Half amperage from semi flexible solar panel? Possibly damaged?

[redpointist]

I have 3 of the 100w semi flexible Renogy solar panels, and while I was hooking them up to test them out, a gust of wind came and knocked them off platform i was setting them up on onto the ground about 4 feet below. It wasn't a big drop and the wire caught on the platform and lessened the blow a bit, but upon testing the output, two of the panels are putting out about 5A and one is putting out 2.5A.

When I connect the panel directly to a car battery in full sun (in Tennessee) its still putting out 2.5A. If I short out the two wires momentarily the amperage jumps to 5.3 amps. The volatage i measure on the panel is 19v. The battery's voltage is 13.2v. The short circuit voltage on the panel is reported as 6.2A and the open circuit voltage says its 21.7V so 5.3A and 19V seems like itd be about right for the Tennessee sun hitting the panel.

My question is why is the panel only putting out half the amperage as the other two into the battery, despite it being able to produce the full amperage when shorted?

[inetdog]

I have 3 of the 100w semi flexible Renogy solar panels, and while I was hooking them up to test them out, a gust of wind came and knocked them off platform i was setting them up on onto the ground about 4 feet below. It wasn't a big drop and the wire caught on the platform and lessened the blow a bit, but upon testing the output, two of the panels are putting out about 5A and one is putting out 2.5A.

When I connect the panel directly to a car battery in full sun (in Tennessee) its still putting out 2.5A. If I short out the two wires momentarily the amperage jumps to 5.3 amps. The volatage i measure on the panel is 19v. The battery's voltage is 13.2v. The short circuit voltage on the panel is reported as 6.2A and the open circuit voltage says its 21.7V so 5.3A and 19V seems like itd be about right for the Tennessee sun hitting the panel.

My question is why is the panel only putting out half the amperage as the other two into the battery, despite it being able to produce the full amperage when shorted?

The answer to that is fairly simple, although the details will vary with the exact panel type.

First case: The panel consists of two halves in series, each with what is called a bypass diode. This diode will conduct if you try to force more power through a cell or group of cells than it can produce based on the sunlight at the moment. That will convert an 8V section at X amps into a 0V section at Y amps to keep the forced current from overheating and damaging the deficient cell(s.)
What is happening (probably) is that one cell in the panel cracked (the panel is flexible, but the individual cells are not, past a very limited point.)
That cell can only put out 2.5A instead of 5A.
When you connect to the battery you get 16V (it appears to be a 32 cell panel if it is this one: httpDOT//www.amazon.com/Renogy-Watts-Volts-Lightweight-Monocrystalline/dp/B00IK19VF6) or less as the voltage decreases with current into the battery until you get to 2.5A. At that point drawing more current would drop the output voltage below the battery voltage and so the current cannot increase.
When you short circuit the cell the bypass diode conducts, allowing the good half of the panel to produce 5A (but with a maximum Vmp in that state of only ~8V.)

2. (Not the case with your panel) The panel consists of two halves in parallel, each divided into two sections with bypass diodes. One continues to deliver 2.5A at 12V or more while the other, damaged, half can only produce a few milliamps at that voltage. When short circuited the bypass diode in one half of the damaged half allows a total of 5A.

Basically, since you cannot get at the cells to replace or repair them, you are hosed and are stuck with a 50W panel.
This is a risk with semi-flexible panels.

[redpointist]

(it appears to be a 32 cell panel if it is this one: httpDOT//www.amazon.com/Renogy-Watts-Volts-Lightweight-Monocrystalline/dp/B00IK19VF6)

Yep! Thats the one. Thanks for the thorough response. I cant see any visible cracks in any of the cells but I guess its not likely to be visible to the naked eye, and a cracked cell seems to be the most likely scenario. Space is limited for me and I need to full output so it sounds like my only option is to buy a new one. Maybe someone on eBay with ample space will buy a 1/2 derated panel for 1/3 the price...

[inetdog]

Maybe someone on eBay with ample space will buy a 1/2 derated panel for 1/3 the price...

If it were me, I would not buy such a panel since I would worry about a small crack in one of the other cells that will grow to take out the rest of the panel. Especially since the semi-flexible design puts crack promoting stress on all of the cells.