I think you could do a lot with this. In the real world, there's no such thing as free energy. It doesn't really matter how it's explained (maybe capturing neutrinos or something), but keeping the energy system intact or modifying it to meet new demands could be interesting. It might be limitless, but nothing is without flaw.after the discovery of free energy
One thought I had was that space travel would basically consist of much the same but the free energy takes the place of fuel, so the ships could in effect just accelerate directly to the destination then turn around and decelerate; early experiments would include sudden full acceleration that basically pulverised everything or perhaps launched the vessel into deep space (and maybe it returns?). I like the ZPMs from Stargate and the handwaving of subspace bridges but I would have it more commoditised, perhaps making it more devastating if they suddenly stopped working.