Confused by online solar charge calculator results

DIY
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1

I have the option to build either a 12VDC or 24VDC 1500-watt solar system to charge my 12VDC 820Ah LiFePO4 battery bank comprised of two 12VDC 410Ah batteries. The idea is to connect three panels in series and then connect them in parallel.

  • 12VDC 250-watt solar panel specs: 18.90V - Vmp, 22.80 - Voc, 13.70A - Isc, 13.20A - Imp, mV/C=0.28%/C, mA/C=0.045%/C

  • 24VDC 250-watt solar panel specs: 36.90V - Vmp, 44.70 - Voc, 7.24A - Isc, 6.78A - Imp, mV/C=0.28%/C, mA/C=0.045%/C

The online solar charge calculator recommends a SmartSolar MPPT 150/85 Tr VE.Can for either version even though the Nominal PV power, 12V rating is 1200W.

Is this correct?

2

I believe that the calculator allows over panelling by up to 30%. You loose a bit of peak power bit not much in terms of overall yield for a cheaper controller. If you want the MPPT to be based on the max power of the panels then divide panel power by 13.5V to give a 110A controller.

The controller can handle an array with a higher max power rating as long as Voc is never higher than the controllers voltage rating and Isc is never higher than the controllers short circuit current rating. Both values are on the datasheet.

3

So as long as I do not exceed the SmartSolar MPPT 150/85 Max. PV Open circuit of 150V and Max. PV short circuit current of 70A it is safe to exceed the Nominal PV power, 12V rating of 1200W. Got it.

Thanks!

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