When installing the NoIR camera module I accidentally cracked the ribbon cable (it was a bit too short...). A new (longer) replacement will arrive this week.
During test run it was a sunny day, thus with the solar panel, the operation time was 3h in the morning and another 2.5h in the evening (after recharging the batteries with mains power).
The next test run will start in a week on Sunday, July 25th at 10:00 CEST (UTC +2) with (eventually) another session in the evening at 19:00 CEST:
Hopefully with the NoIR camera and some software updates.
Thanks to all drivers that gave a feedback!