There will of course never be a Dyson Sphere, or anything even vaguely reminiscent of it.

Instead, long before anything of such a scale would be conceivable, we will have hydrogen-boron fusion for unlimited energy, and moved industrial operations out to the Kuiper Belt, where the truly valuable commodity -- cold -- is abundant.

Suns and planets are for extreme rock-banging primitives.

Alternatively we could merge with the machines and all go virtual. But I am to believe that part of the humanity will remain explorers and will want to go beyond our star. That's where the physics kicks in. There simply isn't enough energy that can be mined and extracted from minerals.

Where do you hope to get your energy, beyond our star?

This is, presumably, after you have fused all of Neptune and Uranus. I guess you could start in on Saturn, or Planet X.

There are several options how to make harvested energy work for interstellar travel

1. Just beam it with a huge laser to the spacecraft (google for several proposed projects already in development and plans for launch) 2. Store it onboard the spacecraft and then use, with multiple options and different levels of today's technology feasibility like creating a small spinning black hole or creation of exotic matter for warp drive