You don't need to wait for the solstice. The Declination sort of flat tops either side of it within half a degree approx, so tilt angles the same between now and early July.
Your next task, should you decide to accept it, is run a comparison with the panels in parallel for 12-12 and MPPT vs PWM when ambient is 25C or above. (we will assume that makes panel at least 50C) Insolation the same for each but doesn't have to be at max amps, just fairly good and in the same conditions, to compare whatever amps you get each way.
I can only do this with 24-24 since I only have the one 24v panel, and I would like to see what you get. The "issue" is whether the higher panel temperature that reduces panel power will take away from the "MPPT advantage" compared with straight PWM that uses panel amps that do not reduce with high temperature.
There is no way for me to tell if my own results are unique (and weird?) without a separate example. Thanks
