[SEJeff]

ISRU (what you're describing) does require a large amount of energy to do at scale. Also, ISRU has never been at the scale required to fully fuel a rocket.

There is a decent writeup on wikipedia[1] on how difficult this would actually be to do ISRU on mars. The TL;DNR is 56,200 meters squared of thin film solar panels. Granted, solar power is roughly half as effective on mars as it is on earth, but still. For reference, an American Football field is 7,140 meters squared.

[1] https://en.wikipedia.org/wiki/SpaceX_Mars_program#Mars_prope...

[elihu]

(Note from the link: that's the requirement to provide fuel for one starship launch every 26 months.)