2 days
I saw a story about a similar car carrier with solar panels, basically they’re used to offset the hotel load of the ship, and have nothing to do with the propulsion.
Which is still a significant improvement considering how much time a vessel like this spends at port loading and unloading.
They very much are, depending on what you’re towing, most of your fuel used goes into overcoming aerodynamic drag. If you tow a load of gravel on a trailer, compared to a caravan of the same weight, the difference in fuel used can be double.
Towing something that’s not very aerodynamic can easily double your fuel use, which means half the range or less in an EV.