Giel

Hi Talia
I am not sure from which inverter MPPT the drop is coming from. I could have checked it, but cannot remember.
You are 100% correct about the 4 panels being close to the inverter startup voltage of 150V. We are busy addressing this and this should be sorted soon. These 4 panels are east facing and we can add two as that is the space available on that roof.
We will also add 8 more panels on the west facing roof on MPPT2 of the master. This will then be the maximum solar capacity the roof space can handle. The total solar will then be as follows:
Master MPPT 1: now 4 panels x 425W (1700W) to increase to 6 panels x 425W (2550W)
Master MPPT 2: now 0W to increase with 8 panels x 425W (3400W)
Slave MPPT 1: now 8 panels x 425W (3400W) and will stay like so.
Total now 12 panels x 425W (5100W) to increase to 22 panels x 425W (9350W). This is potentially an overkill, but only the slave 8 panels are north facing. The master MPPT 1 panels are east facing and the master MPPT 2 panels will be west facing. So the capacity is kind of the slave MPPT 1 panels (3400W) plus either the master MPPT 1 panels or the master MPPT 2 panels or something inbetween.
Giel

Untick the charge from grid during good sunshine and do the test again. 

@razzor13bt, if I remember correctly, you have 4 strings of 2 x 480W panels. The Vmp per panel is 41.4V as per your post on 29 June. If that is correct, then you should be getting around 80V DC between PV+ and PV- per PV string. Your Imp current per string should be about 11.6A as per the specification. The total power per string is 960W and the total PV power for the 4 strings should be 3840W. My estimate is that you should be getting between 70 to 80% of this or up to 3100W. If you multiply this by an average of 5.5 sun hours per day for Gauteng, then you be producing around 17 kWh (units) per day.
If "Gnd" above means "PV-", then if you measured between PV+ and earth (at the bottom right of your orange surge arrestor in your PV combiner box as posted by you on 17 June) and again PV- (Gnd) and earth on your PV combiner box, with the panels connected, the total voltage per string seems a bit low. For instance St 1 = 22 + 14 =36V, St 2 = 21.6 +14.3 = 35.9V, St 3 = 22 +14 = 36V and St 4 = 22 + 14.1 = 36.1V. Is this correct? If it is correct, I think this is below the operating range of the King, which is 60 to 115V DC. Previously you stated that you measure around 64V using 2 x 500W panels from a friend of yours. Even that 64V is close to the lower limit of the King.
This means that either the panels are under performing or you have a wiring issue on each string. I prefer to use 6mm2 solar wire between the panels and the PV combiner to reduce losses, but using 4mm2 should be fine. The MC-4 connectors should be properly secured/mated. You can feel the connectors and the wiring to find any hot spots. If it is warm, you should investigate.
I would remove four panels from two strings and test them on the ground or if you can, connect them together on the roof, but first disconenct it from the inverters. Put these foure panels in series. It will be 1920W and should produce around 160V when conencted. be careful not to touch the wires as this can be a shocking experience. You can connect a 2kW geyser element as a load. Measure the current using a clamp on amp meter while mesuring the voltage at the same time. Mulitply the current and voltage to determine the watts. Just be careful, do this quick as that element will get very hot. If you do not get close to 1920W, then try to change the angle of the panels and make sure they face to the sun to try to increase the power. This way you can confirm whether the panels are actually producing what they should or whether they are below par.

Not always the case. It is the inverter causing this reading in the way it converts power from DC to AC. As mentioned if the inverter is disconnected from the panels this voltage goes away. I found this out while working on panel connections and could touch my + and -  with not even a tingle. As long as both are not touched. I had to work during good sun due to the time taken for the task.

On another forum, this now very dated post: https://forums.aeva.asn.au/viewtopic.php?p=60086&sid=f4ef6aab6789364dd4e6fda49c57a6f5#p60086
Take note of the comment about taking out the communications board.
I note that some of the apparent improvement in cooling isn't real; it's because the sensor for the transformer is in the cool air stream after fan direction correction. But I still believe that it's well worth doing. Otherwise, with low fan speeds, it's just enough air flow in the wrong direction to counter the natural convection effect.

geyser?

That's at 25°C. My rule of thumb is to add 7% for 0°C winter mornings; then Voc is 410.4 × 1.07 = 439 V. That's still OK, not even derating at that voltage.
That's fine. A fair bit more wiring, though. But it leaves you open to adding yet another string of 6 panels 😈
You'll also be better off in winter, when the days are shorter (less solar input) and the nights are longer (run the lights for longer).

I designed my solar system and had the following installed: 2 x Axpert MKS II 5K in parallel, 14 x 330W Canadian solar panels in 2 strings of 7 and 3 x Narada 48NPFC100. This system allows me to switch the grid off as long as the sun shines and a bit longer. Initially the installer installed the 2 strings of panels to one inverter, but I split it to have 7 panels per inverter. The system was installed early in December 2019. Everything still works fine. We are in Pretoria and generally we have more power than what we can use.
On cloudy days we do survive, but when the clouds are very low, the yield is low. I kind of figured my batteries charge to around 70% to 80% or sometimes a bit less on heavy cloudy days. I do understand this, but I am considering to add a few panels for such days.
 
The inverter spec is max 4500W, max VoC is 450V, and the MPPT range is 120V to 430V. The panel spec is 330W at Vmp of 37.2V with a VoC of 45.6V.
There are a number of options to increase solar capacity as follows:
1.    Add up to a maximum of 2 more panels for each string to increase it to 8 or 9. The power for 9 panels will be 2970W per inverter, 410.4 Voc and Vmp of 334.8.
2.    Splitting the system into 3 strings of 6 panels with one inverter having two strings and the other 1 string. The power to one inverter will be 3960W and to the other 1980W with the Vmp = 223.2V and the Voc = 273.6V.
3.    Another option is to have 4 strings of 5 panels, 2 per inverter. So each inverter will have 3300W in total and the per string Vmp = 186V and Voc = 228V.
Each option has pros and cons.
Option 1 is easy, but will need to split it anyway if I need to upgrade beyond 5940W solar. Also, to use rule of thumb safety, the Voc x 1.1 is close to the inverter Voc max for those cold winter days. The advantage of option 1 is that the MPPT minimum voltage will be met earlier in the morning and last later in the afternoon, getting perhaps a slightly longer number of hours out of it.
Option 2 is somewhere in the middle, is unbalanced, but allows for easy future expansion. A disadvantage is that one inverter will carry a higher load in terms of battery charging and might reduce its longevity.
Option 3 is a balanced system, but the Vmp is to the lower end of the MPPT range. So it will start charging later in the morning and stop charging earlier in the afternoon.
The middle of the MPPT range is at 275V. My current installation is 260.4V and sometimes shows 270V or more. With Option 1 the calculated MPPT voltage is 334.8V, with option 2 it is 223.2V and with option 3 it is 186V as mentioned above.
A)   Does anyone have experience on the “sweet spot” for this inverter in terms of MPPT range and does it matter where in the MPPT range the inverter solar input is?
   Is it a problem to have an unbalanced system where one inverter has to charge the battery more than the other? In other words, is option 2 ok?
C)   Any expansion just for the sake of cloudy days is not really worth it in terms of return on investment, but at least I will be more independent of any potential grid power failures on such days? When the system was installed in December, we had lots of rain and cloudy days and also load shedding. So those days I will be better off. Any comments?
D)   Which of the above or other options will you recommend?
E)   Any other views and suggestions are welcome.