Send something into an elliptical orbit so that it gets much closer to the sun (or other star/energy source), and then returns to rendezvous with the sender.
Running low on energy? Launch that "Comet Energy Transport" sphere on its path, and in a few years, you'll get plenty of energy
as you meet up with it.
You could send these out every month, and collect & harness the energy from a "hot one" each month (with ~100 in orbit at any given time). Nice space juggling.
There are numerous ways to convert the energy from being close to the sun into usable forms for a spaceship or planet. Do the conversion en-route so you don't have any thermal losses. So I won't bother going into this part.
And space is a good insulator, so you won't have to worry about transmission losses much (unless you're silly enough to build it out of ice that melts away and leaves a tail like real comets).
Oh, sure, you can just sit back and put out solar panels, but then you'd be harvesting only the highly dissipated (inverse square law) energy from afar. The benefit of the comet transport is that you send something in closer to get that highly concentrated energy.
Highly renewable since all you'd be doing is casting a little shadow on some places that probably weren't going to use that light.
And you needn't stick around just our Sun, but if you were travelling to a different solar system and exploring that, you could use that sun, or any "nearby" energetic object.