Doing an install for a friend on a motor home, he has four 100 watt panels, and wants two wired series, and the other two parallel, all going to a single 40 amp mppt controller. He read on the internet that wiring two in parallel gave more charge in low sunlight conditions. I would think this would not work because of mismatched voltages? Or does the controller don’t care? All four panels are the same model.
If you want to combine sources in series, they all must produce the same current.
If you want to combine sources in parallel, they all must produce the same voltage.
Draw out the series/parallel arrangements, such that series strings are horizontal rows, and each module within the string is a vertical column. Or vice-versa if you prefer. If you directly combine panels in series and parallel, the whole electrical zone must be a rectangle on a drawing like this. Not necessarily a rectangle in the physical layout, but rather a rectangle in the logical layout. By electrical zone, I mean the group of panels associated with an individual power processing device, in this case a charge controller.
In the event that you deliberately mismatch the strings, the MPPT tracker and panels will have to find a compromise point on the respective current-voltage curves of the panels, in order to force current to be the same in series, and force voltage to be the same in parallel. It could be far away from the sweet-spot on the curve, that the MPPT tracker aims to achieve, which means all panels involved in the electrical zone lose performance.