I wouldn't write it off.

There could be could add battery storage to be used during the journey. They could include wind turbines to add further power generation.

Also ships can go slower. In my limited knowledge of boats every extra knot takes significantly extra fuel. If we were bringing multiple power sources 'slow' cargo may be viable. And the has to be other ways to increase this function.

And there is always hybrid. Not all power has to be renewable sources. A solution could start with supplementing diesel driven thrust with some lower cost green power. Given diesel is 70% of shipping operating cost that seems a potential option.

I suspect nuclear (be it fission or - someday - fusion) would be much more viable for powering something at that scale in a "post-petroleum" scenario. There already are a couple fission-powered cargo ships out there, IIRC.

The problem is that safe disposal of nuclear fuel is nontrivial.

I'd like to add that cargo ships, while being very efficient in terms of how much they can transport over a unit distance given unit energy, require enormous amounts of energy.

See some resources:

- https://en.wikipedia.org/wiki/Energy_efficiency_in_transport...

- https://people.hofstra.edu/geotrans/eng/ch8en/conc8en/fuel_c...

Why not have solar modules in a shipping container form factor. (Maybe shorter in height though) and stack those at the top layer when loading the ship.

You could probably even find some ingenious way to run the current through the containers stacked umderneath to route the power. They are made of metal.