Ok, so in your opinion it is better to rely on a heat pump (air-water heat pump) and a good photovoltaic system. Right? And why?
Correct, heat pump + photovoltaic. The type of heat pump that makes sense is provided by the results of a preliminary basic assessment (actual demand (capacity, energy) for heating and hot water). For higher demand, for example, a ground-source heat pump with vertical probe(s), surface or trench collector will be effective. With moderate to low demand, the better annual performance factor of a ground-source heat pump is less important, so here an air heat pump is quite sufficient.
...Is the efficiency of a solar thermal system really to be disregarded to such an extent?
Efficiencies are performance-related "snapshots" and are therefore less interesting. For the operator, the
energy-related annual utilization rate is more important.
Example: A heat generator based on the combustion principle has a combustion or boiler efficiency of 95%. The annual utilization rate of the system, however, is only about 60%. 40% of the input (purchased) energy is lost without any benefit. What value does this efficiency now have?
Example controlled residential ventilation: The manufacturer specifies a heat recovery of 80% (performance-related). The actual utilization rate, depending on the climate region, is only about 30...40%.
Example solar thermal system hot water: Although the energy source (sun) is freely available, only fractions of it can actually be used practically. Problems here are the "storage issue" as well as the daily course of the sun’s power supply (not constant). In a commercial operation where hot water consumption is distributed over the day, a solar thermal system makes sense; however, in a single-family home where the residents leave in the morning and come back in the evening, it makes less sense! Certainly, some kWh are "harvested" over the course of the year, but this yield usually bears no relation to the demand or the investments necessary for it. The theoretically nicely calculated energy efficiency mostly exists only on paper (e.g., KfW verification).
...In your opinion, should I leave out the solar thermal system entirely or only use it as a support?
Leave it out entirely and focus on the essentials! System installers often already have problems designing even simple configurations energy-efficiently because they often omit an adequate basic assessment, planning/dimensioning of the system. The more components involved in heat generation, the worse the overall utilization rate despite sometimes quite high investments.
v.g.