Just my two cents:
I live in Czech Republic, middle of Europe. Most relevant is it is an Dfb type climate (see here:
https://en.wikipedia.org/wiki/Humid_continental_climate)
We have in average 20-25 degree Celsius in summer and -5 - 0 degree Celsius in winter. 1500 hours of sunshine annually in average.
Even in these conditions, when I did research for my parents house (2 person), solar heaters pay-off time was 8 years, comparable to air-water heat pump.
Now I live in appartment house heated by air-water type heat pump. Since I moved we already changed our heat pump compressor once. According to technician who changed it its ifespan is 8-12 years. Add bi-annual inspection for coolant leaks, while solar heater is almost "build and forget" type.
More: Below -5 Celsius is our heat pump basically unusable due freeze buildup (spending too much energy in self-defrost cycle), and during summer is overkill (you can heat water just with garden hose lying on your roof).
Adding complexity with solar heaters is nonsense - you add complexity in both cases.
Heat pumps are cool and in, for sure, but I agree with redpoint5. Solar heaters are imho more cost-effective.