Solar panels serial or parallel with MPPT controller

[Travelmonkey]

Hi,


I am a bit confused on the advantages of connecting solar panels in series vs parallel when using a MPPT controller to charge a 12 volt battery.  I've read a couple of posts in regards to the Victron MPPT controllers (I have a 75/15) which can connect several panels in series (in my case, up to 75 volts).  Is there any advantage to do this if the cable runs are not long?  The posts often state things like this type of battery (AGM, maybe) or this brand of battery (Trojan) like higher voltage charging.

On paper, it seems like my batteries would have a better chance to be fully charged connecting in parallel vs in series (more amps per hour going in to the bank).  What am I missing?

 

[tx2sturgis]

If you already have a couple of panels and the Victron, then the 2 panels in series will work well.

Yes there are various opinions, but the MPPT controller can (or should) deliver the correct voltage and amperage to keep the batteries charged, assuming you have balanced your power production to be more than your power consumption.

The Victrons have had some reports of mixed results, but I can't confirm or deny that. Mine seems to work well. 

And wiring from the panels is simplified a bit when running the panels in series. 

Of course a couple of downsides too: partial shading will drop the amount of power produced, and if one panel fails open, (not likely, but possible), then you will get zero power from the pair.

 

[Weight]

Unless you have a large solar array, MPPT are not much better. If you have high voltage panels, the MPPT can produce a bit more power. That is why folks use series connections as that doubles the voltage. You are better served with a quality PWM than with a cheap MPPT. I have 400 watts on the roof with a 45 amp PWM by Morningstar. The panels are parallel. If one has shadow, the others do not suffer.

 

[frater secessus]

On paper, it seems like my batteries would have a better chance to be fully charged connecting in parallel vs in series (more amps per hour going in to the bank).  What am I missing?

The missing piece:  MPPT runs the panels at max power and downconverts any excess voltage to amps.  As long as the MPPT's slight hunger for higher voltage* is met the bank will be fed everything your panels have to offer, whether series or parallel. 

Therefore  if MPPT's voltage requirements are met then one generally runs parallel for greater harvest in partial shade. This means we need to know more about your panels.


=== If the panels are nominal 12v (36 cell) poly or amorphous it might be best to run them in series due to the lower voltage at which they make max power (Vmp).  You could probably get away with poly/amorphous in parallel if you were going to stay in cool weather.   The reasons for this are discussed (for other reasons) in this thread. 

=== If the panels are nominal 12v (36 cell) mono you could probably go either way (serial or parallel) and it would make little power difference.  I'd might run them in series if you are likely to be in vast unshaded areas like deserts, and para if you will spend your time in shaded areas like forests.

=== If they are nominal 24v (commercial 72 cell) or 20v (residential 60 cell) then MPPT already has all the voltage it needs and there is no practical upside to series.   Mono v poly makes no difference here.  In this case one would likely run parallel for added shade resilience.



* this is directly related to the efficiency losses in MPPT's DC-DC conversion. Something like 5%.  So MPPT needs something like 5% greater panel voltage -- hence MPPT's greater happiness on the higher-voltage mono on nominal 12v panels.

 

[frater secessus]

Unless you have a large solar array, MPPT are not much better.

OP wants to know about Serial vs parallel with an MPPT controller.   PWM vs MPPT is off-topic for this thread.

 

[jonyjoe303]

mppt = series

mppt needs high voltage to do its magic, as long as you don't exceed 75 volts your good to go. The mppt takes the excess voltage and converts it to more amps, more amps equal your batteries get charged quicker in the limited available sunshine. The controller itself will lower the voltage to what the battery needs. 14.4 volts for most lead acid batteries.

 

[Mrcap]

I switched from 30 amp pwm running panels in parallel to 40 amp mppt with panels in series. The performance gains are substantial. I never have partial shade, flat panels on the roof. Higher voltage from the panels has less resistance but I don’t know all the reason for my increased performance but I will note that when I called and discussed it with Renogy they said with theirs and most modern panels you will see better performance connecting in series.


Sent from my iPhone using Tapatalk

 

[jimindenver]

I am in the process of setting up a MPPT vs PWM time lapse video test with each controller having its own pair of 12 volt panels. I really wanted two batteries to not only show how the PWM cripples the system early on when the battery is low but how much faster the MPPT battery comes up from the extra amps it gets. I do not know that I will have access to the gear long enough to do a series vs parallel MPPT test but common thought is that 12 volt panels may not give enough headway in voltage. Partial shading will always give the advantage to parallel, long wiring to series.

 

[Canine]

TravelMonkey, we need more information to give you a good answer specific to your unique situation. As with most things in life, context is king. How long do the wires run from the panels to the charge controller? How many panels do you have? Are they 36, 60, or 72 cell? Are all the panels the same? What is the amp rating of the charge controller? If you don't know, let us know the model number of the charge controller you are using so we can look it up. When you say "(75/15)" does that mean it can handle 75 volts and 15 amps? Different batteries have different recommendations for charge settings, so don't go by generalities there. Look at your specific battery and set up your controller for the specifications that manufacturer recommends.

Assuming your CC can handle the amps, you have only two panels, and you have a short run of wire, parallel is the best way to go. Series will be better if the panels will never be shaded or no birds will poop on them or no leaves will get stuck on them. More simply put, if you always have perfect conditions, then series is better. If one panel is not operational for whatever reason, then parallel will work better. Since the real world almost always throws things your way, parallel is better for nearly everyone.

If you have a very long run of wire, I would still hook them up in parallel, but not hook them up near the panels.; I would hook them up in parallel as close to the CC as possible.

 

[ZoNiE]

I always run parallel panels on RV's. This allows for one being shaded by, say the Air Conditioner part of the day, and then the one on the other side gets shaded by it the rest of the day. This ensures that one panel being shaded does not affect any others. I also over panel, so one does not have to worry about how the rig is parked or having to get up and angle the panels and worry about brackets not being properly tightened down for transit.

MPPT charge controllers also handle over paneling better. I also use grid-tie panels which are usually around 36-40 Volts, so I get the benefits of the MPPT controller.

My two cents.

 

[Weight]

Yep. you win. But I think I gave helpful advice and covered the OP question.

 

[John61CT]

Yes the advantages of MPPT are greatest once you get up to higher voltages on **input** from panels.

12V nominal panels are lower than optimal, only 18-22V, so putting 2-3 in series is how you increase their voltage.

Side benefit is thinner wiring.

None of which has anything to do with the voltage of the **output**, the SC's job is to convert the input, put out what V you select as best for whatever your batt mfg recommends.

Best is to buy a panel that optimizes the SC efficiency and output, also best for preventing partial shade issues.

For the 75/15 that would be a single panel with a Voc rating between 40V and 65V, and wattage up to 240W, but if you found a crazy cheap deal overpanelling up to 300W would increase average charging power.

 

[Travelmonkey]

Thank you all for replying and sorry for the delay (I was camping with no internet). Very good info and it certainly answers my questions. My trailer came pre wired with Zamp ports on roof and a very short cable run. I camp mostly in state parks so partia shading might be an issue. I think I’m good to go.