Yes there are, where you need *much* more power going upstream...
I deliberately didn't mention that, because it makes the numbers look even worse...
Water heating can easily be done by having the generator connected to a calorifier heating coil -- if you have a high-yield coil (which is not standard, but is what I'm doing) then that 1 hour per day of generator running will also give all the hot water needed. Or if you're not moving there should be enough spare solar power to provide this via an immersion heater.
If you need boat heating -- not in summer, obviously -- and you haven't got spare solar power then you also need a heating system, and a diesel boiler is the usual way of doing this since you already need a diesel tank for the generator. Definitely not solar either... 😉
The numbers for "solar-only" just don't add up, except for the case of not much cruising, slowly, in summer. For anything else -- longer cruising days, several days in a row, "normal" speed cruising, rivers, autumn/winter -- there just isn't enough energy available from solar, and a generator is needed -- plus some other heating method when it gets colder. And in winter solar won't provide enough power even if you never move at all on an "all-electric" boat.