Different size solar panels - One controller or two?

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travlnmark asked Apr 18, '19

Different size solar panels - One controller or two?

I’m installing solar on my boat. At the boat show last week I purchased 6 SunPower solar panels. 4 are 170w (29.4V/5.84A) and 2 are 50w (17.7V/2.8A). I also purchased 2 Victron MPPT SmartSolar controllers. 1 is the 150/60-TR and the other is the 75/15.

My question is; Can I run all 6 panels in parallel thru the 150/60 or is it better to run the 170w panels in parallel thru the 150/60 and run the 2 50w panels in parallel thru the 75/15? I’ve asked many people this question and I still consistently get different answers. So I thought I’d ask the experts - You Guys! What are your thoughts, one controller or two?

By the way, in case it matters... I’m on a 2004 Hunter 466. I have lithium batteries (2 Relion 300ah each), a Xantrex Freedom Marine 25 (2500w, 130a inverter/charger), 80a alternator on the Yanmar 75hp diesel, the Xantrex LinkPro (300a shunt on the neg side of the house bank), and just installed the Simarine Pico system but still installing all the shunts.

Thanks,

Mark

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Answer 1 · 2019-04-18T20:20:57Z

Murray van Graan answered · Apr 18, 2019 at 08:20 PM

Definitely two controllers. You can wire 2 x 170w in series, and parallel the 2 banks on the 60A MPPT, and the two 50w in series on the 15A MPPT. Then just make sure the two MPPTs are correctly configured for your batteries

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porcini commented · Apr 18, 2019 at 08:32 PM

I would do it that way as well, but I'm wondering a little bit about the charge controllers.

A 75/10 and 100/50 would have been cheaper without any disadvantages. There are no benefits with the 150V controller. Even so it will work like that, of course.

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Answer 2 · 2019-04-18T20:57:37Z

travlnmark answered · Apr 18, 2019 at 08:57 PM

Thanks for the input. Based on your responses, I’ll be using both controllers now.

I had been planning on wiring the panels in parallel vs series because being on a boat, half of the panels will most certainly have some amount of shading as the boat moves around. In this situation, is wiring in series still the recommended/preferred way?

And yes, I agree that both controllers are a bit larger than needed but I was advised to go a bit larger to leave room for expansion in the future.

Also, assuming that I use both controllers, would I simply wire the outputs of both controllers in parallel and then go to the battery bank with one + and one -? My concern is that one controller may be dominant and the other may not do much. Should I be concerned about this? Or, is there some magic that takes place inside the Victron controllers that would cause them both to contribute?

Thanks,

Mark

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porcini commented · Apr 19, 2019 at 07:38 AM

As the bypass diodes only work correct when there are no strings in parallel it would probably better to parallel all of the 170W panels. In case of the 50W panels these should be used in series. Both controllers should get their own cable (voltage measuring). There is no magic at all, but it will work that way without problems.

And there are even good news about that: With the smartsolars a synchronisation (bluetooth) will soon be possible!

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