One of the effects of having a wireless link to a solar water heating is that one can ponder about technical properties one would never have known they exist, e.g. initial temperature drop when the system starts up on a sunny morning, heat transport limitations or not enough noise to the sensor signals. It's good to know that none of that really matters - when the sun shines heat will be transported, and no optimization can replace sunshine :-)
The graph shows the collector and the storage temperature (in °C). The time span is roughly from 11:30 to 15:20 CEST (25/Sep/2018, Southern Germany, 5m² collector, 300l storage). The effect of clouds is easily visible. The storage temperature in the early morning was about 45°C, at the time of writing (15:40) it was 66°C.