Solar can produce a great many kWh per month if you cover the roof of a whole Costco sized warehouse with it, but for instantaneous power is nowhere near sufficient for large ship propulsion. The energy density in joules per kg or liter of fuel in compressed gas or heavy fuel oil or diesel is significantly higher than what is now possible with batteries. Where pv might have a role is shore bases charging stations to charge short distance electric cargo ships, such as the privately run ferries that transport tractor-trailers from the Vancouver metro area to Vancouver island.