Technology

Part of the trouble with alternative energy sources is that ICE engines, and their liquid hydrocarbon fuels, are really very good at both energy density and power output. Trying to power a ship like that on just solar panels would be completely impractical, even if the entire ship had a solid roof of solar panels above it. It just wouldn't have enough power. For energy storage, batteries won't help much. Between their weight and their lower energy density compared to liquid fuels, it just wouldn't be possible to power the whole ship with Lithium ion Batteries. And that's even before concerns about seawater, corrosion, or thermal runaway are taken into account. Wind would not mean powering generators, so much as it would just be a return to effectively sailing ships, even if it's done with a more efficient airfoil type sail.

The long and short of it is, we're really a very long way from replacing the power source of things like cargo ships and aircraft. This is where things like alternative liquid fuels can be valuable. There have already been successful experiments in capturing atmospheric carbon and using sunlight (not solar electricity, heat from concentrated sunlight) to drive a reaction that transforms that captured carbon into a diesel-compatible fuel. It will always involve a net loss, as far as an energy source, but the resulting fuel can still work in systems that traditional renewables can't replace, while being as close to carbon neutral as possible.