Xantrex MPPT Charge controllers. At expansion, the PV on #1 and #2 will get merged into #2 with an added string. #1 will get 12 new panels (4 strings) on a ground mount ($$), pole mount ($$$), tracking pole mount($$$$), or wind turbine mast with PV tracking ($$$$$+). #3 will try to squeeze 5 strings onto it because 3 or 4 of the strings will be flat-mounted.

Expansion requires chimney lowering/removal and main panel upgrade and will be about time for inverter/charge controller / battery replacement.

I will seek to upgrade charge controller wiring to a 2AWG even though Xantrex says max 6AWG. 4x2AWG (2 for PV, 2 for batt) + 1x6AWG (ground) will fit code commplaint 1.25" conduit and will fit 1" with 60% fill. Can just use 1.25" conduit and use a reducing washer to connect it to a 1" knockout. It looks like the wire terminals in these charge controllers will fit 2AWG wire. Wire management is another store.

6AWG is code compliant for 60A continuous (90C) only with no derating - 1 circuit in the conduit (no more than 3 current carrying conductors) and ambient never exceeding 35C. 4 current carrying conductors in temps not exceeding 35C requires 4AWG. 4 current carrying conductors in high AZ temps (45-50C) requires 3AWG. I have 2AWG coming from the combiner boxes and spliced to 6AWG (positive in the circuit breakers, negative in splice blocks in the junction box opposite side of the wall as PDP) to comply with Xantrex limitations. The patio conduit (left-most controller) gets quite warm. This charge controller is the only full charge controller with 12 panels / 4 strings on it (all 4 controllers will be full at expansion). At expansion, Xantrex's 6AWG limitation is going out the door. The terminals look like they will fit 2AWG and that's what they are going to get.