Development plan - Is it possible to enlarge the living area?

What was important to us:
The existing house is not exactly within the building envelope - meaning, if we were to tear it down, we would have to reposition the house - this causes problems with the small garage, which is directly adjacent to the neighbor's garage.
Furthermore, there are the setback areas, because the new roof structure will be slightly higher - this is not a problem as it is existing. I also already have the neighbors' signatures; it is no problem for them that we come about 40cm higher with insulation and the new roof structure.
I need an office as I mostly work from home, my wife will use the guest room as a hobby room, we often and gladly have multiple overnight guests, plus we like to celebrate.
The children (currently a 3-year-old, a second planned in the near future) should have as much space as possible, also to be able to retreat sometimes.
Modern technology is important to me, including KNX.
Underfloor heating (without cooling) with air-water heat pump, controlled residential ventilation, air conditioning in the upper floor.

Problems that we unfortunately cannot change in the existing structure:
The staircase to the upper floor is in the dirty area.
Second garage is too small - my old Jimny FJ barely fits, but as soon as that is gone and replaced by another car, it will have to be parked outside. The second garage is nice and large, but still too small for two cars...
I would like to have an additional cellar room, but actually, with storage space, space in the fitness room, the large garage and above the small garage, we have enough storage space.

What immediately struck me. You don't need photovoltaics in the north. It only gets sun in the summer with a poor angle of incidence anyway. But less electricity is needed then because no heating is required. I had marked a location for an additional carport back then.

Carport is not allowed, probably because we already have too much boundary construction. If it comes, then it will be later, now it's still okay, I hope my Jimny lives a long time.

I have calculated photovoltaic in the north for a long time or talked to some people. Especially in winter with light cloud cover, that is when the heat pump is running, the yield from the north is similar to that from the south. According to pvgis, the yield is about 50% of the south, but if you consider WHEN the yield occurs. It should pay off then. Prices for the modules have also dropped significantly, and if they are already working up there...

Photovoltaic yield in the north is 0 in winter. You do have a 45-degree roof pitch. Don't let anyone tell you otherwise.

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The yields in the north are zero for many months. It is probably realistic that yield is generated with diffuse light. But only where the sun theoretically reaches. However, this does not happen for half a year. If you have the money to spare, you can do it. In summer, you feed in. But it is not profitable. That could be the first item to cut if things get tight.

Sorry, but that's not correct.

Where did you get the data from?
It actually doesn't take into account that "diffuse light," meaning solar energy radiated from the Earth's surface and reflected down again by a thin cloud cover, also yields output.

I didn't think it was possible either until I saw the installations and actually saw the calculation models.

Yes, you're right when the sky is blue.

Luckily, all theory is gray.

The sliding door to the living room is too small for me; in my opinion, it should be about 1.2 m wide and made of glass (frosted). Here is how I have it.



The TV is also too small. They are planning 2 m wide.

I would completely fix the large window above the sofa.