I think a large problem is going to be space debris - debris from previous launches and defunct satellites.
When the idea of an orbital power station was first formed in the early days of space exploration, space debris was not a problem. These days there is a huge number of tiny objects circling the Earth at high speeds - like bullets being shot at random.
The larger the orbital mirrors are, the more surface area there would be for collecting space debris.
Sure, you could place them in higher orbit, but then the mirrors would not get as much protection from solar wind from the Earth's magnetic field.