More efficient to spend the same amount of money on shoreside panels with lower installation costs.

Do you have solar panels on top of your head? If not why do you leave that space unused? Space being there is one of the worst possible reasons. That bloats designs and makes them expensive to build and maintain.

Same reason EVs rarely have solar panels; adds weight and complexity, making it more expensive than putting the panels somewhere less wet and salty.

Talk to a marine engineer about the overhead (equipment, training, emergency procedures, etc.) of adding a small-scale solar plant to all the things that they've already got to deal with on a ship.

And recall that this bridge - https://en.wikipedia.org/wiki/Francis_Scott_Key_Bridge_(Balt... - will need a multi-billion dollar replacement, because the tiny engineering staff of a huge freighter could not diagnose and correct a surprise electrical failure. Within the maybe 3 1/2 minutes between the initial fault, and when the collision became physically inevitable.