Recovering value-added tax on photovoltaics through the general contractor

Tax liability is determined by the timing of the performance, in this case the time of acceptance. Therefore: yes, the [GU] must. If there is no individual price at all, it could of course become "difficult" to determine the correct price. Suddenly the photovoltaics were very cheap and he pockets the difference...

Photovoltaics was individually priced as a possible compensation for self-delivery during the offer phase (if only I had done that...), but not in the final contract. Therefore, this definitely has to be separated somehow. The general contractor is willing to do so, preferably the photovoltaics according to today's prices. Of course, there are other reasons for this besides mere kindness, which I might address later.

I’ll also jump in with a question if I may...
House contract signed autumn 2022 with the main contractor.
In it, option for photovoltaic system/storage at a flat rate xx gross, valid until work planning.
Work planning is currently underway and I am supposed to decide next week whether I want photovoltaic at the flat rate.
I am reading about the VAT issue for the first time today. What does the situation look like in this case?

Best regards GD

Does it say in the clauses that the prices refer to the VAT rates applicable at the time of acceptance? If yes, I would calculate with 19% for the construction services in general and 0% for the additional "Photovoltaik-Anlage". The latter would therefore only be paid net.

Yes, that is stated in the general contract...