Proper storage for heat pump with photovoltaics?

Hello everyone,
we are about to build our new single-family house. Therefore, I ask for your help...

The question arises about the right storage system: layered storage tank with instantaneous water heater for hot water or buffer storage tank/domestic hot water storage tank:
Further, there is the question about the correct sizing of the photovoltaic system.

Here are the framework conditions:
New build with 190 sqm living space and basement
KFW 55 (1-liter house)
Decentralized ventilation system (97% heat recovery)
Heating: Novelan LAD 9 HID 1
Combination with photovoltaic system
No additional heat sources such as wood stove or solar

My heating installer has now offered me a 600-liter layered storage tank Novelan MFS 600 S.

Now the question arises whether especially for summer operation a domestic hot water storage tank with separate buffer storage tank would be better? Since then probably only the hot water storage needs to be heated. How large would you dimension this?

Would you still choose a heat pump tariff or would this no longer be cost-effective?

Thank you very much. Christian

600l is way too big. Underfloor heating does not need a storage tank, 80l per person is enough for hot water for showering. For hot water, you need 45-50 degrees, underfloor heating only 30-35 degrees. Too large a storage tank only needs to be unnecessarily heated and loses too much heat. Photovoltaics as large as possible. For the winter it will hardly be enough anyway, but earns good money during the rest of the time.
up to 6/16 Roadster 2.5 from 8/13
Model S P85+ Signature Red

600l storage for the heat pump, total nonsense. Tell the heating engineer a few words to arrive in the 21st century.

The size of the photovoltaic system depends on the budget, roof size/orientation/shading and the goal (return, ecological thinking, or what motivation). If self-consumption plays a role, which is usually the case today, then it would also depend on your own electricity consumption including the heat pump. Basically: the larger the system, the lower the price per kWp. Reasonable sizes are just under 7 kWp or 10 kWp.

You have to calculate the heat pump tariff yourself, as it depends individually on the supplier. It is not worthwhile here, if you read around in forums it seems to be the same for many.

600l tank for the heat pump,

In a household of 4 people and extensive showering by 4 people within 1 hour... Then that really might make sense as a hot water storage tank.

In a 4-person household with extensive showering by 4 people within 1 hour... then that might really make sense as a hot water storage tank.

Extensive ... how long would one have to shower at 38°C to empty 600l of hot water, typically 45°C. Although hot water is also produced during this time, if necessary with an electric heater. And on the other hand, the buffer tank spoils your annual efficiency factor due to the necessary increase of the flow temperature.

I'm not talking about the heating buffer. Better less than more there.

Today's rain showers easily use 20l/minute, two of those in the house and you need 1,200l at 38° in 30 minutes.

I can't calculate that exactly, but the tank will be empty because such an 8kW heat pump can't compensate for that. And the heating element...

You complain about a lousy cop but want to use a tankless water heater. Whoever wants to understand that, can.