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sami-soisalo asked

Why MPPT sizing system is recommending 150/35 and not 100/50 ?


I have 4 ea of 140W solar panels, 2 in series and 2 parallel. I'm running a 12V battery system.

Unfortunately I purchased (before finding this sizing calculator) a 100/20 unit which works fine but can only take roughly 260W (13-14V x 20 A) so I'm loosin the other half of possible max input . I could put my two 220Ah batteries into 24V configuration and hence get the higher input from the system but my refrigerator and 230 V inverter are both 12V so changing them again would be costly.

So I have opted to upgrade the MPPT. But my logic (still learning) would be to go with the 100/50 model and not the 150/35 model. Would't I still be loosing from the 4 panels if I take the 150/35 version ?


Second question though is that as I have put the panels on V shape formation (first 2 set of panels are taking the morning sun, limited time around 12-14:00 both are fully lit, amd then the second set is taking the evening sun). All panels have double diodes. So in theory I'm only loosin for these couple of hours the maximum yield... so does it even make sense on upgrading anything ( Cost vs Benefit).

All help on this item would be appreciated

MPPT ControllersMultiPlus Quattro Inverter Charger
mppt-calculations.jpg (161.4 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·
2 x 100-20 costs roughly the same as a 100-50.

A no brainer, esp if you have differing orientations.

Load output terminals might be useful as well.

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sami-soisalo avatar image sami-soisalo klim8skeptic ♦ commented ·
Thank you for you input. As the four panels 2P-2S are approx 15m away from the "station" can I still use only the original 16mm2 cable and then just split it up at station end or would I need to separate the two panel sets all together and draw new cable pair for the whole length?

Do you have any idea though why the sizing tool would recommend me to go 150/35 and not the 100/50?

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klim8skeptic avatar image klim8skeptic ♦ sami-soisalo commented ·

Unfortunately you can not share the array wiring between two mppts.

"Do you have any idea though why the sizing tool would recommend me to go 150/35 and not the 100/50? "

Dunno. The calculator does not know you have 2 arrays facing different orientations, gigo...

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