Many large freight ships are in the process of having rotor sails installed [1]. A rotor sail is basically a circular mechanism that uses the magnus effect to spin and generate propulsion.

[1] https://www.hellenicshippingnews.com/norsepower-unveils-firs...

There are some experiments with solar on boats for propulsion. Most recently I saw a 40' catamaran in Canada with about 4kw of solar, replacing the sails. The owner is claiming about sustained 60-70 miles a day during the long summer months there.

The catamaran has relatively low displacement however, compared to both traditional sailboats and freight ships.

Norway has been experimenting with battery powered ferries to make short, sub-10 mile trips, with good success. The main problem they've seen is that the power required to recharge the batteries can overwhelm local power supplies, so they've added industrial size capacitors to assist with fast charging.

I don't see 700'+ container ships being converted to solar without a complete redesign/rethink of their systems. Typically solar panels are mounted above the ship, and on a container ship, the containers are craned into the hold through the same airspace that any solar panels would occupy.

There are roll on/roll off car carriers with solar panels on top so they can use less port power when docked. Can spot them in SF from time to time.

You'd need 100-200 acres of utility solar to propel a panamax at cruising speed.

And it couldn't move at night. And would have reduced speed on cloudy days

I just can't imagine that a solar farm could absorb as much energy as a diesel motor of that size can output. Can someone with more knowledge on that spare some insight?

Yes, but they would be slow if operating only on solar power.