MPPT100/20 12 or 24V questions ?

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dumbzh asked Feb 12, '24

MPPT100/20 12 or 24V questions ?

Hello Victron community ! 

I have a 70W 12V solar panel (I don't have the characteristics label) connected to a 100/20.

My battery is a 12V 100A AGM which I will shortly replace with the same capacity but with lithium technology

I would like to optimize the capabilities of the Victron controller as much as possible.

If I understood correctly, I need at most 12v X 20A = 240W

My question is the following :

- Add a 12V 170W panel in parallel ?

- Add a 12V 240W solar pannel to replace the old one ?

- Add a 24V 240W solar panel to replace the old one ?

- Can I add this 24V 410W panel (cheaper price), dangerous ?

Rated voltage: 24 V
Isc [A]: 11.12 A
Uoc [V]: 46.70 V
Impp [A]: 10.67 A
Vmp: 38.90 V

Thank u so much

MPPT Controllers

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Answer 1 · 2024-02-12T19:14:15Z

1234enough answered · Feb 12 at 07:14 PM

The 100/20 has a max of 100v input & 20a output, so any panel below 100v absolute max - allow bit of safety margin on this.

Put panel specs into https://www.victronenergy.com/mppt-calculator and tick "allow over sizing above 130%", this will then give recommend mppt for given panel.

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Answer 2 · 2024-02-12T19:40:58Z

dumbzh answered · Feb 12 at 07:40 PM

Already done but what I don't understand is on the instructions it is marked
PS: 12V: 290W 20A MAX
PS: 24V: 580W 20A MAX
On paper the last panel fits into the box but in the MMPT Calculator it does not. Above 290W it is no longer good.

Is the 580W at 24V only with a 24V battery?

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klim8skeptic ♦ commented · Feb 12 at 10:44 PM

@dumbzh Read note 1a) at the end of the tech spesc in the MPPT manual.

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Answer 3 · 2024-02-13T04:29:19Z

furyjk98 answered · Feb 13 at 04:29 AM

@dumbzh
If you are going to install this single panel. You are good to go. The MPPT will adjust the MPP of the panel to limit the max charging amps of the battery to 20 amps.

Rated voltage: 24 V
Isc [A]: 11.12 A
Uoc [V]: 46.70 V
Impp [A]: 10.67 A
Vmp: 38.90 V

So for a 12V battery, your charging amps will be capped at 240W-300W depending on the max charging voltage of the battery. However, if you install a 24V battery, you can get the full benefit of this solar panel, which is 38.9Vx10.67A = 415W

The limit for PV input for 100/20 MPPT is capped at 20 amps max before you start getting an error message or a fault. So if you are installing more panels in parallel, make sure the ISc rating of both panels added does not go above 20Amps.

Also, when combining two solar panels in parallel. Make sure the Vmp of both panels are very close to each other. It should be Within 5V-1V, so both panels can run at their Maximum Power Points.

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Answer 4 · 2024-02-13T09:47:56Z

dumbzh answered · Feb 13 at 09:47 AM

Thank you @FuryJK98 and @klim8skeptic

So I'm thinking of going with a single 24V 410W panel

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furyjk98 commented · Feb 13 at 11:50 AM

That's nice, and in the future, you can add another panel and increase your battery to 48V to push 1000W using the same charge controller.

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