question

Luca Barbierato avatar image
Luca Barbierato asked

Sizing PV installation: MPPT 100/20 or 100/30?

Dear all,


we are striving to install this PV model (link) with such characteristic:

  • Nominal Power 280W
  • Voltage 24V
  • Vmp 32.4V
  • Voc 39.0V
  • Imp 8.64A
  • Isc 9.27A
  • Max PV Voltage 30V
  • PF > 0.5
We will interconnect two of this panel in series, so this configuration will have such characteristics:
  • Nominal Power 560W
  • Voltage 48V
  • Vmp 64.8V
  • Voc 72.0V
  • Imp 8.64A
  • Isc 9.27A
  • Max PV Voltage 30V
  • PF > 0.5
Furthermore, the batteries interconnected are 2X12V 120Ah AGM batteries in parallel, so the overall system is 12V. I tried to calculate it with the MPPT calculator but I don't understand if the system voltage is referred to the batteries or to the panel. To conclude, I don't understand if MPPT 100/20 will be enough or 100/30 version is needed. Could you please help me in such configuration?


Kind regards,

Luca

MPPT SmartSolarsolar sizing
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seb71 avatar image seb71 commented ·

Your link is for a different panel.

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Luca Barbierato avatar image Luca Barbierato seb71 commented ·

I made a mistake. Here the correct configuration.


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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Luca Barbierato

The 100/20 isn't really big enough. 20A @ 14.5V (charge V, say) is only 290W. And even the 100/30 only equates to 435W, but the potential for more than that would be only really be exceeded in near perfect solar conditions.

To step up even further to a 100/50 would be a waste of money. The batteries couldn't handle the full panel output for long anyway.

The only real reason to go there might be to run loads at the same time, but that's up to you to justify.

There are 150/ mppts which fit in between, but they cost more.

The "system V" in the calculator(s) refers to the battery.

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Luca Barbierato avatar image Luca Barbierato commented ·

Since I will install the PV panel on the roof, without a correct inclination of the panels, you suggest the model 100/30? Or to step down the PV panels size? For instance, 2x200W.

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JohnC avatar image JohnC ♦ Luca Barbierato commented ·

@Luca Barbierato

I live with flat panels too. Don't downsize them.

The 100/30 is a great practical match for your batteries and seasonal/weather variations.

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