After I found out (with the amazing support from initialstate.com, and correcting a previous comment, it is indeed possible to send events from the past. You just need a proper JSON request).
So I got all the data from March until now. I will devise a way to send the data I have gather since last winter as well. eventually. But, thanks to initialstate, I can see the difference a slightly better solar controller makes:
This is an uptime graph. The Y scale shows how long the machine has been up. The higher, the better. As you can see, it was pretty uniform until around may 15. That is when I changed from a shitty 6€ solar controller (never buy that shit) to a 12€ slightly better one (aliexpress link).
What you see is that I rebooted the P from time to time after May 15th, but just because I wanted to. The PI can run indefinitely with the amount of solar panels, batteries and cheap controller I have running it. Imagine what I can do with the second battery and a proper controller….