1200W of panels in full sun = 350W output

Dan_ · January 2015

I am baffled as to what's going on to cause this

I have 2 strings of 6 Kyocera 120 panels that I just set up. The panels Ip max is around 6A (Isc is around 8A). Right now I am getting a mere 1.7A out of each string (tested with a clamp meter). Bright clear skies with full sun. Battery needs charge and charge controller is in bulk. Wiring is 12ga with CC 40ft from panels. Panels are angled approximately 40 degrees (I'm at 38 degree latitude)

These panels had a recall from Kyocera for low power output and were replaced under warranty in 2012 with remanufactured units. I'm assuming its not that issue again but I suppose its possible (??)

How else can I diagnose what is going on?

Edit: It is now 12:30pm and CC is showing ~500W now. One string measures 5.9A and the other measures 2.1A. Both strings combined are only 67v (Vmp per panel is 16.9, should be at least 100v)

inetdog · January 2015

Re: 1200W of panels in full sun = 350W output

Dan_ wrote: »

I am baffled as to what's going on to cause this

I have 2 strings of 6 Kyocera 120 panels that I just set up. The panels Ip max is around 6A (Isc is around 8A). Right now I am getting a mere 1.7A out of each string (tested with a clamp meter). Bright clear skies with full sun. Battery needs charge and charge controller is in bulk. Wiring is 12ga with CC 40ft from panels. Panels are angled approximately 40 degrees (I'm at 38 degree latitude)

These panels had a recall from Kyocera for low power output and were replaced under warranty in 2012 with remanufactured units. I'm assuming its not that issue again but I suppose its possible (??)

How else can I diagnose what is going on?

Start by looking at the output voltage of each string while it is connected to the CC.
See how it compares to the sum of the Vmp values for the panels in the string. If it is higher, then something is limiting the current. I would suggest (carefully, maybe connecting at night) putting a short circuit across each string and measuring the Isc.
If it is lower, then one or more panels is not contributing and you may have one or more low current panels with defective bypass diodes.
I would also check with each string connected by itself to the CC. If you get 3.4A, then the CC is limiting the current for some reason.
Not a full diagnostic plan, just a few things to test....

PS: The fact that the two strings give symmetric current values makes it less likely that it is a problem with an individual panel. Possibly a defective CC or a problem with the wiring from combiner to CC?

Dan_ · January 2015

Re: 1200W of panels in full sun = 350W output

It is now 12:30pm and CC is showing ~500W now. One string measures 5.9A and the other measures 2.1A. Both strings combined are only 67v (Vmp per panel is 16.9, should be at least 100v). Something is definitely up.

Thanks for the diagnostic advice, will work on getting more data

westbranch · January 2015

Re: 1200W of panels in full sun = 350W output

IS this a sudden change or gradual?
What happened right after the change out?
what was the previous best production?

biggerhammer · January 2015

Re: 1200W of panels in full sun = 350W output

I would take a VOM to each panel. One of them may be wired backwards, or broken.

Dan_ · January 2015

Re: 1200W of panels in full sun = 350W output

Its not as bad as I initially thought, made 4.2kwh today (but then again, I have so little experience here I have no way to make good judgement). Was producing 890W at 1pm. There was some very minor shading at the bottom of the panels that I corrected.

I previously had 6 panels in a single string. It typically underperformed as well, usually 400-500W at peak of the day.

So I should disconnect panel input to the CC and short circuit each panel with a meter? In sunlight or dark? The panel is good then if the reading is close to Isc, yes?

inetdog · January 2015

Re: 1200W of panels in full sun = 350W output

It should be close to Isc at full noon.

westbranch · January 2015

Re: 1200W of panels in full sun = 350W output

Do you have MC4 connections from the PV panels? If so do NOT open them under load... not designed for that...

icarus · January 2015

Re: 1200W of panels in full sun = 350W output

How re the panels wired? series, series paralell? Test each panel individually ideally isolated from e string. In simple paralell wiring, dropping a blanket over one panel should drop the string current by the same percentage that the strin has, ie 4 panels, each should drop off about 25% each. I check mine every once in a while when I think I may have a problem. A clamp on ammeter is great too to search out the answer. Under similar sun, each panel, each string should be very close in current and voltage.

On the off chance that the battery is fully charged, or the controller thinks it is (I may be incorrectly assuming a battery system?) you could load the battery greater than the total output of the PV, forcing the controller to run full out.

Good luck and keep in touch,

Tony

1200W of panels in full sun = 350W output

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