HumanPenguin , 11 days ago

As someone fitting solar to a small boat.

Both is an option. IE have a water tank that can heat water on lower power slowly. Making use of reusable energy. And a heat bump to efficiently use it. (Not really doable on a small boat)

And fit gas (i use electric) instant water heaters at the taps. I have it set up that I can turn it on and often use if when connected to shore power in winter.

But use a tank heated by a solar dump when possible.

Given how cheap solar panels are now. (£69 for 410w panal plus shipping) if your able to fit stuff yourself. It is worth the effort.