ground: because there's 5.4X as much energy available and it's 24/7. There's real engineering behind this design, detailed in the book and the SPS-Alpha final report to NASA: https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alpha.pdf https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_Alp... I'm not aware of any real engineering studies for things like transmitting power via LEO satellite relays from the Sahara. Personally I don't find it plausible, but if you can provide such a study I'm willing to change my mind.
- ben_w 7y ago
  > Why people don't have to trust us: because the technology isn't physically capable of maintaining even that low energy density at the target, without the reference signal from the ground. From what I see that’s a design choice not a fundamental aspect of reality, but even if it isn’t: what stops a hostile actor creating their own guide signal, either to direct the power towards an vulnerable location, or to directed away from the receiver, causing wide-scale power outages in the process? > I'm not aware of any real engineering studies for things like transmitting power via LEO satellite relays from the Sahara. Personally I don't find it plausible, but if you can provide such a study I'm willing to change my mind. This is because beamed power in general is a bad idea compared to simple wires, however the Sahara is a lot closer than Geostationary orbit and therefore any technology that works for Geostationary orbit will also work for the Sahara, and at guaranteed lower cost regardless of the technology.