Gas heating without solar thermal?

yes, one of them...

Hello Björn! Well, if the solar thermal system had only cost €3000, you could have almost completely financed it through the €2500 KfW premium. The remaining €500 could have quickly been covered through the free hot water supply. But okay, you did write that it was about optical reasons for you.

Yep, the main reason was aesthetic reasons. Financially, it wouldn't have necessarily made sense either, since for KFW55 we would have had to pay an additional expert who would check the KfW implementation, which we did not have to do with KFW70. These additional costs alone would have almost consumed the €2500 subsidy.

...the remaining 500 € could be quickly earned back through the free hot water supply.....

Quickly? You can even heat hot water for a long time with gas using that...

Wrong, you are allowed to do without solar thermal energy if other measures reduce the Energy Saving Ordinance by 15%.

Of course, you are also allowed to build with other saving means. You have now given up on solar, but you installed your super insulation instead. But that also costs money to achieve KfW 70. The next one uses photovoltaics. If I combine, I pay more but might achieve better values mathematically. Your discovery is not that innovative,

No... it's actually basic knowledge when building a house...