multiple charge controllers for PV arrays

[Jedon]

I read an article where they had two pole mounted PV arrays next to each other hooked to separate MX60 charge controller so when one bank got partially shaded it didn't "draw down" the other bank. Is this a good idea and why?

So lets say I had 2 pole mounted arrays of 4 Kyocera 205W panels each, the panels are 6.17A @ 23.5v each so that would be 24.68A @ 23.5V if they were all in full summer sun. So if one panel was shaded it would drop the overall voltage down?

I don't understand the "drawing down" part.

Thanks!

-Jedon

[boB]

If you wire the two PV modules in series, and ONE module is at LEAST at the nominal battery voltage, or above, you won't need TWO MX60s or MPPT charge controllers.

The bypass diode across the shaded modules will basically take it out of circuit (short it out, not open it up), and the one that is not shaded will do all the work. An advantage of doing it this way as opposed to using 2 separate MPPT controllers is that

1) it's cheaper and 2) you are only dealing with the losses of ONE controller rather than TWO controllers.

If the battery bank is 12V and each module is 24V, this would be ideal, but the important thing is that one module by itself will have to power the battery when the other  module is being shaded.  So, if you had 12 V bank and 2 12 V modules in series, this would still work fine with one controller, as long as the MPPT controller tracks good, as an MX60 does (and a couple of others these days too)

One module won't really "draw down" the other one though... The Max Power Point (MPP) voltage will just come down with the diode bypassing the shaded one.  Without that bypass diode that is normally built into each module, it wouldn't work nearly as well.

boB