Parallel Solar Panels

[lmwilco1]

I have 2 Rich Solar 160W solar panels mounted flat on the roof of my Grandby connected in parallel and feeding my Renogy DCC50S charge controller. Since I ran the batteries down testing the fridge install I was watching the charge current coming in from the solar. Conditions today are sunny, and 80 degrees. I was getting 8A of charge current as measured by the Vectron battery monitor. I never did much testing when I installed the system in the camper so I decided to cover each panel in turn and measure the current to verify both were working correctly, When I covered the first panel I got 2A of charging current, when I moved the cover to the second panel I got 1.8A of charge current. I was expecting to see roughly 4A of charge current from each panel resulting in the 8A total that am measuring when both panels are uncovered.

Any idea why I only get ~2A per panel when one is covered but 8A when neither is covered?

Louis

 

[Vic Harder]

Louis, good question. First things first. If you turn off all DC loads (in the dark too) using the kill switch, so there is no charging and no draining... does the Victron read zero current flow? If not, you need to "calibrate" it... this is on the battery tab of the settings.

 

[lmwilco1]

Vic, The monitor reads fine, zero current flow with no load. Even if it was off I am not sure how that would result in my current differences. I am wondering if the solar panels have diodes in them but I thought that was standard in all panels.

 

[Vic Harder]

Vic, The monitor reads fine, zero current flow with no load. Even if it was off I am not sure how that would result in my current differences. I am wondering if the solar panels have diodes in them but I thought that was standard in all panels.

Strange. No shade at all on the uncovered panels during testing? And yes, they have diodes, which helps with partially shaded situations.

 

[lmwilco1]

There is a little bit of dirt in one corner of both panels, but I don't think that is enough to give me the impact that I am seeing.

 

[lmwilco1]

Well, it was a weird timing / testing issue. I did not shut off the loads in the camper and the fridge turned on right when I covered one panel and then the other. Today I removed he panels fro the mount and tested the current from each panel and then individually with the other covered and saw the expected charge current roughly in half. The all of a sudden it dropped to almost nothing and when I uncovered the other panel the charge went to 50% of the original charge current. I then realized that the fridge compressor had switched on which explained the difference.

Glad it was a testing issue and not a real problem.

 

[Vic Harder]

 

[LilasCook]

Hi...with most new panels having bypass diodes to shunt the current around shaded cells, don't notice much difference in power production. Now running 120 volts on one series string and 60 volts on another series string. Nice to be able to use lighter gauge wire. Mppt controllers of course. Believe most Pwm controllers are only good for panels less than 24 volts which eliminates bigger panels.

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