Solar thermal system efficiency improvement

That naturally shows how individual an attitude and accordingly optimization can be.

Yes, of course there is no absolute setting for the heating system for house type X and resident Y. Everything is always very subjective and must be adjusted over time until it works as desired. Even two identical neighboring houses can have more or less significant differences in settings. Not only related to the topic of [ST]. But the entire HVAC system.

All right. I especially wanted to emphasize the aspect of Legionella protection. Is it theoretically sufficient to turn on the DHW heating once a day (for example for 1 hour) to address this issue? I don't believe that the ST alone is enough to heat the entire 300l tank to >60°C.

I don't think the ST alone is enough to heat the entire 300l storage to >60°C

With sunlight, it is, and quickly at that.

Of course it manages that, just not in winter. And the controller must of course be set so that it does not switch off beforehand. Otherwise, as mentioned, our gas boiler runs the anti-legionella program once a week, but of course that only applies to the upper part of the storage tank.

I have a 300l buffer tank, which is enough for 2 baths or 3-4 showers. From March to October, I only need to reheat a maximum of 3-5 times, and my collectors are not on the south side. However, I heat up to 75 degrees. There probably won't be any control system that can predict both behavior and weather. It works best with manual control, when you completely turn off the district heating and only switch it on yourself when needed. ST must then be set so that only the upper boiler area is heated first, and only when that is warm, the lower one. Legionella are not a problem for private households with up to 500l of water, and it is enough if the temperature reaches 60° every few months.