Solar string not providing optimal output

[sweasim]

Hi there, I recently got 13.kw solar system with 30x Jinko 440w panels. The panels are in 3 strings with each string having 10 panels.

String 2 consistently gives lower output (kw) than others throughout the day and I fear that it is some installation/manufacturing problem. I understand that the orientation of the 3 strings is different so their output will vary throughout the day. Please consider the following.

In morning, string3 gets the sun first and starts the production. As sun rises, the string1 and 3 get the light exposure (string 2 - green line is still in shade as it is facing west). In the evening, as only string 2 and 3 should be producing as east facing string 1 doesn't get sunlight due to slope.

Around the mid-day, all three strings should be producing at their max. BUT the graph shows that string 2 never reaches the output level of string 1 and 2. I see string 2 output curve follows string 3's curve but it the output remains much lower than string 3. That makes me wonder if there is some problem with string 2 installation or some of the panels in string 2.

Any guidance on what can cause this issue. I have notices the same on multiple days. The to-date output from string 2 is 50-60% of the other two. Any clues?

 

[HRTKD]

You may have one or more bad panels. Check out the UNI-T UT673PV Solar Panel Tester. It can tell you on a panel-by-panel basis if one is bad.

Connections can also be a problem. Check all of them. Fuses/breakers can also be the culprit.

 

[sweasim]

Thanks for responding HRTKD. First of all, do you think my suspicion is valid? The installer insists that all panels have to be working since the panels are in series. They say that this is expected behavior due to orientation. Really?

 

[HRTKD]

Orientation can factor into production, no doubt about that. One panel could have an issue that is bringing the rest of the string down. It sounds like the installer may be lazy. However, let's get into more technical details. What production numbers are you seeing. I don't think you can compare the production numbers for all strings at a single point in time. Each string will achieve maximum production at different times of the day so let's look at maximum production throughout the day, not at a single point in time.

 

[Solar Guppy]

String 2 being north east will always have the lowest harvest and looks like it is shaded in early AM as well

 

[HRTKD]

After reviewing the graph again and the site photo, I don't think you can expect string 2 to see production similar to the other two strings.

The PVWatts calculator may give you an objective answer on what to expect of each string.

 

[sweasim]

Thank you very much for replies so far. I am really trying to figure if this is an installation/equipment issue or not.
Looking at the graph, string2 never exceeds 3kw production (capacity 4.3). Shouldn't there be a 10 min window in the day when string2 will get enough/optimal sunlight to harvest 3+kw like string1 and string3 do? The curves show that even for the sun in west (after midday), string3 continue to produce comparable output to string2 (despite string 3 supposedly being in shade due to facing east and sloping away).
Again, not too much concerned about the total daily production of string. It's just why it never touches >3kw like string1 and 3 at any point in the day?

 

[HRTKD]

Compass orientation and mounting angle matter.