Advice sizing solar to solar charger

DIY
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1

I’m sizing my first solar charging system.

I have two Renogy 200w panels and may have room on the roof to add a third to my design, but the Voc = 37.44, Vmp=31v, Isc=6.85. If I use these in series, I will exceed the 100v limit of the Smartsolar 100/30. Vtot=112v > 100, correct?

If I use three in parallel, will my Vmp of only 31v be enough for a 24 volt system, that is, will it meet the threshold of Vbatt+5 with less than full sun to turn on and charge the batteries?

Is using the SmartSolar 150/35 the only way to work with these three panels?

2

I think you gave yourself the answer :blush:

yes you will need the 150/35, voltage is a strict limit on mppts

3

In addition to the reply relating to series layout if you put them in parallel then it is the Voc that is important for the start up because at start up, you have no current flowing, the controller has the panel open circuit, so the 37V should be enough to start so you could use the 100/30 in this case. The 150/35 will give you more flexibility.

4

Thanks for that. Would there be other benefits reaped from the extra investment for the 150/35 such as running cooler? I read that having PV 20v higher than Vbatt optimized the efficiency (?). Are these considerations worthy?

5

best to have an even number of panels and

then do a series and parallel connection

6

150/35 will run cooler. Not sure how Victron MPPT efficiency varies with PV voltage.

7

Thanks. That makes sense as I think through the math. I keep it in mind for next time.
Presently, I am roof/space limited and have 400w of PV and just eaked out room to add one more for 600w. Good idea, I figure, BUT it puts me in an unclear optimal sizing alignment with Victron options. That’s my dilemma.

8

i use 3 Victron mppt controllers

1 for my 4x100w Renogy panels a series/parallel connection

1 for my 1x 160w Heliene panel

1 for my external connector to allow an additional panel

why, each panel oem and model has different parameters