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Jens Weber avatar image
Jens Weber asked

combining serial and parallel PV panels

Hello,

I'm planning a system with 4 arrays PV, feeding in a SmartSolar RS 450 / 200
For each Tracker I want to use at least 10 I'M Solar 430W (IM.S-BI-430M+80-BT10/54). Max 10 in series are possible 38,82 Voc(V) resulting in PV max. voltage @min. temperature of 423,5V. This resulting in PV power ratio of 93%. Isc(A) is 13,81A so I can't put them in parallel (2p5s or 2p6s) because max. PV operational input current is 18A. But I want to increase PV power ration because of low radiation in winter time and would like to go up to 130%, as allowed from victron.
My question: If I put 10 panels in series and for 1 of the 10 panels I put 1 in parallel, is that a way to go? Do I then add 13,81A/10=1,38A, resulting in 13,81A+1,38A=15,9A in total? Or if I add 3 panels in parallel (13 panels in total) do I get 13,81A+1,38A+1,38A+1,38A=17,95A. If my thoughts are correct I would be right under the 18A max. PV operational input current of the SmartSolar RS 450 / 200.
Or could this kind of putting panels togehter result in a general problem for the MPPT?

Thank you in advance for your thoughts and input.

Jens

Solar Panelrs 450
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Jens Weber avatar image
Jens Weber answered ·

Further research told me: the PV panel with the lowest current rating determines the maximum current delivered. That said the panels added in parallel would be wasted, because the current stays at 18,81A all the same.

Is that correct? So I would end up with 10 panels in series for each tracker?

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Jens Weber avatar image
Jens Weber answered ·

13,81A not 18,81A of cause

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pwfarnell avatar image
pwfarnell answered ·

Your additional input is correct, you can not parallel up a few panels in a string and the current would be limited to the flow through a single panel.

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JohnC avatar image
JohnC answered ·

@Jens Weber

Not sure why you'd want to do this anyway.

4 strings/trackers of 10 x 430W panels is 17200W. The RS 200A into (say) 57.6V is 11.520W. That's like 150% 'overclock'.

It's still ok though. Victron's 130% is just a typical value, not a limit.

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Jens Weber avatar image
Jens Weber answered ·

@JohnC

Ok thats true. What I just don't understand is why the Victron MPPT sizing calculator states "93% (undersized)" for each tracker? I understand that each tracker can do 80A but all together the RS is limited to 200A, is that because Victron did that because each array could give different input, like tracker 1 20A, tracker 2 80A, tracker 3 40A and tracker 4 60A = 200A.

So undersized is only related to a single tracker but when you look at the whole system, when all 4 PV arrays get full sun that is the "propper" value to look at when I want to know oversizing?

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ejrossouw avatar image ejrossouw commented ·

@Jens Weber This is the specification. Not 80A per tracker, but 20A.

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JohnC avatar image JohnC ♦ commented ·

@Jens Weber

Re that '93%', there's an Information icon there you could take a look at. My guess is that it's saying the tracker can only handle 93% of the panel rating. Each tracker can only output 4000W, and that's 93% of your 4300W applied. https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-MPPT-RS-EN.pdf

The RS is obviously designed to handle strings of perhaps different orientation, shade, panel numbers, etc. So yes, like you say re delivering the total. You could even consider reducing panels in certain strings, depending on your installation.

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