Different PV String Power Outputs - Problem?

[GrahamN]

Hello everyone,

New to the forums and to Solar PV systems, but I didn't do-it-myself, paid for the install. It was done 8 days ago, and I'm still trying to understand the technicalities of what's been installed and that's led me to a question on whether there's a problem with the install.

I have 12 panels (JA Solar 395W Mono MBB Percium Half-Cell All Black Short Frame MC4) installed as two strings of 6. I haven't asked, so can't be sure, but from the position of the wires coming into the roof space I have an upper string and a lower string. External picture of the setup attached. These two strings are connect to PV1 and PV2 on a Solis S5-EH1P(3-6)K-l inverter. Not sure it's relevant to the question but I also have 2 Pylon US3000C batteries as part of the system. A couple of days after the install I realized, looking at the app and portal, that there wasn't any power showing on PV2. The installer came back and replaced the DC isolator for that string.

I thought there would be some difference in power from each string but wasn't expecting it to be so much. On sunny days it appears to be a 20-40% difference, but it could just be my lack of understanding.

Roof is facing South SE and the picture was taken at 14:45 today (5 Jan), so basically no shade on the roof. Here's a screenshot of the output from PV1 and PV2 as shown in the Solis portal earlier today. Is this likely to mean there's a problem somewhere in the PV2 string? If so what sort of problem could it be?

Thanks in advance.

 

[42OhmsPA]

I bet your seeing issues from shading... Scaffolding creating shadows?
Could be a poor connection but hard to say without seeing it.

 

[Think About It]

Are you grid selling the power? The inverter will only take as much power as it can use.

But if the inverter is using all the power, it definitely seems like there's something wrong.

I have tigo optimizers on each of my panels so I can see exactly what each panel is producing. But again they will only produce as much power as the inverter can use.

I would swap the wiring from the two MPPTs on the inverter to confirm that there's definitely a problem in one of the strings.

 

[GrahamN]

Yes I'm on grid. What seems strange, is the difference is greatest during the middle of the day. Latest screenshot from today with the power to/from the grid added.

 

[Mattb4]

Looking at the difference in voltage between the two strings it does look like a shading issue. #1 string has a higher voltage and more amps versus string #2. That occurs when the panels can not maintain voltage with loading. #2 MPPT controller is maximizing what those panels produce but it can not keep up with the unshaded string #1.

 

[GrahamN]

Thanks to those that responded. Since the scaffolding was removed the strings have been much closer in output.

 

[LydMekk]

Doh!