Mixing solar panels with different amps

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gkb2016

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I recently made the mistake of buying a 175w solar panel (roughly 9.6 amps iirc) and found out when you mix panels with different output amps, the higher amp panel is limited to the output of the lowest amp panel. My other 3 panels are 100w and about 5 amps.

I am trying to get some clarification on this.

Does it mean the 175w panel can never output over 5 amps?

Or does it mean that if the 175w panel is in full sun, and the other panels are shaded, that it can pick up the slack and output it’s whole 9.6 amps (but it gets divided up between the other panels since they’re shaded) thereby making the amperage in the system 9.6a / 4 panels = 2.4a?
 
As long as the panel voltages are about the same (usually around 21 or 22 volts) AND they are wired in parallel, it will work fine, assuming your solar charge controller can handle the additional amps.

One of my systems has a 100 watt fixed panel in parallel with a portable 150 watt panel. Works great.

But...you should not add the higher power panel into a string of lower power panels that are wired in series.
 
As long as the panel voltages are about the same (usually around 21 or 22 volts) AND they are wired in parallel, it will work fine, assuming your solar charge controller can handle the additional amps.

One of my systems has a 100 watt fixed panel in parallel with a portable 150 watt panel. Works great.

But...you should not add the higher power panel into a string of lower power panels that are wired in series.

I do have them wired in series.

Everything seems to be working fine and the extra 175w panel seems to be at least matching my 3 100w panels but not putting out the full 175w (which lines up with what I had read).

Is there some other reason I shouldn't do this besides the 175w panel output being reduced?
 
If you are willing to accept the lower output from that one panel, then it might work OK for you.

It would not be a recommended practice however.
 
If you are willing to accept the lower output from that one panel, then it might work OK for you.

It would not be a recommended practice however.

I am planning on upgrading the rest to 175w now. It's going to be a tight fit (with some slight overhang lol). The 175w panel is mounted to my hood :D

That still leaves my original question, if the 3 100w (5a) panels are shaded and the 175w panel is in full sun - is the 175w panel still limited to 5a - or does the fact the 100w panels are shaded mean there is room in the system so now the 175w panel can utilize it's full 9.6a?
 
The answer is, maybe.

Normally, in a series wiring configuration, if one or more panels are shaded, the entire output will drop, even more than the one panel. But, some panels (maybe yours) will have bypass diodes and wont pull down the output from the panels that still have full sun.

Panels wired in parallel tend to have better partial shade tolerance, overall.

Again, if you want maximum output from your series system, best practice is to have matched panels. If you deviate from that configuration, you should expect lesser performance.

If someone on the forum has experimented with mismatched solar panels in a series configuration and performed actual tests and measured the output in all variations of full and partial shade on all the panels, maybe they will chime in with some information for you.

And if you can report back with your own findings, we might all benefit from this.

Good luck.
 
Last edited:
The answer is, maybe.

Normally, in a series wiring configuration, if one or more panels are shaded, the entire output will drop, even more than the one panel. But, some panels (maybe yours) will have bypass diodes and wont pull down the output from the panels that still have full sun.

Panels wired in parallel tend to have better partial shade tolerance, overall.

Again, if you want maximum output from your series system, best practice is to have matched panels. If you deviate from that configuration, you should expect lesser performance.

If someone on the forum has experimented with mismatched solar panels in a series configuration and performed actual tests and measured the output in all variations of full and partial shade on all the panels, maybe they will chime in with some information for you.

And if you can report back with your own findings, we might all benefit from this.

Good luck.

Thanks, the 3 on my roof do have bypass diodes. They are Renogy 100w.

The one on my hood is a flexible Renogy 175w. The spec sheet says it has 2 diodes but doesn’t say “bypass diode” so not sure if that’s the same.
 
I am a hybrid of experienced and still something of a newbie when it comes to solar. This is my understanding of it. The panels that are strung together must be the same, in amps and in voltage. But each "like" grouping that you have, can then be connected to a hub... that serves to merge these differing groupings and not lose the power for the higher amperages... and that hub then connects into your charge controller... which connects to your batteries.

If you connect the whole mess together, then yes, you are limited to the power of your weakest panels.
 
Panels connected in series:
- Voltages add, amperage is constant (i.e. amps delivered are determined by the lowest rated panel)
Panels connected in parallel:
- Amps add, voltages held to lowest rated panel (could damage lower rated panel).
 
…parallel:
- Amps add, voltages held to lowest rated panel (could damage lower rated panel).
If the PV is not close to ~20v, it might be defective. Must of mine—several iterations now with different wattages—have tested between 18 and 20 volts with a multimeter. I once had a 100w flexible PV (in a 3x100w parallel array) that tested < 5v. I think it was a bad connector because it did not effect the remaining PVs ability to charge, just the rate of charge. I just unplugged the failed panel (something you JUST can’t do in series without rewiring the array). There was no outward sign the PV was bad—no burning or discoloration—and it took awhile to notice that I wasn’t getting full amps at “noon”. It being my first build, I didn’t know that I needed inline fuses. So, good thing the PV wasn’t shorted. Rookie mistake.

My latest solar build uses 3 x 175w PVs in…parallel. I wanted to do series, but I had a space constraint that limited my charge controller selection. Wiring PVs in parallel is a cable cluster. And the PV wire should be bigger and, consequently, more expensive. I used 8 ga. And then there are the inline fuses needed for a 2+ PV parallel array, which makes it even more of a cluster. Obviously, series is way easier to wire, and 12 ga. PV wire should be adequate for most mobile applications. Then there’s the improvement in the PV panels, that makes partial shading much less impactful on a series array. It’s the way to go, everything else being equal.

As for mixing different capacity PVs in a series array, I don’t think I would do that, even if I got a good deal on a mismatched PV. If that was done with batteries (and, I know that batteries are different) the higher capacity battery would never be fully charged and be degraded over time (perhaps that is no longer true with modern BMS controlled batteries, but I still wouldn’t try it). I don’t know what happens in a series PV array, but it would bug me until I could swap out the mismatched PV with a matching one, knowing that matching nominal wattage is a specification for series PV arrays! These are the kind of things I think about before falling asleep at night, things I need to fix, if only for my peace of mind.
 
It's my understanding that if you have different watt/volts panels you would use a separate charge controller. As long as both controllers are set to charge the batteries at the same rate you'll be fine. Otherwise as you are finding, that 175w panel is only a 100w panel now.
 

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