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Solar is a better bet for energy in near earth space as opposed to batteries. That changes as you go out to the Belt and Mars, but even then a radio thermal generator (RTG) is probably better.

If you want to ship energy to Earth surface you want solar again. Generate electricity from panels, convert to microwave, beam to receivers on Earth, convert back to electricity, problem solved. And no, the beam density would not high enough to cook anyone.

Google "space based solar power" for more.

You're going to burn a lot more energy getting to and from the asteroid than what you'd be able to bring back.

If you need energy on earth, fission thorium.