Nuclear fusion. The main problem today is superconductors' size. You need space for refrigerator circuits, that are not superconductors. If superconductors op

Nuclear fusion. The main problem today is superconductors' size. You need space for refrigerator circuits, that are not superconductors. If superconductors operational temperature are high enough, you could just refrigerate the entire room. Making superconductors more dense and powerful. Making fusion possible in extremely small spaces and making it even cheap. That is you could do fusion expending millions instead of billions.