KfW 55 or 40+ for new single-family house construction in Würzburg?

I like the underfloor heating and the climate, which I got to know over a long time at friends' places. So the choice was not difficult for me.

The minimum storage size is also specified:

The power storage must have a usable storage capacity of at least 500 watt-hours (Wh) per residential unit plus 10 Wh per square meter of building usable area.

Yes, I am aware of that; I am currently assuming a 2 kW storage, more precise information will be available only after the building application is approved.

Why is life different in the [Passivhaus]?