Best MPPT Controller for an Overland 5 Panels Setup

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Charles Gomes asked Dec 9, '20

Best MPPT Controller for an Overland 5 Panels Setup

Thanks to all the professional sharing great info in this forum.

I'm building an overland truck, after much work to find the panels I've come with a 5 panels configuration for maximum solar yield of 2250Watts in the roof.

The battery system is 24V matching most loads at 24V as well.

Here is the roof layout with 5 Sunpower SPR-A450-COM

What's cracking my head is: Should I use a single MPPT and put them all in parallel or make two series in 3S1P + 2S11P setup ?

The Solar calculator shows:

So far I'm leaning towards a single 150/85 in 1S5P module configuration. Yes I will need heavy wiring.

I was wondering if I could make a single module parallel part of the 4S series but looks like I can't as the panel maximum series Fuse is: 20A,

My plan B is If after testing the 1S5P does not perform well then I will have to change the 150/85 to control 2S1P and will have to buy a 250/60 to control the remaining 3S1p.

Please anyone experienced with MPPT Series / Parallel would provide a recommendation so I don't have to make a plan B ?

Note: Battery system is about 12KW and can charge at 1C so it will be able to handle full yield.

MPPT Controllers MPPT SmartSolar mppt charging solar sizing

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klim8skeptic ♦ commented · Dec 09, 2020 at 10:18 AM

I would choose an 150/70 smatsolar and wire your array up 2s/2s. For the 5th panel, an smartsolar 100/20.

Good luck.

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Charles Gomes klim8skeptic ♦ commented · Dec 09, 2020 at 02:22 PM

Do you think it's a problem to put them on 1S5P outside of having to run heavy wiring ?

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klim8skeptic ♦ Charles Gomes commented · Dec 09, 2020 at 06:18 PM

Fusing a 5P array will not be fun, as well as costly.

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Answer 1 · 2020-12-09T19:05:27Z

michelg answered · Dec 09, 2020 at 07:05 PM

Hi Charles ! I will go with 150/85 MC4 and do the connection this way :

You have 3 MC4 at the MPPT (30A/max per MC4), so 1 MC4 will be linked to the first PV panel, then 2 PV panels in // connected to the 2nd MC4, and the 2 lasting PV panels in // linked to the 3rd MC4 connector.

You put 3 circuit-breakers between the panels and the MC4 to protect everything, in case an issue appears with one of the PV panels, you won't be blocked with the rest. Using 6mm2 cables will have no issues transporting 20A (they are rated at 32A), you can find them easily in DIY centers, and put 2 breakers for DC (they are different from those for AC) at 32A each, and a 16A for the single panel.

This way, every MC4 will get the power, no overloading of the cabling neither of the MC4 connectors. A good point would be to add also a breaker for the 24VDC after the MPPT, so you disconnect the charge to the battery bank.

Have fun.

Michel

PS: my setup is using 6 arrays with 2 breakers and 2 MC4 connectors on a 150/100 MPPT SmartSolar. Think also to add a BMV-70X to check the status of your battery bank.

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Charles Gomes commented · Dec 09, 2020 at 11:15 PM

Thank you @MichelG that's exactly the plan. I think that should give enough energy above 26V to keep charging.

Do solar panels give fixed voltage and vary their current or the voltage drops as well ?

If voltage drops this panels will give me about 20-25 volts at 50% and that won't be enough to charge the batteries and then I will have to make then in series to bring voltage up to allow for charge.

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michelg Charles Gomes commented · Dec 09, 2020 at 11:55 PM

As far I have seen, the panels are giving around 52VOC, and 44Vmpp,, so you are far away of the 5VDC necessary for the mppt to work and charge the battery bank. Usually you don't have a fast drop, it is really related to weather conditions and location. Sincerely, you need 2 years to be sure of your setup : first year you will see if anything is not working as expected, then correct it, and on the 2nd year you will check if the correction has worked.

Take a look at the graphs, so you will see how the panels do interact with the mppt and batteries :

My solar installation

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Charles Gomes michelg commented · Dec 10, 2020 at 01:13 AM

Thank you for the link. It really helps.

You got me curious, how did you get your fridge temperature into the dashboard ? Custom built stuff or the fridge comes with it ?

I looked at the graphs to understand the voltage, here is today graph:

Based on your system 24V battery + 5V for MPPT today your system starter charging at 08:02 AM when panels voltage was 5V above battery voltage +-30V and looks like the batteries were fully charged around 13:00

It seems your panels are not just in parallel because voltage goes close to 100V

Would you mind sharing what are your panels and series/parallel config ?

Given your model it seems that having at least a series of 2 would help reach voltage beyond the Battery +5V required.

I calculated the Vmp_min for my panels and at 45 degrees celsius they should output 36Volts however your graph shows a non linear output.

From the vmp_min I would say it's okay to have the modules in parallel however your graph seems that in reality I might end up loosing some charge earlier in the day.

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