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adrianc avatar image
adrianc asked

Series strings connected in parallel with different shading

I am planning on installing 12 x 270W panels with 4 panels connected in series creating 3 strings that will be connected in parallel. I will have shade in the morning (winter) on the one string. The charge controller I will be using is the MPPT 250/100 (to allow for expansion). My questions are:

  1. Each string will be producing different amount of power as one string will be in the shade and the other two in full sun. Does the controller handle this?
  2. How many individual strings can be connected to this controller (assuming I am not exceeding the volts or amps of the controller?
  3. What is the difference between the Tr and MC4? I assume the connections? The MC4 seems to allow for 3 separate connections, so is it limited to 3 strings?
MPPT Controllersbattery charging
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solgato avatar image solgato commented ·

If the shading is going to be different across the 3 strings you should consider running 3 smaller charge controllers in parallel, adding a BMV to the system and creating a network connection for all components.

In this scenario, you want your series wired panel strings to provide as much voltage as they can to feed the charger to reach its input spec. You can either leave some headroom for adding an additional panel or panels to each string, or the better choice would be just to create a new string with its own charge controller should you need to expand in the future since the panels may be older/newer or a slightly different spec.

The other nice thing about going this route is now you have sub-systems, so if one charger goes bad or one of your panel strings is faulty, the others won’t be affected.

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rainerb avatar image rainerb commented ·

Hi,

I do not know if it was really necessary but for my MPPT 100/50 with two parallel strings (one shaded), I installed two MC4 solar diodes in order to "separate" the strings from each other.

At least this made some electrical sense for me and it works flawless for over a year.


Regards Rainer


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JohnC avatar image
JohnC answered ·

Just adding to Sol's comment (which qualifies as an Answer).

The mppt's have one tracker. The terminals of either type combine within to a single pv bus. So any number of strings within the unit's capabilities - usually total pv Imp (edit to Isc)) is what you'd watch for doing that.

A single mppt would work, but not optimally. Markedly different orientation/shade of pv 'sections' ideally deserve their own mppt. Not necessarily one per string, but one per section would work fine. That may mean looking at those future 'expansion' plans and deciding the size of the mppt for each. You could even drop to the 150/ models, so likely a max of 3x panels/string, or even 2x then, as suits your batts and pv numbers..

The mppt's can be of mixed size and panel configuration.

Many people would design for 'now', and add another mppt at expansion time. Your choice..


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MPPT Product Page

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MPPT 150/60 up to 250/70 Manual