Newly built single-family house KfW55 standard - How to heat?

So could you hang a completely normal water-based flat radiator in the bathrooms instead of an infrared heater and connect it to the heat pump heating system? So rather go for a larger photovoltaic system after all?

No, don’t do that. The flow temperature is too low for the radiator! You won’t get any heating output. I have a Kfw 40 building shell. My heating curve gives a flow temperature below 30° Celsius at outdoor -10°C. At 0°C it is around 24.5°C, what heating output should the radiator still provide? Not to mention the hydraulic problems you would cause. If towel radiators, then with an electric heating element decoupled from the heat pump. Then you can quickly heat the bathroom up on demand before showering.

180 m² living space

I would rather expect a maximum of 2 kWh electricity for a kfw40 house.

We were told that with an oversized photovoltaic system, you overproduce and that is basically lost when the battery is full (especially in the warm months). Also, I once read somewhere that the ratio of battery storage to photovoltaic should be about 1 kWp = 1 kWh.

Since you sell the electricity, which is much more profitable than storing it, nothing is lost. Also, a ratio of storage to photovoltaic size only makes sense at most as an upper limit. A storage larger than 3-4 kWh barely brings any benefit. In summer you don’t use it and in winter you can’t charge it.

No radiators. Wall heating means underfloor heating in the wall. Low supply temperature means 30 degrees or less. Radiators are not mixed with underfloor heating in new buildings.

In our offer, instead of an air-to-water heat pump, we have a ground-to-water heat pump. It costs about €7,500. Does anyone have experience with a ground-to-water heat pump? It is planned to drill 2x 90m deep. The question is whether the additional costs are worth it? To me, still a layman, it seems logical that heat can be transported better from the ground than from the air, especially in the winter months.

If at all possible and also properly planned and executed, then definitely preferred over an air-to-water heat pump or air-to-air heat pump.

Correct me if I’m wrong but the drilling still costs an additional five-figure amount, doesn’t it? Can that ever be recovered through improved efficiency? We are talking about 10 to 20 euros in electricity costs per month that you save that way.