If your average solar array gives 2.5MW per hectare then 15MW would require 6 x 100m x 100m to run, or a beam of 150m for a 400m long vessel (eg Evergreen G-class.)

That’s only ~4x wider than the current big classes of ship. Maybe we will see twin hulls with a solar field slung in between?

The downside of course is you can no longer romantically sail by starlight (or at least, technically, by the starlight of non-Sol stars.)

Though a smaller array (just covering the deck of a current ship) could provide some boost - 25% isn't nothing, though you need clear skies to net that, I suppose we could consider a system when the ship would make a journey more slowly, stopping to charge for four days, sailing for one (though I assume drifting means you can't really "stop" entirely so that's not entirely practical).