Expand photovoltaic system on garage later?

The orientation of the roof is unfortunately not optimal...
And I am not worried about the neighbors, we only have one and he himself has 2 solar thermal modules mounted on his garage

And subordinate components, especially for energy generation, are often exempt in design statutes. We had to provide proof for the repayment grant to KFW max. 1 year after moving in. The photovoltaic system was only connected to the grid shortly before, and no one complained.

The orientation of the roof is unfortunately not optimal...
And I’m not worried about the neighbors, we only have one and he himself has 2 solar thermal modules mounted on his garage

What do you mean by not optimal?
I think you’re worrying too much. Very few roofs face directly south.

Post an oriented aerial photo with marked positions of the house and garage. More decisive than the orientation can be shading from your house and the neighbors or trees.

Hopefully that can also be seen in the picture.