Since we’re vying for the pedant throne, I’ll point out that an ion thruster that is powered by solar cells would need consumable propellant rather than fuel, since it isn’t providing energy through chemical or nuclear reaction
And the suitability of solar sails for intersteller travel is limited by the fact that as you get further from the sun, the acceleration decrreases because there is less light falling on it. The proposals I’ve seen for this posit using lasers based in orbit to send more light to to the sail. Of course the lasers required to get to another star in ~100 years would require more power than our entire civilization consumes at the current time.
edited to add: which is definitely more efficient than carrying propellant with you, but as they say space is really, really big.
