Technical Support

Before I grab a ladder and attack a PV string to inspect/fix connectors (or something else).............

For the last year since installation, I have 2 identical strings performing admirably on my roof - a string connected to each of the 2 MPPT controllers on my 5kW inverter.

Now - for the last 5 days only, suddenly I have a real mystery on my hands that just does not make sense to me (electronics background and all)

If you look at the PV graph for the day there suddenly seems to be a 600W dip in just one string's output for a period of about an hour right around mid-day (or then the highest sun elevation) .................it's as if the stupid thing forget to do its job properly.(The first day I saw it, I thought must have been cloud cover but I have been monitoring for that the last 5 days, and no - cloudless)

I thought initially it must be a funky MPPT, but swapping the strings on the MPPTs tells me the problem moves with a particular string.

It looks like this for the last 5 days - during the funky short period the string's voltage jumps and current drops by about 30%

Where in the past it used to look like this

So is this a simple MC4 acting up? (cannot understand the failing mechanism that repeatedly allows it to return to the expected quality based on A VERY SPECIFIC TIME PERIOD ONLY)

Possible a diode/panel/connection or whatever overheating since it is the absolute hottest time of the day with the max production expected in that failing period?

Shall I grab the ladder and tackle the connectors individually .............. one per day to figure out which one?

I only lose about 0.6kWh per day in total PV production (of about 19kWh) so its an irritation more than anything else because of my OCD

Any technical insight is welcome.🤔