Microwave based power transmission systems do not rely on the photovoltaic effect for the conversion of the energy in the beam into electricity. Instead you use

Microwave based power transmission systems do not rely on the photovoltaic effect for the conversion of the energy in the beam into electricity. Instead you use something called a "rectifying antenna" or rectenna which can be 85-90% efficient[1]. If you put 1000 watts of power down on a square meter of a rectenna you could pull 850 to 900 watts out of it. Most of the proposed space-based solar power systems (SSPS) posit a reasonably large rectennas (like maybe 10 - 20 acres or 4 - 8 hectares) sized fields. The challenge is to make the field low enough density such that things flying through it aren't harmed by it. Fortunately energy density falls off with the square of the area so if you have a enough open space you can make it arbitrarily low power per square foot or meter. [1] https://en.wikipedia.org/wiki/Rectenna https://en.wikipedia.org/wiki/Rectenna