Have been noticing this odd PV behaviour from one of my strings. At a point in the day the voltage on my MPPT goes up, current goes way down and correspondingly the production tanks as well. There is 1 string connected ot each inverter and in the images below you can see the difference between Inverter 1 (yellow) and Inverter 2 (green). Inverter 1 MPPT does not have this odd fluctuation. Panels are 335w CNBM - 8 panels per string with each string going into a 5kw Sunsynk

What could be causing this?

MPPT Voltage

MPPT Current

MPPT Power

Here's part of the graph for my system today

The app on my phone shows errors for "high DC supply" at 9:00 and 9:16. I suspect, but can't prove, that this is the east facing array. I remember noticing these after I had my PV upgraded and I was paying the system lots of attention to try to see how much difference the upgrade made. I also remember that on investigation I found entries in the error log that predated the upgrade.

Inverter is a Goodwe. I say (but can't prove) that this happens on one MPPT - the E string. Your situation seems different because you have a string supplying each inverter. Also my battery is usually charged mid morning, before the N string really gets busy, so the system generally is not pulling a lot from PV in the middle of the day and in the afternoon.

But maybe there's some helpful information for you. Now two MPPTs will be identical. Small differences in panels and wiring may push one MPPT over the edge. The E string is further from my inverter than the N string, so a tad more resistance.

20 hours ago, mzezman said:

Have been noticing this odd PV behaviour from one of my strings. At a point in the day the voltage on my MPPT goes up, current goes way down and correspondingly the production tanks as well. There is 1 string connected ot each inverter and in the images below you can see the difference between Inverter 1 (yellow) and Inverter 2 (green). Inverter 1 MPPT does not have this odd fluctuation. Panels are 335w CNBM - 8 panels per string with each string going into a 5kw Sunsynk

What could be causing this?

MPPT Voltage

MPPT Current

MPPT Power

Perhaps temporary shading from, by example a chimney. Is the drop in current at exactly the same of is it slowly moving later/earlier?

I won't be the mppt dialing anything back since it produces more current and power later in the day.