Sure. They can. Assuming that they're not reliant on the power grid to back them up when their solar or wind isn't generating so well. But, even assuming ideal

Sure. They can. Assuming that they're not reliant on the power grid to back them up when their solar or wind isn't generating so well. But, even assuming ideal self-sufficient power generation, their Bitcoin are useless unless the rest of the blockchain participants confirm them. Which requires an interconnected system of networks. An Internet, one could say. And guess what? the infrastructure to run a national computer network, never mind an international one, also relies on the rule of law and the authority of nation states to provide continuous service.