Gas with solar thermal? Or heat pump with photovoltaics? Consultation

Thank you for this thread, I am currently also struggling with the same question. I have bought an old building from 1956, the upper floor is now being completely renovated with a new roof U=0.14, new windows, underfloor heating. The ground floor remains as it is for now because my grandfather still lives there, along with the radiators. Currently, there is an electric storage heater that consumes about €3600-3800 in electricity per year, for 2 inhabited floors with about 78m² area (minus interior walls). Basement is uninsulated. The facade was insulated years ago with 6cm styrofoam. When my grandfather can no longer live there, the ground floor will also be completely renovated with underfloor heating and new windows; a single-story extension will increase the ground floor living area by 32m². Now, of course, these are 3 different heating scenarios with existing condition --> renovation stage 1 (only upper floor) --> renovation stage 2 (including ground floor with extension). The heating system to be installed now should, of course, handle both renovation stages. I was actually quite sure that an air-to-water heat pump with photovoltaics and energy storage is THE solution. My architect and energy consultant are also fans of this solution. Unfortunately, I now have doubts, both about my energy consultant and the solution. So far, I have not seen any calculation for my heat demand; it all seems somewhat based on gut feeling and experience. After all, the KfW application for the individual measure roof was approved, so the guy cannot be completely wrong. The acquisition costs are of course enormous. For a 9.9kWp photovoltaic system with a 10kWh battery, I pay €23k fully installed. For the Wolf CHC10/400 air-to-water heat pump + 280l hot water tank + 50l separation buffer with piping and installation about €25k (only existing offer so far, seems a bit expensive to me). Also, I have the feeling that the separation buffer is undersized. Now I have read a lot, also the whole thread here and various other sources and clearly there are quite a few pros and cons. What really makes me doubt the heat pump solution is a study that examined heat pump systems in practice over 2 years with evaluated measuring technology. I am not allowed to post links, but if you google "Wärmepumpen-praxistest" you will find the study, in which Fraunhofer IBP participated, by the way. With these figures, it is of course difficult for me to make such a large investment, especially since it may be years until my grandfather is no longer there. I now think that I am better off with a gas condensing boiler and solar thermal, if only because I can manage renovation stage 1 with it, be more flexible and have much cheaper performance reserves available. Unfortunately, I do not yet have an offer for gas + solar thermal, but I think I will be ready and installed for no more than €12k. That is my thought process so far. I would be happy about comments and suggestions.

Such studies should always be taken with caution... Basically, this is a case of overthinking and panic. Photovoltaics have no place in the calculation because they finance themselves or generate profits. A storage system is pointless. Whether air-to-water heat pump or gas, you can calculate it in all directions, good, bad, the same – it doesn't bring anything. Both work, both require a reasonable concept. For radiators and partial renovation, better choose a gas heating system (if gas is available). However, the 12,000€ is also a simplistic calculation, because you still need the connection and a chimney. It should not be cheaper than an air-to-water heat pump.

Such studies should always be taken with caution...

Of course, but hardly with more caution than efficiency simulations of air-water heat pumps that aim to push an annual performance factor over 3.3 to receive BAFA funding. I consider the study quite solid, and if only an average annual performance factor of 2.6 comes out for air-water heat pumps in Balance Area 2, for the entire heating circuit including hot water only 2.2 on average, then I do wonder why I should be luckier with my system than the average. And even if I should be average, with a real annual performance factor of 2.2 I have significantly higher running costs than were calculated for me.

Basically this is a case of too much thinking and panic.

You’re probably right about that. I’m considering consulting another energy advisor. But maybe that’s really wasted money since the subsidy for energy consulting is only given once.

With radiators and partial renovation, better take a gas heating system

Yep, I also think that’s the crux of the matter. Many thanks for your opinion. A chimney is present, and we also want to continue using an existing wood stove. Simply because it’s so nice. Gas is available in the street, connection costs 2400,-€, offer is already available.

And even if I were average, I have significantly higher operating costs with a real annual performance factor of 2.2 than was calculated for me.

My air-to-water heat pump has an annual performance factor of 4.3 - I can't imagine that an air-to-water heat pump can be built so poorly that it achieves an annual performance factor of 2.2...

may I ask how you determine them? Do you have heat quantity and electricity meters installed in all relevant circuits?

And above all including pump power. Some internal meters in heat pumps only give you false hope ...