Victron 100/20 MPPT PV power drop to zero but PV voltage normal

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fwsage asked Jan 10, '22

Victron 100/20 MPPT PV power drop to zero but PV voltage normal

I have a Victron 100/20 BlueSolar MPPT connected to a PV array (2x 35V, 360W), charging 2x 24VDC lithium batteries (PowerPlus Life Premium N70). We have a BMV-702 battery monitor and a Venus GX comms module, and use a SCADA system to monitor performance.

The load on the system is quite small (only around 0.4A max), so the batteries are usually fully charged early in the morning. At this point, PV voltage goes close to Voc (~40V) and PV power drops down to support the load current as expected. At sunset, the batteries start supplying the load. This has been installed for several months with no issues.

In the last month, we have had a few occasions where the PV power has suddenly dropped to zero, and doesn't recover for a number of days. PV voltage remains at a normal level each day, and there is no change in load current, so I can only assume there is an issue with the MPPT unit.

The customer has queried if it may be related to temperature, as there have been some 40+ deg C days recently (reaching around 50degC in the cubicle); however the MPPT is rated to 60degC, so I would have thought it should be ok. A nearby site hasn't had the same issues.

Has anyone experienced anything similar? My thoughts are that it is a faulty MPPT unit, but I'd like to rule out other causes.

MPPT Controllers

2022-01-10-08-44-33-solar-pv-power-drop-idremoved.png (247.6 KiB)

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Answer 1 · 2022-01-11T11:01:18Z

kevgermany answered · Jan 11, 2022 at 11:01 AM

In this graph (nice one!) Battery is showing 100% when charge is zero. Looks like a normal day here, perhaps I am missing something.

Is the BMS cutting the charge? Would help to see the periods from normal to no charge, then no charge to charge.

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fwsage commented · Jan 13, 2022 at 01:41 AM

Thanks for the response. I have attached a few more trend screenshots, including a normal day for comparison, the direct aftermath of when we get a failure (in this case, battery discharging until fully depleted until the system recovers a week later), and a longer term view of failures.

Normal:

Aftermath:

Longer term:

Problem day - highlighting error when PV power drops out:

Same problem, different day:

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2022-01-10-08-44-33-solar-normal-day-idremoved.png (216.2 KiB)

2022-01-13-09-39-33-vmware-horizon.png (209.6 KiB)

Answer 2 · 2022-03-26T17:57:04Z

l19 answered · Mar 26, 2022 at 05:57 PM

I have some experiences with this also on 100/20 MPPT.. But it happens only for a few tens of minutes.. then it recovers.. However firmware updated 2-3 times since your post.. Bulk battery voltage is set to 28.2V and second MPPT (150V/35A version) delivered power from west roof in that time.. You can spot the zero power from 16:20 to 16:40 aproximately.. It happens only some days (spotted maybe 3 times this year). The fluctuating voltage on battery (red) is an oil radiator converting excess power to heat needing some time to cool down, then heats up again..

1035wp-vychod-slnecno-2632022-hq2106378n4-day.png (116.8 KiB)

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