multi-directional array

65DegN
65DegN Solar Expert Posts: 109 ✭✭
in Advanced Solar Electric Technical Forum #1
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
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #2
    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.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
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  • 65DegN
    65DegN Solar Expert Posts: 109 ✭✭
    #3
    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. 
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,904 ✭✭✭✭✭✭
    #4
    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.
    "we go where power lines don't" Sierra Nevada mountain area
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  • 65DegN
    65DegN Solar Expert Posts: 109 ✭✭
    #5
    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.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,904 ✭✭✭✭✭✭
    #6
    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.
    "we go where power lines don't" Sierra Nevada mountain area
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #7
    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. )
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,904 ✭✭✭✭✭✭
    #8
    You can also skip all of the virtual track issues and electronic track like the Pro's do....
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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