Quick panel configuration question

[Texas-Mark]

This will be a small stand alone system that I won't be adding any more panels to.

I have four 300 watt panels. Due to the voltage limits of my MPPT controller, my only options are 2S2P or 4P.

These are old panels. One of them produces about 16% less (40w) than the other three. I assume that if I connect them in 2S, that the lower producing one will limit the other one in that string. Is that correct?

So my question is, am I better off going 4P or will the higher voltage of the 2S configuration offset some of that 40 watts that I assuming I will lose from a good panel in series? I say 40 watts because these panels will be laying flat. So due to that and their age, I am only getting about 240 watts out of the good ones at noon, and 200 out of the "bad" one.

I'm not that concerned about more cables for 4P as I only have about 10 feet to the controller, but only having 2 sets instead of 4, of course would be better.

 

[Mattb4]

About all I would suggest is to try it with the 2S2P and see if it works OK. If you think it can do better as all parallel try that next. Panels and a SCC with MPPT do not always output what some of the models for them say they would.

 

[Texas-Mark]

I can do that, but before I go building more cables, I just wanted to know if there is any advantage to going with the 2S2P that "might" make up for any loss of "miss-matched" panels.

 

[Mattb4]

You could try 2P2S. If nothing else it gives you a third option.

 

[Texas-Mark]

Would that not give the same results as 2S2P? The "bad" panel will still ultimately be in series with good ones, and thus limiting the string??

 

[Mattb4]

Would that not give the same results as 2S2P? The "bad" panel will still ultimately be in series with good ones, and thus limiting the string??

Being in parallel with a good one might prevent the string being weaker than if it was in series with a good one. I say might because from me testing various types of panel setups with different SCC's that what works best varies.

 

[robbob2112]

Ok, so learning question for me - in this case the panel is weaker because it has something aging in the PV cells that are all connected.

Are there diodes to check when using old panels?
What is the Isc for the failing panel? what is the voltage of the panel open
Assuming you run 2S with this as one panel what current does it put out compaired to a 2S set of the good panels?

Same question in 2P? In this case I would assume the failing panel has less voltage?

My point is would a panel like that limit anything it the current is just flowing in the runs that the PV cells connect to? The silver runs connecting the panels together is intact I presume?

I searched around - I get it now, but am still curious what the readings are

 

[Texas-Mark]

What is the Isc for the failing panel? what is the voltage of the panel open
Assuming you run 2S with this as one panel what current does it put out compaired to a 2S set of the good panels?

I can sort of answer these. I have one of those handheld panel tester meters. So that is how I am seeing the output wattage. I did not really look at the actual current of each, since it gives to the actual wattage. I did test them all separably (multiple times) laying next to each other. In other words, under the same conditions for each. The voc of the panels is about 42V The bad one is about a volt lower. I could not test 2S with the tester as it goes over voltage. I think it has a max of 60V

 

[robbob2112]

I can sort of answer these. I have one of those handheld panel tester meters. So that is how I am seeing the output wattage. I did not really look at the actual current of each, since it gives to the actual wattage. I did test them all separably (multiple times) laying next to each other. In other words, under the same conditions for each. The voc of the panels is about 42V The bad one is about a volt lower. I could not test 2S with the tester as it goes over voltage. I think it has a max of 60V

I get it, no clamp amp meter.

Just idle thought - if you inspect the panel is there any sign of damage to any of the cells? And another idle thought - if someone buys 30 panles and finds 5 are not outputing the right voltage is it possible to move cells from on panel to fix the others? i.e. donate cells from 1 and replace cells on the other 4?

 

[Texas-Mark]

Just idle thought - if you inspect the panel is there any sign of damage to any of the cells?

They all have a little damage. Mostly the corner cell is cracked. The bad one has a "burn spot" on one cell more toward the middle. So yeah, it has some physical damage too besides just age.