Solar arrays are used by all spacecraft for general power generation, but fusion plants are required to power gravity drive propulsion and any weapon systems. Wind is pretty useless outside of worlds with atmosphere, which are pretty rare, but 95% of the Martian civilian power grid is supplied by wind farms and trials are being run for enormous low-orbit 'wind mines' around Jupiter. Subterranean AI-operated fusion stacks provide power for most civilised worlds but a lot of the older habitats and colonies still use molten salt fission reactors.