See my post in the middle. A maser is an excellent solution.
Of course, such a powerful maser would be a large
piece of hardware, but not so large that one HLV launch.
couldn't park it in LEO.
One HLV might launch BOTH a powerful maser device
and a powerful laser...
If Earth is threatened by an asteroid, switch the orbiting solar-power
systems from the Earth-pointing maser to the outward pointing
laser....I don't think the people on Earth would mind an electric 'brown-out' for such an emergency task.
cheers.
Jake