Extraterrestrial civilizations need a great deal of energy as they advance up the Kardashev scale. Fossil fuels are finite, wind and solar energy are carbon free but not as efficient as fossil fuels, and traditional nuclear fission power depends on a supply of fissionable material and has a waste problem. Thus, any advanced alien species may well turn to nuclear fusion for their ever-increasing energy needs (unless they've discovered even better energy processes we don't yet know about).
