Aside from efficiency, with cost of bringing stuff into space, i wonder how long it'll take until it could be competitive with other energy source (which produced entirely on earth).
The technology required aside, one big issue with it is this:
With many folks already (wrongly) raising hell about about the low power RF emissions from cell towers, what makes the researchers think that beaming megawatts of RF energy down to Earth from space is a good, safe idea and that it would be accepted by the public?
Are there really that many folks who actually do that? AFAIK people who oppose 5G and roughly similar technology is in minority. And if i read the news correctly, the energy (from space) transmitted to very specific area which makes government have easier time to convince people that it's safe.