> The advantage of transmitting power from space instead of the other side of the planet is that there's a straight line with no planet in the way. To go around the planet you need relay stations or wires.

Which is why I said 20,000 km not 12,000 km. Even if the circuit approximates the Earth as a square and goes up 6,000 km, turns 90 degrees at one relay, goes 12,000 km, makes another 90 turn at a second relay, and then 6,000 km down, that’s still a shorter path (though I’d expect the important distance in that instance to be 12,000 km not 24,000 km because it’s related to the inverse square law between any two antennas not over the whole distance).

> Maybe even take a quick look at the NASA report I provided, too.

I did. Now that I no longer at work I have time for a more detailed (though still brief) look at the contents rather than just skim read.

• That research was an attempt to turn a TRL-1/2 into a TRL-3.

• It is suggesting that — with further work — it could deliver electricity rate of 9 cents per kilowatt hour, whereas the Lazard 2017 price estimate for utility-scale ground mounted PV electricity was about half that (4.3-5.3) and the record (unless it’s been beaten since) is 2.4 cents/kWh.

• What I have read about the Retro Directive Phased Array is that it is it an assistant for good actors, not that it is a safety mechanism. By analogy, it seems that saying it makes this system “safe” is like claiming the passive aerodynamic stability of a 747 will prevent it crashing into a building — not the claim made by the inventor.

RDPA looks to me like a nice improvement to a traditional phased array antenna. Phased arrays can be re-aimed dynamically without physical rotation — which is, I think, why it’s being used in this design.

• The link itself suggests using its own wireless power transmission tech as a substitute for wires (page 50)

• Their own estimate for an initial full-scale (1 GW) is “far term (20-30 years)” (page 65) whereas their “mid- to far-term” market opportunities are the $0.5-$3.0 per kWh range (page 51)

$0.5/kWh is worse than combining batteries (~$0.18/kWh) with 5.4 times as much ground-based PV.

• The construction costs for the 2 GW plant “With aggressive tech advances“ are estimated at $16 per Watt (page 83), compared to current ground mounted costs of $0.103-$0.278 per Watt according to PV EnergyTrend on October 31 last year.

• Check out that risk-impact matrix for the 2 GW “mature” design on page 95

• The ground receiver is estimated to cost $10/m^2 on page 79; Unfortunately page 70 says “Determination of the actual power received will require additional, more detailed analysis“, which makes me wonder what the claimed costs per kilowatt hour even refer to. (Transmission? But there are estimates of beamed power efficiency…)

I’ve not seen estimates for the size of the ground station in that document, I’m going to have to handwave this one and say that the ground station is a 10 km diameter circle (because that’s the value that I’ve seen in other analyses of space-based solar power), which gives 2 GW / (π (5000m^2)) ≈ 25 W/m^2, which is both a bit higher than I’d be comfortable with and simultaneously so low that at $10/m^2 = 2.5 W/$ = $0.4/W, even the ground station alone is significantly more expensive than PV ($0.13/W).