Solar is way denser than an RTG in terms of power per kilogram, at least out to Jupiter and probably to Saturn as well. This doesn't mean that RTGs don't have

Solar is way denser than an RTG in terms of power per kilogram, at least out to Jupiter and probably to Saturn as well. This doesn't mean that RTGs don't have value. They are continuous and keep things warm, which may be very important depending on your mission.