upgrade solar thermal

Hello,

In my planned new building, I initially intended to install solar thermal energy for heating domestic hot water. Is it possible to connect additional solar thermal panels after a few years to also support heating the building?
The VITOSOL 100-FM from Viessmann is being used.

Sure, but then you also need a new (larger) storage tank or an additional one. And the extra piping and safety devices. Where else do you put the hot water in summer?

So I wouldn't do it, it's pointless... you don't save anything because you have to deal with it twice anyway.