Should I wire solar panels in series or parallel?

2 Posts
Aug 25, 2011 08:07 am
Should I wire solar panels in series or parallel?

So if I have 2 identical KD135SX-UPU panels (17.7v Max Power, 22.1v Open Circuit) and I’m charging a 12v battery bank (4 @ 6v, or 6+6 & 6+6), if the controller is capable of handling 44.2v of input from the panels…
Is there an advantage (or disadvantage) to connecting the panels in series to get 35.4v into the controller, instead of 17.7v in parallel?

The 2 advantages I can think of so far are:
1.   Less voltage drop from the panels to the controller (given the same wiring).
2.   As the panel operates in reduced performance, the voltage might drop below a desired charging voltage of say 14.4, if wired in parallel, but would say well above that if wired in series.

Am I on the right track, anything else I should consider?


462 Posts
Aug 25, 2011 03:14 pm
Re: Should I wire solar panels in series or parallel?

John, if you are charging a 12 volt battery setup, I would think you would want to use a 12 volt supply from  your panels. So parallel should be the way to go. Your controller has more to do with the battery than the panels so it too should be set, if it has a setting, to 12 volts.
 The power gained is in Watts so it really doesn't matter if you change voltage or amps, it will still come out the same, W = V x A, so if you increase amps, voltage will drop and vice versa, but the watts will be the same.
 What charge controller do you have?
8 Posts
Aug 25, 2011 04:49 pm
Re: Should I wire solar panels in series or parallel?

Hello John,
How you wire the PV modules will depend on the type of charge controller that you are using.  Just because the charge controller manual says that it can handle up to 44.2V doesn't mean that it is able to step that voltage down to the 14-15 volts that a 12V battery bank would want to see for proper charging. 

It is likely that the charge controller is capable of charging a 24V battery bank with a 24V nominal PV array.  That would explain the maximum input voltage of 44.2V. 

There are more sophisticated charge controllers that are capable of stepping down a higher PV array voltage to a lower battery bank voltage.  This type of controller is called an MPPT controller, and while they are more expensive than other types, they actually do provide a gain in charging current over their less-sophisticated counterparts. 

If you had this type of charge controller, then you could potentially wire up the 2 Kyocera KD135SX-UPU modules in series.  This would help with voltage drop along the wire run, as you mentioned.  I would only consider this method if you were CERTAIN that the charge controller is an MPPT controller, and the PV array input did not exceed the maximum power input of the controller.

To echo the other comment from Tom, what charge controller do you have?

Eric Pedersen
AltE Staff
877-878-4060 x141
eric @
2 Posts
Aug 25, 2011 06:13 pm
Re: Should I wire solar panels in series or parallel?

Thanks Tom/Eric,

I hadn't bought the controller yet, but was planning for an MPPT. So far I'm leaning towards the Rogue MPT-3024.

462 Posts
Aug 26, 2011 01:03 pm
Re: Should I wire solar panels in series or parallel?

John, that controller is capable of using a 12 or 24 volt input to charge a 12 volt battery, so I guess either way could work, series or parallel. Might as well stick to series since you only have two of the panels to reduce losses and reduce wire size. A little expensive though with all the bells and whistles. Check some controllers here at Alte for price comparison.
26 Posts
Aug 30, 2011 10:55 pm
Re: Should I wire solar panels in series or parallel?

If your controller can handle it, and an MPPT one could, then you should connect them at the highest voltage (series) that is within the charge controller's specs.  This is for just the reasons you pointed out.  Matching the voltage from the panels to the batteries is not a concern with an MPPT controller... getting the most efficiency from the panels through the wiring to the controller is what's important.

That said, you also want to think about future expansion capabilities.  If you want to be able to add a single 12V nominal panel at a time, say every few months, then adding them in parallel would be the way to go.  If you connect your first two in series, then you can only expand your system in multiples of 24V nominal.  E.g. two more 12V panels in series with each other, and the pair in parallel with your other pair.  Or if you can add a third in series, then you have to expand in multiples of 36V and so on.  Any parallel strings must be at the same voltage.

My system has the strings of panels at 48V.  I started with 4 12V panels in series, added a string of two 24V panels in parallel, and then later added another string of 4 12V panels in parallel to the other two strings.  I found this to be manageable and my Outback MX60 handled each configuration fine.  My batteries are at 24V.

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