how to wire 5 24v panels

mini4mw

New Member
I purchased 5 24v panels on sale end of last year that were a great deal. They are not made anymore, thus the good deal. Never should have bought an odd number. That being said, this is where I am now.

I have 5 24v RNG-270P panels. I was planning on setting up the panels in series and charging a 24v LiFePO4 battery bank and utilizing a 24v inverter. Max voltage and charging voltage now throwing a wrench in everything. Voc is 38.6, Isc is 9. I could run 4 panels in series/parallel and be at 80v and 18a with a 30amp MPPT, but then I'd have one panel that has no use. Too little voltage to charge the battery bank most of the time if the single panel was connecting to a stand alone MPPT. I could run 3 in series but that would put me over 100v PV input and run into more expensive MPPT chargers. Seems I'm stuck in no mans land. Run 4 panels and it fits right but waste a panel (one panel to MPPT might not have enough V to charge batteries). Run 3 panels in series and 2 panels in series, but need 1 expensive MPPT to have a limit over 100v input. If I mix a 3/2 input in series/parallel to a single MPPT, the voltage will be brought down and I'm left in the same scenario as not connecting a 5th panel.

The cost effective option is to run 4 panels in series/parallel with a 30amp MPPT and keep a spare (wasted) panel. I could use all 5 with a 3 going to one MPPT and 2 going to another if one MPPT was over 150V max input, but that would be expensive.

I'd buy another panel if I could so I could run 3/3 series/parallel.

Wondering if I've covered 'best' options or if there's something I haven't thought of. Attached solar panel output for reference as well.

Thanks-
 

Attachments

  • Solar Panel Output.jpg
    Solar Panel Output.jpg
    72.2 KB · Views: 24

snoobler

Solar Honey Badger
Welcome to the forum.

These are not 24V panels. They are 60 cell panels - more like a 20V panel. They're very popular on high series count string inverters on grid-tie. 24V panels have a Vmp of around 36V and have 72 cells.

Choices:

  1. 2S2P on ~150V capable MPPT + spare
  2. 3S2P on ~150V capable MPPT
  3. 5S on a 250V capable MPPT, midnight solar and Victron come to mind. $900+

Personally, I would get the sixth panel for 3S2P
 

MichaelK

Photon Sorcerer
You don't have to match up exactly the same model of panel. Shop around and find another 60 cell panel putting out ~31V and 8 something amps. You might waste a fraction of a volt, or a few tenths of an amp, but it's better than wasting an entire panel.

Keep in mind though for six panels, that's going to be 1620W/26V charging = 62.3A. Most likely you'll get by with a 60A controller because you really can't expect most panels to put out >90% of what they are rated at, though an 80A would still allow future expansion.
 

pollenface

Solar Addict
5 in series (192voc) + 250v mppt is the way I would go. I personally like the wiring simplicity of series configurations.
 

MichaelK

Photon Sorcerer
Keep in mind though at a Midnight250 is running about 810$ right now. The OP could get an additional panel to wire in 3S2P for a small fraction of that. Even the 250-lite is running 668$.
 

Dhasper

Solar Addict
I am using 5 60 cell panels to charge 24v lithium and am doing just fine. I have a morningstar mppt. I prefer parallel in my rv setup as having issues are likely. I have read a few times here that is Undervoltage but I am taking in the same wattage as when I used the setup on a 12 volt bank.
 

Dhasper

Solar Addict
I am using 5 60 cell panels to charge 24v lithium and am doing just fine. I have a morningstar mppt. I prefer parallel in my rv setup as having issues are likely. I have read a few times here that is Undervoltage but I am taking in the same wattage as when I used the setup on a 12 volt bank.
I meant to say as having"shading" issues.
 

sunshine

Solar Addict
Just put the spare in parallel to any of the other 4 panels in your 2x2 configuration.
Being in parallel wont change the Voc. There will only be less of a falloff in V due to the added amperage of the extra panel under load.
Remember it is V that destroys mosfets so keep Voc well below the CC limit.
 

snoobler

Solar Honey Badger
Just put the spare in parallel to any of the other 4 panels in your 2x2 configuration.
Being in parallel wont change the Voc. There will only be less of a falloff in V due to the added amperage of the extra panel under load.
Remember it is V that destroys mosfets so keep Voc well below the CC limit.

There is no arguably good reason to do this. It's literally just dead weight. It can't contribute to the array in any meaningful way unless it's parallel-mate is shaded.
 

mini4mw

New Member
Thanks for all the replies/ideas.

After all the comments, seems like buying another panel close to the same output ratings would be best. About $1/Watt and then run 3s2p (two sets of 3 panels in series, tied together in parallel is what I'm saying, I believe the abbv is correct) panels in so the volts run max ~ 93 and 18 amps and still use 8awg over 50-70' run back to MPPT. That along with 30amp MPPT may run an additional $300.
Other option would be
1) run all in series and purchase a Midnite 250v ($800)
2) run just 4 panels 2s2p and 30amp MPPT ($150)

I like the idea of Midnite's simplicity, but cost is a factor. I suppose I could also run 4 panels to start since 4 or 6 panels use same MPPT (2s2p vs 3s2p) and if I need the extra juice buy an additional panel.

Ironic, HomeDepot has the same panel sold in sets of 2.. rarely easy..
 

sunshine

Solar Addict
There is no arguably good reason to do this. It's literally just dead weight. It can't contribute to the array in any meaningful way unless it's parallel-mate is shaded.
There are only 2 panels in each string. Unlike a much longer string an extra panel in parallel to one of these series panels would make a noticeable difference at high loads.
 

snoobler

Solar Honey Badger
@sunshine

Not going to wait for the wrong answer. Here's the correct one:

1619456279114.png

The upper half of the array with the 5th panel in parallel with ONE of the other panels will NEVER see more than 8.6A. NEVER. PERIOD. The two parallel panels will ALWAYS be current-limited by the single panel with which they are in series, so the above array will ALWAYS have the same peak power as the 2S2P array, regardless of loads.

1619456518284.png

The ONLY time you will ever see a benefit is if ONE of the two panels in parallel is shaded, and the other isn't.
 

sunshine

Solar Addict
so the above array will ALWAYS have the same peak power as the 2S2P array, regardless of loads.
Your top first diagram shows 8.6 amps going through the 2 in // (edit: the original panel with the spare in //)
This should be 4.3 amps though each // pv When you have this the V across the 2 in // will rise and the V across the series will rise the same. The increase will be somewhere between Voc & Vamp depending on the PV's properties. Even though you still have the same current going through the series, it is at the slightly higher voltage. Thus wattage has increased.
 
Last edited:
Top