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More to the point, why does that shop advertise to anybody other than gov agencies with deep pockets and a strong interest in remote sensing?

So in order to receive this beam efficiently, you would need a solar array 5 km in diameter with 100% ground coverage. Efficiency decreases if the array is smaller or less dense. Maybe you could use a curved mirror to focus the beam to a smaller diameter, but that seems more difficult than spinning a flat mylar sheet.

Assuming you had such an array, every 1 m^2 of mirror should provide roughly as much power as 1 m^2 of panels on the ground.