Air heat pump or use gas and solar?

100% not. Only a malicious neighbor who initiates an inspection, but I dare to claim that neither a building nor an environmental office will take action on their own, because initially everyone assumes the innocence of the citizen, unless an inspection or justified suspicion makes something else likely. Karsten

However, I really cannot deduce from the wording of the legal text what the solar system must be capable of and what not. Regardless of how likely it is that one will be inspected or not, I want to build a legally compliant house. If I wanted to build a non-compliant house, I would just use a gas heating system and omit the solarmodule. But the solar modules are only installed because of the legal situation. And I find it completely pointless to install them but possibly in a way that is not legally compliant. Or am I seeing this wrong?

You must comply with your building permit. This includes the energy calculation and the associated materials to be used. Build differently, then the range goes from fines to demolition orders. The latter certainly not because of a wrong solar cell.

Of course, the thermal insulation verification must be adjusted accordingly.

The GÜ does not provide any calculations. The architect once sent me the heating load calculation and according to his own statements received trouble from his superiors because an energy consultant found an alleged error in it, which I then forwarded.

I am basically convinced that building with the GÜ was the right decision; but when it comes to heating / building services, you are definitely confronted with the disadvantages of this model.

He must not withhold that from you. That is part of the approval documents, you are the builder, or is it a developer project? If you are the builder, you are also responsible for building according to the approval. In my calculation, which I do not have to understand, it precisely states, for example, which U-value the panes and windows must have, how many sqm of cells must be installed on the roof to ensure the renewable energy share, how the masonry must be executed, etc. I have to know that; besides, I also paid for it. Only if you know it and build differently on your property, presumably largely for aesthetic reasons, is it even worse. However, getting caught is rather unlikely. Karsten