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felix1337 avatar image
felix1337 asked

Which MPPT for two 325 peak solar panel

Hello,

i want to buy an MPPT for two Solar panels for my "island solar power plant" (Heckert NeMo 2.0 325) which should be used in parallel with the specs:

  • Maximum Power PMPP: 325
  • Short circuit current ISC: 10,17
  • Current at maximum load IMPP: 9,85
  • Open circuit voltage UOC: 40,98
  • Voltage at maximum load UMPP: 33,29

The battery I want to use, is the Victron Deep Cycle Gel 220AH.

The MPPT Calculator recommends SmartSolar MPPT 150/45 MC4. but for me it looks like, based on the specs of the panel that this MPPT is to overpowered? Since the two panels do not have more than 100 Volts or 30 amps? (System Voltage is 12 Volts)


Thank you!





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2 Answers
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Justin Cook answered ·

@Felix1337, your array could be delivering up to ~48.14A of charge (under absolutely ideal conditions) to a 12v nominal battery bank, so for your application I would recommend the SmartSolar 100/50. Please note that this recommendation is only applicable if you indeed connect your two panels in parallel, not series - if you connect them in series then you'd be dangerously close to possibly exceeding the maximum 100v input of that model. In parallel, however, you'd be fine.

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felix1337 answered ·

Thanks @Justin Cook, @Riaan Barkhuizen, now I understand more how the system will work.

I thought the amaparage the solar panels will just be added to each other, but I forgot that the volatage also needs to be converted to the 12v (14,4) battery, which leads into a higher amaparage, therefore the 30s wouldnt fit.

So for 12volts I have: 54.16 Amps right?


So if I would switch to two batteries in series, (2x110 AH) to use it as 24V System, i could use a smaller MPPT? But on the other hand, I would need to use a 24V Converter to 230 ACDC, instead of a 12V?

For 24volts I have; 27 Amps?



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Justin Cook avatar image Justin Cook ♦♦ commented ·

@Felix1337, basic rule of thumb is total panel wattage/floating voltage (not nominal voltage), so 650w/13.5v=48.14A Obviously there's some wiggle room there, I select 13.5v as floating voltage for a 12v nominal battery bank because it's a decent midpoint.

Float voltage for a 24v nominal system would be around 27v, so 650w/27v=24.04A, so you'd want something like a 100/30 for that application.

You are correct though, if you put your batteries in series for a 24v nominal system, your inverter would then need to be a 24vDC to 230vAC; additionally, if you have any 12v loads in your system that would be connected to the battery bank, you would need a 24-12 DC-DC converter to power those as well.

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