multi-directional array

65DegN

I have a customer that wants to put up 4 modules, one facing east, two facing south and one facing west. Rather than buying four MPPT controllers I was considering putting a schottkey blocking diode on each directional array and using a single controller. 
Wondering if anyone sees any complications with this or has used this approach. Thanks

MichaelK

I think a better solution would be 6 panels wired in a 2S3P configuration.  Then have one set facing East, one South, and one West.  If all the same voltage, you only need one controller, though 3 parallel strings should be fused or breakered.  This would tend to mitigate overloading the controller at noon, but broaden the net amps produced over the course of the day.  So, the one controller wouldn't have to be as large.

Alternatively, just wire them all in parallel, 1S4P, but then you'd need 4 fuses or breakers.

65DegN

The reason I was thinking of using blocking diodes was to prevent the negative effects of shading. I have found that if 25% of an array is in the shade it drops the output of the array by about 60~75%. The blocking diode would prevent that.  I do not have the liberty to alter the array size. 

Dave Angelini

Quality panels already have the diodes. You are overthinking this part. Solar panels should only be shaded by clouds or the virtual track of an east and west array. Sundown is the last reason

The part you are right on is a mppt can get fooled by an east and west array. Clouds can cause it to pick the wrong mppt V. In your case with small arrays it is not going to be a problem. The issue is real for a 3KW east and a 3 kw west array, especially for clouds.

65DegN

OK, so with a parallel configuration and one panel being shaded the shaded panel cells will be reverse biased and just appear as a high resistance.
Not sure how an MPPT controller will deal with this but it probably won't be too far off.
Thanks for helping me think this through guys.

Dave Angelini

It is all in the MPPT algorithm. Some are better, but they can get fooled and will try and correct.
The ones I use by Schneider are marketed as shade tolerant. They correct in less than a second for max power point voltage.

mike95490

Just posted an answer to this on another board, done right, it's great:

I know several folks using multiple arrays (virtual tracking) and they are fine.
  Each string MUST be identical - panels & VOC, or the controller can get confused easily

Bruce - from another board, has lots of land, time and machinery, and has built many arrays
with harvest documentation about how they work with virtual tracking.

starting with post 25 in this long thread, it gets into the meat
https://www.solarpaneltalk.com/forum/solar-panels-for-home/solar-panels-for-your-home/13861-sun-hours?p=163376#post163376

(Of course the reason the Bruce gets some many hours of "producing sunlight" in one day is due the way he has set up his panels. One group is facing East, another South and a third West. So for most of the day at least one group is producing.
It is a very impressive system. Great job Bruce. )

Dave Angelini

You can also skip all of the virtual track issues and electronic track like the Pro's do....