Best PV configuration for MPPT 150/70?

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santana asked Oct 8, '21

Best PV configuration for MPPT 150/70?

I am upgrading the 4 solar panel array on my sail boat and I'm backing into the size of the existing mounting rack. I have found a manufacturer with two models of 210W panels that fit. One model is 12v, the other is 24v. The panels will be wired to a MPPT 150/70 and feed a 880 AH battery bank of 4 220A Victron gel batteries. My question is which of these models will give the best charging profile? And what is the best configuration to wire them?

I have listed the panel specs below:

12v Panels:

Voltage MPP Vmp(V) - 16.77V

Current MPP Imp(A) - 12.48A

Open Circuit Voc(V) - 19.83

Short Circuit Current Isc(A) - 13.09A

24v Panels:

Voltage MPP Vmp(V) - 33.54V

Current MPP Imp(A) - 6.24A

Open Circuit Voc(V) - 39.66V

Short Circuit Current Isc(A) - 6.55A

The current set up is 4 120W panels wired as 2 x series, 2 x parallel. Everything works ok in this setup, I am just looking to increase my charging capabilities.

Thank you.

MPPT SmartSolar

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Answer 1 · 2021-10-08T06:48:13Z

basil katakuzinos answered · Oct 08, 2021 at 06:48 AM

How about 5 strings of 3X24V pannels in series? (not sure if you can put 4, V might be to high)

Im guessig 200Watt pannels so 3kWp

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Answer 2 · 2021-10-08T07:04:13Z

JohnC answered · Oct 08, 2021 at 07:04 AM

Hi @Santana

Those 2 panels you've displayed look like they're identical, just wired differently.

What you need to do is try to match the Vmp of the new panel(s)/string(s) with that of the existing. A 'few' V difference can be lived with, but the closer you can get the more accurately the mpp tracker can optimize the whole array.

But we don't know what your existing panels are, nor how many new ones you plan adding. Battery V?

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Answer 3 · 2021-10-08T14:14:55Z

santana answered · Oct 08, 2021 at 02:14 PM

Hi John - To clarify the existing 4 x 120W panels are being replaced with the new 4 x 210W panels. Batteries are 12v.

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Answer 4 · 2021-10-09T04:19:53Z

JohnC answered · Oct 09, 2021 at 04:19 AM

@Santana

Ah ok, replacement.

I'd choose the '24V' panels, and you could go the same 2S2P stringing you use now.

On a sailboat though you may have shade to consider, and even the shade from a rigging wire on a single panel can affect the output of a string. If that's likely you could even run a 4P setup, and with 12V batts that should be ok. (That's why I wouldn't go 12V panels, as poor light will render too low a V).

With 4P though you may need to upgrade (or duplicate) your wire size from the pv, as the Amps will double from 2S2P to ~25A.

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Answer 5 · 2021-10-12T02:14:20Z

santana answered · Oct 12, 2021 at 02:14 AM

Thanks John. Your answer makes perfect sense. And I am planning on running new wires as part of the PV refresh.

Cheers.

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