Well, the "mass" of the atmosphere has little to do with RF transfer efficiencies...though passing through the ionosphere certainly does. The 54% comes about due to very real limits on the efficiency of converting electricity to RF and back again. You can sort of consider that the upper bound of what can be expected from a satellite-based system. When it's all said and done, in order to deliver 200MW of regulated 60Hz to the grid is going to require them to generate roughly 600MW at the satellite panels assuming they can get roughly 50% efficiency through the beam (which is likely quite a stretch). And yes, I realize the amount of time spent in shadow is very small..hence why I went out of my way to "size" the earth-bound solar concentrator system to be twice the power rating so it was an apples-to-apples comparison.
If you liked the billions of dollars over-budget presidential helicopter, the bridge to no-where in Alaska, and other such amazing government programs..then sure...this is a great way to spend our tax dollars. Luckily, we actually have a Secretary of DOE who has a clue for a change...so we won't have to witness that.
If/when launch technology becomes "near-free" to at least low-earth orbit...then something like this might be feasible. A project such as this is sort of putting the cart before the horse. Dollar-for-dollar you are going to get a *lot* more power out of a terrestrial PV system in the proper geography than this proposed space-based system, never mind solar concentrator systems. At a 3:1 ratio just in panel area needed (which more than compensates for the additional solar incidence in orbit plus the 24-hour exposure), that puts a lot of PV on people's rooftops for the same money before even considering the cost of the launch or the ongoing expenses of maintaining the ground-based receiver station and the associated gear.
If the economics are/were actually there..I'd be all for it. Unfortunately, as an engineer who has a lot of background in such things...I just gotta shake my head for now. Once every rooftop has a PV system and solar water heater that can benefit from it, once we have developed solar concentrator facilities on all the eligible areas that we can, once we have fully exploited our wind corridors (both inland and off-shore) and once we have developed our geothermal and tidal resources....THEN talk to me about space-based systems if we need more juice. It's all about grabbing the low-hanging fruit first...not doing the most expensive option just because it's technically possible.