Fission power was going to be "virtually free energy" in the early 1950s. We'll see what we'll see. And frankly, after a world war I can easily imagine a culture where living "off the grid" is considered quite a virtue in itself.
And fire. We use fire for so many things that we burn shit down by accident (OMG, we've never learned to control fire, let alone nuclear. Not that I'm anti-nuke).
I'll bet that with their manufacturing technologies, they can drop a windmill or a solar farm just about anywhere with minimal supporting infrastructure as compared to any kind of nuclear power generation.