However, the engineering challenges for deploying such a mirror are huge. The mirror would have to be as flat as possible to properly reflect the light instead of scattering it. A mirror that large would be difficult to keep the reflected light aimed at a precise point on the ground. Also, a satellite with a surface area to mass ration that large would be affected by solar wind and other perturbation effects, making it difficult to keep in position. Electric thrusters might be useful for station-keeping, but they'd have to be placed in such a way as to avoid disturbing the mirror's smoothness. That could be difficult with a flexible mirror. The Echo satellites back in the early 1960s showed some of the challenges in regards to solar wind, and the biggest Echo was 41 meters in diameter. A mirror that large would also be a big target for debris and micrometeors. The mirror would have to be very thin in order to be launched, so it would be vulnerable to even dust moving at high speed.

The engineering challenges for generating the electricity on orbit and beaming it to the ground would probably be less than developing such a large mirror, though the challenges are by no means trivial. There has been significant improvements in solar cell efficiency and expected lifetime since those 1970s studies. Back then, typical space based solar cells were made of silicon, making them about 10% efficient. They also degraded at roughly 3% per year due to the harsh space environment. Newer cells are made of materials like gallium arsenide. These cells are much more efficient and don't degrade as fast as silicon cells. You don't have to build a space power station as a single satellite, either. Solar cells might not even be the best way to generate the power. It might be more effective to use concentrators to heat a working fluid that drives a turbine. Such a system would be heavier and more complex than solar cells but should offer higher efficiency. To save mass and to feature built-in redundancy, you might want to build a series of small collector/turbine assemblies and link them together, or perhaps have each unit feature its own transmitter to beam down the generated electricity. You could build several power satellites and co-locate them like what's being done with some of the newer communications satellites. Still, the real challenge remains to make such satellites economically viable.