Photovoltaics initially without storage

If the battery is really to be planned, the inverter must be able to do that. So either buy a new one then or consider it now, it costs about 1,000 euros more. Such a battery does not really make the matter more profitable at the moment. That is only for the green soul.

From 7 kWp you are subject to the smart meter obligation according to current legislation, i.e. costs about €100 p.a. Smaller systems are exempt from this. Yes, this will surely be adjusted at some point, but after all, we live in the land of vested rights

That sounds good. 7 kWp should cost around €9,100 net (remember, you first have to pay €10,829 gross, but you get the VAT back - liquidity is required though!). Photovoltaics and heat pumps fit together like a glove. The profitability depends heavily on the self-consumption of the generated electricity, and with the heat pump, you have a big consumer in the house. But here comes toxicmolotow's advice again, maybe build close to 10 kWp right away to generate at least a bit more electricity for the heat pump in winter. That practically goes 1:1 into self-consumption (a storage battery would just stand there uncharged/empty - completely unnecessary). For 10 kWp, you might have to spend a few extra euros, but the price per kWp should already be around €1100-1200 net.

How do you manage to save €7-10k on the basement? Earthworks?

11-12K€, at most 13K€. Net, of course. And it should rather tend towards the lower price, as certain effort in execution can be directly saved in new construction. But don’t be blown away if you also see completely different offers. The range is probably quite extreme in this industry and often you’re offered stuff that makes no sense at all. Google mainly provides a lot of advertising and glossing over.

Our sales department of the prefabricated house company is the only one allowed to have its own basement builder and not have to use the factory-owned one, whose prices we originally planned with... The price is therefore now at least 10% below the original offer...

I would interpret [Allerwertesten auf Eimer] rather as not optimal.

But I stick to it: if 10kWp works, then go for it.

The problem is unfortunately that the photovoltaic system does not deliver exactly when you need it with the heat pump. I will upload a typical "frost winter image" of a south-southwest oriented photovoltaic system 5.4kWp with 30° tilt in combination with an 8KW geothermal heat pump.

There you see the "problem".