Large window front on the west side

You have to meet certain requirements. In the end, it doesn’t matter how the sunlight is. The north side is usually always less sunny. According to your husband’s logic, there shouldn’t be any KfW40 houses.

The best glass facade is never as "warm" as a good wall. Passive houses have glazing on the south side so that they can benefit from solar energy especially in winter. Ideally, the north side should have no openings at all. My husband fears that the west side doesn’t get enough solar energy in winter and that it will be very difficult to meet the KFW requirements...
Or are we just worrying unnecessarily?

Ok, true. That could be a point. But when I look at the plots, you can include the west (e.g., living room) and design windows open to the south (and large) (e.g., dining room and kitchen).

I would then specify a certain room arrangement for you during the house planning.

From my (layman's perspective), I still do not see it as problematic.

I still don’t understand what solar radiation has to do with a KfW40 house? You have to meet certain requirements. In the end, it doesn’t matter how the solar radiation is. The north side usually always gets less sun. According to your husband’s logic, there shouldn’t be any KfW40 houses. You plan a house as you wish, and then the energy consultant determines what is necessary to meet the standard — insulation, brick, type of windows, etc. Plus controlled residential ventilation and air heat pump, photovoltaics + storage, and done. That’s how it was for us anyway.

Exactly THAT is how it is! We planned our house and arranged windows arbitrarily. The energy consultant then gave a calculation and told us what and where/how we needed to insulate. At no point was it about changing a window or other component. Except for the north side, we have sunshades but no roof overhang, the roof is very well insulated plus a wooden facade with integrated insulation and of course the floor slab insulated, plus controlled residential ventilation, done. Take the plot you like best and plan your house according to your wishes/needs. Everything else can be managed afterwards. Regardless of that, I wouldn’t subject the floor plan or design to a KfW subsidy. If that were the case, I simply wouldn’t do it. But as I said, you are probably worrying unnecessarily about it.

I do understand that with "more about the Passive House," window area is planned facing the sun, meaning south, and small loopholes on the north. But the sunny side also partly includes the west... you don't have to glaze the entire side, but plan so that you have the view from the dining nook. A 2-meter-long window is enough, maybe also with a window seat. But I wouldn’t torment myself or give up the advantages of a plot because of that. You take that with you, you buy it with it – so you plan accordingly. First the plot, then the house. If you take that number too seriously, then it may be that you look for 10 more years for an ideal plot or never find one because there is always something.

It is simply the consideration of whether these plots should even be considered

Is there really that much choice with you? A plot with a view, and then also on the garden side – you take that with open arms!

It is important to me that I think early about a possible building site – with all the pros and cons...

Sure: but the house is adapted to the plot and the scale is not that of an unbuilt house.

The distance to the boundary would be only about 5.5m).

Precisely for that reason, you do NOT plan a house beforehand, but you plan the house ON the plot.

On the south side, we would have an HS window (approx. 400x250)

I wouldn’t like that either. Towards the neighbor, a ribbon window or a patio door may make sense, but not so open-hearted that you don’t feel comfortable. I would rather forgo the 40-plus model than a great plot!

our municipality will soon be selling building plots in a new development area. We are currently in the process of picking out the "best" building plots... I know... sounds very optimistic... we just have to name 5 building plots in the application that are suitable for us.

The location of the "favorite" plots in a row on the slope with staggered reference heights reminds me of the thread - maybe you will find some inspiration from it for your selection (?)

Is there that much selection with you? A plot with a view, and then on the garden side as well, you’d take that with open arms!

This is a new development area with about 35 building plots. 10 of them have edge construction facing west, about 7 edge plots are oriented south. The terrain is somewhat hilly, so not all plots are attractive (some, despite the edge location, lie very low).
Since we are a family with 2 children and live in the community, we have a good chance to get a nice building plot (by the way, price per m2 around 300€, so not exactly cheap).

That’s exactly why you don’t plan a house beforehand, but you plan the house ON the plot.

I fully agree with you. But if you had a certain selection, then you plan THE dream house ON THE dream plot ;)

A window strip or a terrace door might make sense facing the neighbor, but definitely not so openly that you don’t feel comfortable.

That wouldn’t bother me at all. There will be a hedge in between anyway. The neighbor would have me on his north side, so he certainly won’t plan a terrace right on the boundary.