Energy "concept" for old farmhouse

I just read about heat pumps again. Until now, this option had not been very present for me.

In the process, I read that the water-water heat pump works with a well. Can an existing well be used for this? There is a well available on the farm.

Is there a type of heat pump that is "best"?

With the theoretically available size of the photovoltaic system, a heat pump would make sense. Most of the electricity should also be available on bad days. Are you planning with underfloor heating? Heat pump is for low temperature...

Just googled "low temperature." Do I understand correctly that underfloor heating is quite sensible with a heat pump?

Just googled "low temperature". Do I understand correctly that underfloor heating makes sense with a heat pump?

Yes, even necessary to achieve a certain efficiency. A heat pump thrives on the lowest possible flow temperatures in the heating circuit. This also means that there should be no rooms left that require a high flow temperature to be warm enough, e.g. if there are only old radiators present. The flow temperature can be lower the larger the heating surface is. Ideally, the heating load for each room is calculated and the underfloor heating installed accordingly. Alternatively to underfloor heating, the heating can also be installed in the wall or ceiling. Proper insulation also helps to lower the flow temperature, but the heating surfaces are more important. In older buildings, this is typically complex. However, if you are planning surface heating anyway, then a heat pump is the most sensible choice. Additionally, a as large as possible photovoltaic system, which is worthwhile independent of the heating system.

The heat pump should match the heating load of the house; the brand is initially secondary. More important is good planning and avoiding typical errors in hydraulics (no buffer tank). You can find plenty of information online about this.

Thank you very much, I can work well with this information. I will now continue researching.

There is no heating system where you are not allowed to open windows.
I advise you to find an energy consultant who will look at the local conditions and create a concept.
A 20-year-old roof does not sound like particularly good insulation, and most of the heat is lost through the roof.
Underfloor or ceiling heating only makes sense with sufficient room height; how is it in your case? And how is the floor constructed?
Be careful, depending on which building components you handle (facade, roof...), you will then have to bring them up to energy saving ordinance standard.

Above the 1st floor, the ceiling should be redone and insulated. The attic including the roof should not be touched in this step. The attic has even more space and we really do not want or need that space at the moment. Especially since, due to all the outbuildings, we will not need storage space for the usual "stuff".

The house will be completely gutted inside. Floors and ceilings will be completely redone (yes, we are aware that this will be more expensive than a new build).

Energy consultant does not sound unreasonable. Are there recommendations for consultants in the Essen area?

Are there any recommendations

Search on the KFW website. Even if you don’t want/need any funding, it’s still nice to take advantage of it if possible. For that, you need someone who is "approved" by the KfW. We only became happy with the second one. So don’t hesitate to inquire/get to know several. Insulating the upper floor ceiling sounds good, then the roof doesn’t have to be done.