Sailing things right

Splitting panels to separate controllers was the right decision.
Panels were connected in serie before, hence if one got even a little shade from the backstay the whole setup loses quite a significant amount of output. It's just physics, can't be fixed.
Here at the picture you may see that one panel is generating ~15% more energy than another. The starboard one is shaded by the backstay, which is just a 10mm cable, but since the shade stripe goes over all the panel, it loose a lot of output.