A Dyson sphere around a black hole

Better link: https://arxiv.org/abs/2106.15181

The results are fairly obvious: CMB and Hawking radiation provide almost zero power output, while an accretion disk and relativistic jets can provide a lot of power.

Oh cool, CC-BY!

In theory you can get an arbitrary amount of power from Hawking radiation if you have a lot of very small black holes instead of just one big one. I feel like the stability of the negative-feedback control systems for their orbits might be important here, especially if they're orbiting something you care about like your home planet.

As far as I understand, small black holes could be used as a super efficient energy storage („Kugelblitz“), but hardly as a source, assuming that primordial black holes are rare. Primordial black holes afaik are the only theorized origin of a sub stellar mass black hole at this stage of the universe‘s timeline.

Yeah, making tiny black holes could be pretty challenging, but I feel like it's just an engineering challenge. Is there a fundamental reason I'm missing that you can't just build a really precise, solar-system-scale particle accelerator to slam together a lot of mass into a tiny space to make tiny black holes?

It’s just too much mass in too little space. It’s essentially the same requirement as fusion, but almost infinitely more difficult.

If you could make a fusion reactor almost infinitely better then it would produce a black hole which would immediately evaporate releasing more energy than you could ever imagine - but no way it can be done.