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alex-2 avatar image
alex-2 asked

4 solar panels through individual MPPT

Hi

I have 4 x 175w Victron solar panels and 4 x 75-15 Smart MPPT

I was going to run each panel to it's own MPPT, that way if one panel is shaded it won't affect the output of the other three. Have i got that right ot am i best getting a bigger MPPT and connecting them all together in parallel to get a bigger combined output, or will the 4 individually give the same charge?

I'm no electrical engineer but a fairly competent DIY sailor.

The main battery bank in 4 x 100Ah Lithium and i am looking at getting an Orion Tr for charging them via the alternator and start battery bank.

any help or ppointers would be much appreciated.

Sorry, but i seem to be asking a lot of questions on here but i am loving learning and all the help available.


Many thanks

battery charging
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5 Answers
JohnC avatar image
JohnC answered ·

Hi @alex@alexalley.com

This is the optimum combo for applications like a yacht, with all sorts of selective shading like sails down to even rigging wires affecting output.

With one big proviso.. That panel V is much higher than battery V. So for 12V batts, a panel with spec of 17Vmp I'd call borderline.. might work, then maybe not at all. With twice that, like 34V, go for it.


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alex-2 avatar image alex-2 commented ·
Thanks for that John. The panels are Victron 12v 175 Bluesolar Mono Crystaline panels with a Vmp of 19.4v. Would that be sufficient do you think or build them in 2 sets to doulble the Voltages?
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JohnC avatar image JohnC ♦ alex-2 commented ·

@alex@alexalley.com

19.4V is better than 17V so might be ok. The trouble with putting the panels in 2x series is that you can only use one 75/15 on that string, so like 210W from a 350W panel potential (emphasis on potential).

If you already have this kit I'd try it 1:1 and see how it goes.

Light can do strange things. Sunup and sundown seems to me savage on Vmp, yet panel shade can still hold up V but lose output. The Vmp is important to get the mppt started.

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alex-2 answered ·

Thanks John

I already have the panels and the MPPT's. I seem to be spending all my time on the Victron website trying to learn as much as possible so I can build the right set up. (I also have to consider the alternator charging, AC plug in to shore power and inverter, as well as a DC generator - which i want to get rid of all together).

The bopat is already set up with 360Ah of lead acid as service batteries, but i want to replace them with 400Ah lithium (I already have 2 x 100Ah of Victron smartlithium).

I'm also aware that I seem to be asking a lot of questions on here and don't want to abuse the system. :-)


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JohnC avatar image JohnC ♦ commented ·

The questions are fine @alex@alexalley.com That's what this place is for. But it is great when they're well researched and the relevant data provided. Not so tedious to answer, and the answer can be better targeted.

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alex-2 avatar image alex-2 JohnC ♦ commented ·
Really appreciate that John and thanks for the help.

Ideally I want to and need to understand it all myself so I know what is going on in the system, rather than just pay someone else to install it for me and not really know what is where and what it does. If something goes whong at sea, i need to be able to fix it myself.

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neki avatar image
neki answered ·

If you put 2 in serial you will have double the voltage and same amper like on one. So voltage drop will be much less, and you will get more power from them. So it is better to put them in serial. You have max 9 A ( less in realiy) from each panel to mmpt. If you 4 paralel it will be 19.4V - 36 A. 36 Amp on 6mm solar cabel on 15 m its little bit to much. If you put 4 in serial you will have 77.6 V and 9 A max. For same system. And 9 Amps on 6mm cabel is more then ok. In both case you will get same Amps on battery max 175/12 x 4. Less in parallel, more in serial. + if you have low light, or shadows sometimes voltage drops on panel. If it drops on 15 V it will stop charging, if its serial it cant drop so much that it will stop charging. Of course if you put 4 panels on 4 mppt whit diffrent wires, it will solve ampers, but then you will in total have more loss then serial and it is easily go undervoltage.



For your case i will recommend 2 systems whit serial connection between panels. That you have backup, 2 system, but to take the best of connection.

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alex-2 avatar image alex-2 commented ·
Thanks Neki

So 2 panels in series (38.8v and 9A) going through a single 75/15 MPPT times two (4 panels and only using 2 MPPT?) is that correct?

daft question - will that give me 9A or 18A charge at the battery? obviously i want to maximise the charging capacity - but also want it to work efficiently as well. I will be living onboard and sailing around the Mediterranean.

I have also been looking on to DC-DC charger like the Orion Tr but have no knowledge of them currently (I have an alternator ont he enging and am considering using the currently installed 360Ah lead acid service bank as a starter bank - is that a silly idea???)

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neki avatar image
neki answered ·

It will give 9A on 38V ,

thats is 342 W to mppt,

in mppt that 342W it goes to 12V

342 W/ 12V is 28.5 A.


So you get 28.5 A to battery's


So you will need or bigger mppts or that you go whit 4 seperate panels on 4 mppt. 75/15 means that max voltage from pv is 75 volts and 15 is max amp what he can charge. The 70/15 is for only one 175w solar panel. In real world you will never get this number, it will always be less. If you can change that 4 for 2 bigger mppt then you go whit 2 system, if you can't just go whit 4 of them. If in the end you are not happy, then is easily to change just mmpts and put it in serial.

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neki avatar image
neki answered ·

Of course you can take mppt 150/80 and put all 4 serial on one. Important thing that every one of them give almost 15 Amp and that its total up to 60 Amp. So you can combine how you wish. Just if you put in parallel, tha amps goes up, and then the diameter of wire goes up too

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