MPPT 150/100 low and fluctuating power output

System has been running well and as expected since commissioned about 6 weeks ago. But for the last 3 days, the MPPT 100/50 output wattage is fluctuating and the level is much lower than expected.

The last three days have been overcast but in the past 6 weeks during similar overcast conditions the system has maintained a fairly consistent 100W to 200W PV output.

System has four Longi LRS 72HPH 550W Mono panels wired in parallel to the MPPT. The MPPT is charging a Volthium LiFePO 24VDC 200ah battery that connects to a Magnum Pure Sine Wave Inverter/Charger - MS4024PAE.

Here is a sample from Victron Connect. Output wattage fluctuates randomly from near 0 W to less than 140 W. When scanning, the MPPT seems to hit 600W (in one instance) but then returns to the fluctuating output.

I would appreciate any troubleshooting tips. I have already checked the PV wiring and connections.

Thank you

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seb71 commented · Aug 25, 2023 at 06:58 PM

What was the battery voltage and what was the PV voltage?

Any loads?

Battery SOC?

"Overcast" can mean very different conditions.

When there is clear sky, do you get the expected power?

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abegweit seb71 commented · Aug 25, 2023 at 08:21 PM

Hi @Seb71 the inverter is powered on but there are no AC loads, so it is in search mode drawing less than 30W plus about 20W for the Cerbo and router. Here is a picture of graph from Victron connect showing PV (blue) and battery (orange) voltages.

Battery SOC is low just 8%, with voltage of 25.8V

I agree. overcast is ambiguous but I have a second Victron system operating with 2 km of this system. It is a similar 24V configuration with four 425W panels wired in parallel to a 100/50 MPPT. This is the output from that MPPT this morning:

And this is the output from the system in question over the same period:

These are both remote systems and I am not there today. But I can tell from the nearby system that the sky was clear for brief periods between 10:30 and 11:00am. Three peaks are visible in the second screen shot showing the system in question, but their durations are much shorter.

Thank you

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