Troubleshooting low power output for panels while shaded. What could be the cause(s)

Herb

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Apr 10, 2020
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Even though the house is facing South, the 8 x 100 watts panels are not producing that much power early morning and late afternoons. During winter months the output was around 500-700 watts most sunny days. The average daily power output hovered around 3.5-4 kW daily. Now that the summer is coming and the sun is higher I noticed 2-3 panes are getting partially shaded in the early mornings and late afternoons and the power is dropping dramatically to 120-150, why is there such a high drop? There are 2 arrays of 4 panels each in series/parallel going to a Victron charge controller, shading happens on 2-3 panels on the top array closer to the house (back porch) facing south early mornings and late afternoons so at least 5 panels are not shaded . I could move the panels but they are pretty much out of the way where they are. Shouldn't the output be higher, maybe around 300-400? I can understand that the sun movement during the day will affect output but I don't think it should be so low while 5 panels are getting full sun light, the shading is partial I would guesstimate 15% on each panel. Could the shaded panels be bringing the output that low?
 
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upnorthandpersonal

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The minute you have even partial shading, your panel's output will drop dramatically. If you have a series string of panels, you will notice a big drop in power. Now, normally you have bypass diodes that should alleviate some of this. What brand of panels are they and did you check if the diodes are still good? Also, how are the panels configured: all in series or do you have multiple parallel strings?
 

Herb

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Joined
Apr 10, 2020
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The minute you have even partial shading, your panel's output will drop dramatically. If you have a series string of panels, you will notice a big drop in power. Now, normally you have bypass diodes that should alleviate some of this. What brand of panels are they and did you check if the diodes are still good? Also, how are the panels configured: all in series or do you have multiple parallel strings?
Thanks for the reply, I just edited the post, but they are configured in 2 arrays 4 panels each in series parallel. The panels are Renogy 100 watts. I did check the diodes initially but haven't lately. This setup goes to a Victron CC and then charges a 5 kW LiOn power-wall I built for emergencies. I do have an Enphase PV system for the house daily use. I have considered rewiring the arrays to maybe reduce the power lost. But having trouble trying to visualize that setup, maybe 4 arrays of 2 panels each going into 2 series? The charge controller is a Victron 150/35 and the battery voltage is 36 volts, I need at least 42 volts to charge the batteries. Sorry for the rant but I'm trying to learn as I go.
 
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DThames

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Nov 22, 2019
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If you have shading on one panel of each string, you would expect a huge drop in output. You can get some cardboard and do experiments during full sun and learn a lot.
 

Herb

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Apr 10, 2020
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Thanks for the info. The shading (15%) of each of the panels in 2-3 panels (same series) array and it depends of the time of the day as the sun moves the shading changes until is gone for most of the day, the output goes back to normal and then the same thing happens later on again.
 
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