Simple interpretation of heating systems with heat pump

But not even a small storage to save solar yields for the evening hours?

You have 10, 15 tons of screed that can buffer heat. 100, 200 liters of water do nothing compared to that. Especially if you want to avoid generating high temperatures.

Would a hot water heat pump then be the better choice?

No, you only need that if for some reasons you don't have a "proper" heat pump. All current models can easily deliver 50° without running at their limits or becoming too inefficient. (between 35° and 50° supply temperature there is about a 10% efficiency difference)

But then I would still need the instantaneous water heaters ...

Also too complicated. Simply heat the buffer to the desired temperature. That works. Almost all heat pump owners do it that way. If you want to make it efficient, you take a hot water tank that is enough for one day (300 liters for 4 people, e.g.) and only heat it once at midday. That’s when it’s warmest and there is the most sun on the roof. Don’t keep the default setting where the heat pump always reheats immediately and has to operate around 50° four times a day (and at night).