Heat pump - Domestic hot water preparation

Photovoltaics will be installed on the roof anyway. It will probably even be a KFW40+ house since, as you write, the storage is practically given for free through the additional 5,000 euros. Then just keep the storage as small as possible. They are simply not economical yet... I'm currently installing a 24.5 kWp system on my current house, but without storage.

Hot water storage tank is clear, what is Stumpf?

a) There are rules about how big the storage has to be. Your solar technician can tell you that
b) A metal can with 200 liters of warm water inside :P

We have 350 liters of hot water, but 3 people, a rental apartment, and a rain shower. I'm not worried about legionella.

Hello,
I'm just jumping in here.

There are 5 of us and I like to shower for a long time. It can easily be 15-20 minutes. Accordingly, we need quite a lot of water – but we have hardly any space in the utility room.

According to the building contract, a heat pump from Rotex, model HPSU compact or Vaillant, model flexo Compact is planned.
The installer wanted to install a Weishaupt WWP LS 8-B R-E for the same cost.

Now I have compared the storage volumes:
HPSU Compact: 300l
flexo Compact: 171l
Weishaupt: 165l

Even if the HPSU probably doesn’t have the best energy values and also uses hot water for defrosting, it still offers the most hot water.
Or am I missing something here?
Which compact devices from other manufacturers also have a large integrated storage tank // what alternatives do you see?

Best regards
Simon

Or should one then plan an instantaneous water heater directly behind the heat pump, which can also handle preheated water (compatible with solar systems)?