>Will the power company believe you that your system will only ever provide a tiny amount of power?

A small guage wire (ex:24 AWG) is limited to low voltage use. The issue is that voltage will drop over distance less than a city block.

ref: https://www.cctvcamerapros.com/AC-DC-voltage-drop-cable-dist...

Think of it as a telephone line. They do fine for tens of miles. And you have no signal integrity concerns, merely continuity. (Though being able to launch a TDR pulse down it would be neat, since localizing breaks would become trivial.)

I wonder if a fiber would meet the definition...