Hi Adrien!
Yes, You are right. Measuring solar power from cells are quite challange.
First, solar cell power depends on type of a load, hence the MPPT chargers idea. Secondly it also depend on temperature. (I am speaking just at electrical characteristics. I skip the physical placement of the cells to the sun.)
At the beggining I ve assumed that Ill use resistive load. This simplicity approach have many drawbacks but for now I just want to make on step done. Ill share my wiring diagram but please give me few days (hopefully this weekend) as I need to wrap it up and actually draw it on a paper (or in computer) because I didnt do this until now…
Kind regards and I am happy we could do this together somehow.
Piotr