[lbriner]

And what do you do for the 6 months of the year when there is not enough solar to heat water to a suitable temperature?

[zurn]

People living in arctic areas with multi-month polar night generally already have some other heating energy source, as it gets a bit chilly. But in the summer they can have 24/7 solar energy!

There's not many people living in these areas though like the sibling comment points out.

[bluGill]

Depends on where you live, but generally this is enough solar, you just need enough well insulated storage to last a few weeks.