Gas heating + solar system with extra storage?

Good morning everyone,

Living area 140m². All underfloor heating, no basement

I need a professional opinion on this. I was offered the following:

Wolf gas condensing boiler CGB with standard storage tank CSW-120
+ domestic hot water solar system incl. solar storage tank 200 liters

I am confused that there are 2 storage tanks. Is that normal? I always thought it was a combined storage tank? Shouldn't the system "work & communicate" together? Is the storage tank big enough? (We are currently three, another child is planned).

Is the Wolf system good or is there something better? (Vaillant/Buderus?)
Shouldn't the solar system be from the same manufacturer?

Thanks for your answers and clarification.

oh yes it is a Kfw 70 house.

Interesting... we also build KFW70, have 182sqm and were prescribed a 750 liter tank, although as far as I understand it serves as a storage tank for hot water and heating support... but the 750 liters don't sit well with me, I will have it checked again if it is really necessary...

We are also soon planning to think about building a house. Finally! :)

Then one should take care of sufficient planning/dimensioning of the system in good time, as soon as the building structure is defined.

...Are these extra storage tanks even necessary?

That depends on the system concept. For solar thermal systems for hot water, combination tanks are common. With heating support (HU), two tanks are more efficient than, for example, a "tank-in-tank" system (combination tank). However, with HU the risk of stagnation increases. Overall, for a single-family house, one should consider whether a solar thermal system is actually an economical investment, because the rosy calculation on paper rarely materializes ;-) Best regards

Thank you very much for the support!