Weight won't matter much (you typically only accelerate it once, and the additional drag is small), it is just that the surface area is so small relative to what's needed that it just doesn't move the needle.

From the current top comment on this thread:

> It's made out of aluminum instead of steel. The resulting weight savings make it a bit more efficient. That's something this shipping yard specializes in.

According to that person, weight does indeed matter.

Solar panels are also made from aluminum frames or can be flexible in plastic sheets. The weight is negligible.

Yes, the weight of the hull, which is immense. Compared to that some solar panels probably weigh about as much as the paint. It's still ship, not an aircraft.

Also, thin film solar panels that can be stuck to a flat roof likely weigh less than the small portion of the battery capacity (250 tonnes of batteries total) they could theoretically substitute for.

If you were optimising for mass rather than ease of maintenance you'd probably put them on (despite the relative lack of surface area meaning you still needed to recharge at each end)

Drag is huge for boats, especially in seas and oceans that have tides and currents. Far more than a car... that also have to continuously burn oil to keep their speed, even on freeways.

See my other comment...

Weight matters for handling, particularly CoG and weather. It likely also has an impact on total cargo capacity.

There's also the matter of windage and what impacts that might have on the ship.

To say nothing of the capacity factor and reliability of electronics in a marine environment.