question

bigboy529 avatar image

SmartSolar 100/20 MPPT, panels in series or paralel?

Hi all

I realize series vs parallel has been covered a lot, my situation isn't quite straight forward though so would appreciate advice.


I bought a camping caravan which came with the following 12V system.

1x 4KWH li-ion 12V battery

1x Victron SmartSolar 100/20 MPPT controller

4x 100W mono crystalline solar panels.


Panel specs

Rated max power 100W tolerance +-3%

Voltage at P-max 18.2V

Current at P-max 5.5A

Open circuit voltage 22.7V

Short circuit current 5.89A

Normal operating cell temp 47 +-2 degrees C

Max system voltage 1000V

Max series fuse rating 10A

Operating temp 40 – 85 degrees C

Application class A.


I want to permanently mount the panels on the roof of the camper but only 3 of them will fit, so my thinking is to permanently mount the 3 and then keep one loose which I can place out in the sun for example if camped under trees or on a cloudy day.


Option 1

If I connect the 3 panels mounted on the roof in series the VOC will be 68.1V and the current 5.5A which is still well within the limits of the controller. If I then add the 4th loose panel also in series, the VOC goes up to 90.8V which get’s close to the 100V max of the controller, this will also leave no room for a margen of 10% - 15% as recommended for fluctuations in temperature. Alternatively can I connect the 4th loose panel in parallel?


The big disadvantage to series connection in my situation is shade on the panels. At some or other points the camper will stand under a tree or get partial shade on the roof as the sun moves around, so I think parallel will work better.


Option 2

If I connect the 3 roof mounted panels in parallel the VOC will be 22.7V and the amps of the system 16.5A which is well within the limits of the controller. If I then add the 4th loose panel, the VOC will remain the same but the amps will go up to 22A.

From what I read inputting more current in to these controllers is fine as long as you don’t put in more volts, the VOC of 22.7V will be well within the limits so it’s only the 2 amps which will be out of spec and I guess waisted.


Is my thinking and understanding of these things correct and which in your opinion is the better option?


Nickus

MPPT - Solar Charge Controllersmart solar set-up helpinstallation
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6 Answers
WKirby avatar image
WKirby answered ·

Option number 2 would be your best option.
The output current of the controller is limited to 20A or around 250W on a 12V battery.
Given your potential shading situations you might not miss out on too much power. You can't really "over panel" an MPPT controller, it will take as much power as it can handle.

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bigboy529 avatar image
bigboy529 answered ·

Thanks for all the answers, in the end I'll be going with the 3 mounted panels connected in parallel since the main decider in my case is shading on the panels.


Another question, I was thinking to put a switch between the panels and Smartsolar controller if for some reason I want to switch off solar charging.

Will it make sense to put a switch between the panels and controller or is there a way to switch off the Smartsolar maybe via VictronConnect?

If I do put in a switch, will any switch able to handle say 25V and 25A be fine considering the panels will run around 18V and 18A?

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It's easy to enable/disable the solar charging with Victron connect, just go to settings, then battery, then you'll see the " switch" to enable or disable the charger .

Auntyjack avatar image
Auntyjack answered ·

If you think there will be tall trees in your camping areas then series probably wouldn't be the best option, to be safe I would only go 3 of those panels in series for that controller . You would get better results if the panels are angled towards the sun so portable panels can make better sense but they are more likely to get stolen or damaged, can be a chore dragging them outside then dragging them back in and storing them securely....

Pretty sure option 1 wouldn't work , if you mounted 3 in series on the roof you'd need another 3 panels wired in series then connect that set in parallel with the roof panels. All 6 panels would need to be exactly the same too. Means you'd need to buy 2 more 100w panels exactly same what you have now.

Another option ( with what you have now) is wiring them in series/parallel meaning wiring 2 sets series then wiring those 2 sets in parallel. So for that you'd probably have to wire 2 panels on the roof ( in series) and 2 made portable ( in series too ). That way you wouldn't overvoltage the controller input at around 45 volts max and the output current wont be an issue , would be max 5.5 amps ( with just 2 roof panels ) or 11 amps max for all 4 panels connected . In theory this will get the max out of your panels using the controller you have. Oh yeah make sure all solar panels are exactly the same specs brand etc if you are going series even its only 2 in series.

In the end if you think shading will be real issue then going the simple method of connecting all in parallel will be best, in practice you would be lucky to go over 18 amps with all 4 in parallel due to cable losses / shading / panels getting hot.

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ejrossouw avatar image
ejrossouw answered ·

Personally I will favour parallel. Use the handy Victron app to assess your configurations under the MPPT Charge Controller section. (You can enter your own PV values.) Exceeding the manuafacturer recommendations could invalidate a warranty. More importantly, check the cabling is capable of handling 22A in parallel as I this is where I would be more cautious. It results in heat and inefficiency or worse if not taken properly into account. Another important aspect of parallel is the start bat +5V to get the charge controller going and if you actually have higher voltages, the charger can actually start earlier and make a day last longer. That is of course if you go serie. The parallel option looks ok for it however and if you use MC4 connectors everywhere, you can experiment quite easily.

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bigboy529 avatar image
bigboy529 answered ·

Thanks for the suggestion, but at this stage I will have to use what I already have, buying a bigger controller isn't a option right now.

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GanLieber avatar image
GanLieber answered ·

Hi...you need the 100/50. The 100/30 will not be damaged, but the total output would be less.
An alternative would be two (one for each panel) 100/20. This is likely to be cheaper (although I have not checked the retail pricing). This option will provide slightly more total power and have redundancy. The drawback is slightly more complicated and expensive wiring, as wires from both panels need to led back to the controllers.

printed circuit board

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