It shouldn't be one thing, or 'only eco thing'.

It should be _every_ thing that isn't a bad idea.

Solar

Wind

Geothermal

Tidal power?

Got a way of using that tasty oil cleanly? Maybe we want to reserve those complex hydrocarbons for some other use like growing crops, making solid rocket fuel, or some other national priority.

Nuclear - Yes, craft regulations that make sense and squeeze all the damned energy possible out of that 'waste'. No, I don't mean burn the fuel the easy way only - I mean send it back to military run reprocessing centers to concentrate the power and make the (effective) half life of the waste decades rather than civilizations of time (yes, concentrating it, there will also be some super mild things that decay slowly enough to be useful in other applications rather than waste).

We want to maximize energy in the long, medium and short term. Try Everything.