And thanks for the consideration.
Was this an upgrade to more powerful panels, or have you always had those?
There is no way of getting 6400W on one MPPT while following the other limitations. Just 550Vx11A is 6050W, but no PV panel works like that, if the open circuit voltage is 550V, you wonāt see more than 80% of that often under load.
So you can add as many panels as you want as long as you stay within the max voltage and max current range for each MPPT. The actual max current is 13.8A, of which only 11A will be usable. That is the max panel Isc that is allowable. I have a couple running with 14.1A panels for a number of years now. The 6500W is also only the maximum that it can convert - but only 4600W per output (where an output means to AC or to battery). You can overpanel more than that - I have one that is running with 18x550W panels.
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Yes, it could be, except in this case, tinuva excluded that possibility by stating:
That is what I referred to earlier. Very few of the new >500Wp panels make just 11A. They tend to be around the 13A mark. For example the JA Solar panels I put up a little over a year ago make just over 13A at Imp (current, max power). If the inverter can handle 13.8A, then youāre within spec for not blowing it up, but since it will only actually run at 11A, youāre losing a good 90W per panel (2A at roughly 45V, where your typical Vmp tends to be) because of that.
I have the exact same issue. I shoved 4 of those JA Solars on an old Solis that has a lower usable max. My old ABB inverter is the exact same, limited to 11A. None of the new panels work on my old inverters 
Edit: I have to add though, youāre losing that 90W only a few hours per day, at peak afternoon sunshine. It might not be too big a deal.
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When itās a clear sunny day then the current panels are quite adequate. I understand that new panels with more oomph might get throttled by the MPPTs in the middle of a bright sunny day, but what Iām hoping for is better production in overcast conditions.
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Upgrade to add 6 panels in a new string. The other string that works well was from day 1.
Well I just had a meeting with a guy who says any job is a job and heāll just do the panelling for me. Though he made some extra suggestions
- Fuse both conductors on the PV strings (currently only the + has a fuse). Also and similarly double up on the DC SPDs.
- No East facing panels, move them to face West (says production is better in the winter)
- Or take the 6 panels coming off of the North facing roof and double up the East facing array
- He strongly recommends I double up on battery.
But those are all options. He will quote me on replacing the North facing panels, and separately on (1) to (3).
He knows Goodwe well. Says the first system he ever installed was a Goodwe ES. I said, well thatās nice, but Iām not expecting you to do anything with the inverter. He said well he could misconnect something, but in any case he is going to take photos of what he does and give me a guarantee detailing what he has done.
Doesnāt want the old panels. Thinks Iāll get something for them, but not much. Which is why he recommended (3).
Says he has picked up a lot of work from people like me who have PV and need some changes, and from people whose installer vanishes half way through the job.
We checked my roof. There is limited North facing roof, which I knew. There is not space for two West facing strings. But plenty of East facing roof.
Yes. I just checked the drawing that was submitted as part of the registration. It gives the number, make and model number of the panels. It also shows all the fuses, SPDs, breakers on the PV strings. And it shows one side of each string is earthed - so maybe we donāt want fuses on both sides of the string.
That doesnāt seem right for your inverter - can you upload the drawing again?
I only have the diagram as a PDF. Because Iām in IT and care about disk space and because the diagram was already uploaded here, Iāll just give a link to it (it doesnāt display in the post for the original upload)
https://energytalk.co.za/uploads/short-url/6tpb5mivuPBIkcSpEsorEopcwKz.pdf
Yes, that diagram only indicates the frames are grounded, as well as the SPD earth.
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Just noticed that your PV string is using 4mm cable but you have 32A fuses per string. Pretty sure thatās too high a fuse rating for 4mm cable.
The limit for 4mm^2 is usually around 30A. Sometimes slightly less for twin-and-earth/Surfix wiring because the two conductors are in close proximity. So yes, perhaps a bit borderline, but not overly so?
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So I ended up not far away from your setup.
String 1 (East facing) is 10x 325
String 2( North) is 5x 585
And the yesterday, which was sunny, the inverter was much more inclined to draw from string 1 than from string 2. When there was a big demand it would start pulling from string 2.
I tested this yesterday at midday. The load was < 1kW, and all of that was from string 1. Then 12:00 the heat pump switches on and the inverter starts drawing from 2 as well. So I then rush into the kitchen and turned the kettle on and then the inverter starts drawing a lot from both strings.
I donāt know what the software on the inverter does, but my guess would be that it inclines towards higher voltage.
The test would be to convert string 1 to the 585s. But itās not that important for me. It will use both strings when it needs to. It was drawing from both in the morning when it had to charge the battery. I saw 4kW at 9:00. Iāve never before seen that kind of power at that time of the morning.
Today is the test: Gloomy weather. Will I get some kind of improvement?
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I am getting more power than I usually would. Not a lot, but more. And the inverter is drawing from both strings.
Let me know how the battery charging goes. Sounds like your inverter behaves very similar to how mine does.
When I had a laser printer turned on, it basically killed my battery charging on this setup. My work around as you know, is configure the inverter to push 100w to the grid and that printer mostly turned off.
The charging goes well on a sunny day. I was drawing vert close to 4kW at 9:00 with both strings in use. The system was given a rating of 4kW at install time, but Iāve never seen that until yesterday.
When thereās sun and loads are low the inverter does spend more time with the 10x 325 string. Iām guessing thatās because it goes for voltage. But if I increase the load then it starts talking to both strings.
So not like it was a week ago, but if it gets the job done then thatās OK by me.
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So today, overcast morning and Iām satisfied because Iām definitely getting more power in those conditions than I used to.
Then the sun shine starts. At 13:05 Iām getting
N facing string 245.5v 0.8A
E facing string 398V 3.5 A
So I turn off the E facing string using the circuit breaker. Straight away it starts pulling 5 A from the N facing string.
Turn the E facing string back on, and straight away it drops off on the N facing string, even though just seconds ago it was able to pull 5A.
But can I trust the app? I turned off the breaker and then pulled the fuses for good measure. Now there is NO connection between the inverter and that string, but a minute and a half later it tells me itās getting 110V at 0A. I believe the 0A, but the 110V?
What is this app actually reporting?
Just now, 15:15 I put the kettle on. The house was ticking over at about 250W. The E facing string was about 400V and a fraction of an amp. The N facing was 250V and the inverter wasnāt taking anything. Demand shoots up to 1400W and it nearly all came from the N string. Now 250V at 5.4 A whilst the little bit left over came from the E facing string.
So it tends to go for voltage, which in my case means the E string. But it can pull from that N string when it has to.
This makes sense.
So there are advantages to having identical panels on each string.