question

timo-1 avatar image
timo-1 asked

8 Panels (east / west)

Hi,

I have 8 panels (200W, VoC 20,25V, Vmp 18V,Isc 12,68A). 4 Panels are facing south, 4 Panels west.

What is the correct way of "plugging" them together?

  1. All 8 in a row, with one MPPT 250/60 (or would i loose Ampere during morning times, as 4 panels are in shadow)?
  2. 4x2 (4 in a row) with one MPPT 150/30 connected via Y cable (or is the MPPT not able to find the maximum / best MPPT point for those two strings?)
  3. 4x2 (4 in a row) with two MPPT 150/30

As option (2) is of course the cheapest option, I would of course prefer that one..

Thanks a lot!

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2 Answers
marekp avatar image
marekp answered ·

@timo

The best way is to install two MPPT chargers. One for each direction.

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timo-1 avatar image timo-1 commented ·
@MarekP thanks for the answer. That is ofc also a pretty expensive one :-)

How will option (2) behave comparing to option (3)? Much worse (like 20% less power) or only a little worse?

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nickdb avatar image nickdb ♦♦ timo-1 commented ·

The least performing bank will drag down the overall performance, so dual mppt's are best.

Each side should be their own bank.

In the greater scheme of things, divided out over the years you will own it, the additional mppt doesn't skew it that much financially.

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timo-1 avatar image timo-1 nickdb ♦♦ commented ·

@nickdb : also thanks for your answer. What is a little bit confusing for me - I thought there are Schottky Diodes inside the panels (mentioned above) which will prevent that the very low amperage of the "shadowed" solar panels are affecting the overall amperage. Or am I missing something?

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klim8skeptic avatar image klim8skeptic ♦ timo-1 commented ·

Current is directly proportional to the Sun's irradiance the panel receives.

irradiance.png

Voltage produced from different irradiance levels is not proportional.

If you have 2 identical strings facing different directions, it is important not to wire them in series.

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irradiance.png (293.6 KiB)
timo-1 avatar image timo-1 klim8skeptic ♦ commented ·

@klim8skeptic thanks, that helps. Last question (because i have the same situation in a different place :-) ).

I have 10 panels in a row, all facing south, but i could add one panel facing west. There is simply no way adding that panel (not with diodes or whatever), because it will always harm the current of the other 10 right? So I must "waste" the space / not use it (one panel does to get the required voltage to load the battery), right?

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klim8skeptic avatar image klim8skeptic ♦ timo-1 commented ·
If you had 11 panels parallel up, you would need an awful amount of fuses to prevent the 10 south panels setting the 1 west panel on fire.


You could probably come up with other creative arrays/mppt's to use all 11 panels tho..

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tom4x avatar image
tom4x answered ·

Use MC4 plugs with diodes to prevent a current into the shadowed panels.

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