Ready for season 10!
A new 200-litre boiler with two coils will be used from 2022. The upper coil is already connected to the heating system and in use. The lower solar coil is connected but not yet filled with water as the temperature is still below zero at night. The boiler is raised from the ground by 60 cm because the heating system is gravity fed. Here are a couple of photos:

Real-time temperature graphs will be available here:
Outdoor temperature, collector temperature, boiler temperature.

The season ended on September 23. The temperature measurement remains and awaits the new season.