RoyS

As a final update about this issue, the daily production increased drastically after adding one additional solar panel. A few days ago the daily yield was 14.4 kWh and could have been potententially higher than that if we had increased the load in the afternoon (Graph below). Lessons learned: 1. A monitoring system like Solar Assistant is a valuable tool to check the efficiency of the system and troubleshoot problems. 2. Although inverter vendors specify an operational MPPT range in the specifications, one should target the center of this range for the best performance.

Thanks. I was worried about the fluctuations in the battery charging current shortening the life of the batteries. I need to monitor the daily yield for some time to check for improvement, as it's only been one day since I added the panel. I would be surprised of that didn't drastically improve. Edit: The yield yesterday was 10.3 kWh and the batteries were already full so I'm beginning to notice some improvement.

I have finally managed to solve the problem by adding just one more solar panel! My setup consisted of 5x 550 W TrinaSolar panels. These panels have a Voc of 37.9 V and a Vmpp of 31.6 V totaling 189.5 Voc and 158 Vmpp well within the MPPT range of the inverter (120-450 V) but for some reason it was struggling to keep a steady PV Power. I just added one 555 W panel of the same model in series so the total Voc is now 227.6 V and total Vmpp = 189.8 V. The improvement was immediate as clearly visible in the graph below.

Actually mine does and it returns "048". Is that a model number ?

With all the OEM and different versions of these Voltronic inverters, how do know exactly what you have ? Mine is labeled as VM IV and its serial number starts with SG96322 but it's red with a square LCD, not white and a round LCD like on the Voltronic website. I emailed the brochure to Voltronic sales when I first got it and the representative told me it's their 2020 special version. Today, I ran the QMN command and the result was VMIII-3600 !!!

Thank you @Coulomb for the detailed explanation!! It's a relief that the production is normal and the numbers I have are in line with your calculations (Production of the last 30 days in the attached image). I will try to experiment more with the different settings and maybe test a different inverter in the same setup. I will update this thread with the results, hoping one day they will release an updated firmware for the VM IV which solves this problem, without introducing new bugs! Cheers

My firmware version (61.02) has lots of quirks that I'm willing to live with but the mentionned behavior and low efficiency is a show stopper. I find it hard to believe that all VM IV have the same problem and tend to think I may have a defective unit that can be repaired maybe by replacing the MPPT or some defective components in it? The weird thing is that the inverter PV power doesn't fluctuate early in the morning but only after it has reached around 600-700W and the panels voltage is well within the MPPT range. What do you think ?

Hi everyone, I have a Voltronic VM IV 3.6Kw with 5x550W solar panels installed in series. I've been monitoring the PV power and trying to maximize the PV production but the PV input never seems to stablize even on a clear sunny day, stable load and charging batteries. It keeps fluctuating no matter what, and my maximum daily PV production has never exceeded 12Kwh (is this normal for a 2.75Kw system ?). I've attached some screenshots of today's inverter data which was a very sunny day. Could it be a bad MPPT charge controller ? a firmware bug ? any idea ? Thanks.