Just to establish this, the whole "generate power in space and beam it to earth to distribute" idea is terrible and wouldn't work.
Generating power in space and then beaming it down (or through wires in some sort of tether) would require much more power then generating it on the planet would and is extremely impractical. A laser would be scattered very badly by the atmosphere and suffer massive losses, wires would get their asses handed to them by resistance (simple ohms law) and induction. Not to mention the fact that we just can't concentrate a powerful laser that much over such long distances yet either. On top of that, that large laser is going to generate a LOT of heat, likely several times the power it is emitting as a laser. How are you going to cool it? Your black body emitter is going to have to be city sized or it's just going to melt. A laser just simply wouldn't be able to do the job, so that leaves us with wires in some sort of tether, but that causes other problems...
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Well you got me on the laser, after taking a second look at the options available that is the least efficient. The best choice would be microwaves, I should have gone with that at first but laser are eye-catching lol
. If you guys want to go really in depth there is this article
http://www.sspi.gatech.edu/wptshinohara.pdffrom Georgia (US state not the country) tech, but I will just summarize their summery. So solar production has a theoretical efficiency limit of 70% and 30% is reflected into space (could not find % absorbed by atmosphere...). That means to be practical Space Based Solar Power (SBSP) needs to be able to wirelessly (for as veduher explained wires are impractical). Microwave transmission through an atmosphere has an efficiency of about 95% and transmission ranges of 148KMs have been achieved. If you do the math it comes out as incredibly inefficient in terms of power transmission to make it in space and microwave beam it down to you, mainly because of the small distances that you can transmit microwaves across, would require multiple transmissions in order to make it to earth. Now most of that loss obviously comes from the small distance you are able to accurately transmit microwaves over, the 95% rate is good by its self. Factor in the fact that 20-30% of energy is lost in the conversion from microwave to electricity and back, which is the real reason the retransmissions are bad because that is just from one microwave generator to an antenna, it would add up. The problem isn't really the atmosphere, microwaves in the wave lengths of 1 gigahertz to 30 gigahertz are almost unabsorbed by the atmosphere, which is why they are used for communications. The only thing holding it back from being more efficient than planet bound solar is the transmission range, if it could be transmitted over distances of 1000 KM, the length from the surface of earth from where the atmosphere really stops.
But on the subject of the laser as I said before that was a stupid mistake on my part, and I apologize. Now on the subject of the laser the one down side you didn't mention (you were quite thorough) is that you would have the same efficiency problem with photovoltaic on the ground, I.E. the increased loss of energy due to photovoltaic inability to convert light to power. Microwave to power is much more efficient.
The heat critique would still hold true for the micro wave emitter though. That would also require a large black body emitter, or be able to withstand high temperatures for short periods of time. Short periods of time because the thing doesn't operate constantly, it operates infrequently and thus would only be required to withstand high temperatures for small amounts of time.
Oh and on the subject of safety concerns, the emission within a reasonable distance (within a city block) from the receiver would only be mildly dangerous, and they would likely be built in areas as short as half a mile outside of where the energy will be consumed. Admittedly I made up the half mile mark as safe, but that’s a really conservative estimate because the microwaves are (relatively) very accurate.
Oh and all of this is without superconductors in the machines, which could likely be incorporated in them at the same time they become practical for power lines, which we have all agreed would be very, very helpful.