Re: Panel Calculations
Serial vs Parallel... With MPPT controllers, it usually does not make a big difference until you go above ~2x Vbatt charging for Vmp-array--Then the charge controllers do become a bit less efficient (ignoring wire lengths and gauge requirements).
For shading--It is a tough one. Some folks would like to use everything in parallel (Vmp-array=~17.5 volts) and others suggest placing everything in series (for grid tied inverters, that is Vmp-array~400 VDC).
It is a complex issue in the sense that shading moves and is otherwise variable (winter/summer, RV parked in different locations/angles to sun, etc.).
One person here mounted his array in "landscape" because he would get snow on the lower frame of the panel. His cells were two groups in parallel, so the upper group was in full sun generating 1/2 panel power while the lower group was waiting for melt or a snow broom to clear.
More or less, even "minor shading" on a solar panel will take out "that string" of cells. If two strings in parallel, that will be 1/2 the current of the panel (a 12 volt and 6 volt battery in parallel with blocking diodes--The 12 volt will supply the power).
When you have panels in series... then you can lose the "whole panel" worth of power, but the bypass diodes allow the rest of the string to function (say two 30 Vmp panels in series with a 12 volt battery bank. Basically, Vmp-array drops from 60 volts to 30 volts when one panel partially shaded).
These are probably "worse case" examples, but, to me, indicate why a person should try to limit shading as much as possible (relocate panels/vents, cut vents short, raise panels, etc.).
If you end up with three panels (or other prime numbers that don't split well)--Just placing them all in series for Vmp-array~90 volts and be done with it. Keeps wire diameter down.
Another option of two in series and one in parallel--that takes two charge controllers to manage--Not cost effective.
Otherwise, three panels in parallel (assuming Vmp>Vbatt charging) will be OK--Just uses larger diameter wire and a combiner box with fuses/breakers for safety (3 or mare parallel panel strings need series protection fuses). If one panel is a longer wire run, use heavier cable--But current sharing is less of an issue with solar arrays. They are, more or less, current sources and will share current even if the wiring is not "identical" between parallel solar panels, assuming your voltage drop is not excessive (unlike batteries or voltage sources which do not share well with even slight differences in wiring resistance).
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.