kire

1 - yes you can add new batteries to an older pack - Lithium is generally more forgiving of things like this and via the BMS it is able to manage the charge / discharge process of the different age batteries.
2 - If you want to keep battery comms (and potentially the warranty) then you have to use the same size, so another 5.12 battery. If you are more adventurous then you can use voltage settings and mix and match as needed. Ideally if your battery is setup in a 16 vs 15 pack config then you need to keep to that pack config so that voltages match
3 - See above as well - Dyness will likely void your warranty if you don't use comms and / or add a different brand because there is no unified way to manage how different batteries and BMSs charge and discharge

I have 2 off us2000bPlus  and 2 off US2000C and i added a UP5000 to the setup
Just pick the pylontech 4 off+ batteries that have the highest DOD
So in my case i just picked US2000Plus*4+ which allows a max of 89% DOD
Anyway i dont think even if i picked US3000C which is 95% DOD the BMS of the US2000 batteries wont allow them to discharge that far
The goodwe GW5048ES can only charge max at 100amps so that is why it only goes up to 4 of batteries per pack because then it sets the max charge amps at 100 amps even if you have 20 batteries

Actually, I can't agree with that... if you are running off grid, like I am and you may have more than one cloudy day in a row, it is very useful to have more battery capacity than you can charge in a day, just to be able to keep the lights on/fridges running let me give you an example...
have 4k7Wp Solar, this can generate around 30kW app per day at the moment
have 38kW battery capacity
have 5kW inverter... we use around 20-25kW energy per day (24 hour period) just less than half of that, coming from the batteries
now, with some cloudy weather, the batteries may not get to 100% by evening and next day cloudy, again batteries may only get to 70% and down to 40% by morning, but now there's no clouds, the battery will still not get full by evening, since the other consumption also needs to be met, but that does not matter, in my case, since we hardly ever have more than 2 consecutive cloudy days.
The point is, as long as the batteries get enough charge into them, to be able to provide power for overnight without dropping too low, SoC wise, you should not need to have more capacity, just to be able to fill them up 100% during the day, like in my case, they will get there over two or three sunshine days and that is just fine. Also the charge and discharge currents when the battery is more than 7 times the inverter power level is usually hardly ever more than 0.1C, which of course means they are being treated so gingerly that they're likely to live to a *really* ripe old age.

I personally charge at max 0.2C and I also lowered my charging voltage, the combo of those two should make the batteries last quite a long time.

@kire, how do cyrylic characters get into my quote?
Almost all manufacturers limit the max charge and discharge currents to 1C. But that should only be used in extreme situation. I limit my grid charge current to 0.1C. On the other hand I set the total charging current limit very high in order to catch all the available solar power. With the actually installed PV panels there is no chance that they even reach 0.5C.

@kire,
the 100A spec is the max charging rate for each battery. I would not recommend 100A charge (per battery), that would work the battery very hard, and effect it's longevity.
If you are only charging by Solar, then the amount of kW of PV you have will determine the rate of charge (minus your loads), irrespective of your inverter's charge setting. Sometimes inverters have a separate charge setting for Grid Charging.
Depending on your needs, anything between 60 - 150 A should be sufficient. And remember, that number is the Total charge current for all 3 batteries, therefor recommendation is between 20 - 50 A per battery.

You can ad as many batteries as you like. The more the better. All you have to do is to adapt the max charging current setting.
They have to be identical in chemistry and number of cells, but may have different capacity.

Generally Yes, however there are a few conditions.

How old are the existing batteries? If they are less than two years old it should be ok.
The new battery has to be identical to the old ones. (chemistry, voltage, capacity, etc)

The old ones will charge and discharge slower than the new one, thus giving the new battery a bigger workout, but over time they should even out.

You could alternatively add some bigger panels instead of the 460's if you wanted on a separate string

So you would have 18 panels facing North?
JA 460W panels spec - 
Voltage at Max Power 42.13V Current at Max Power 10.92A  
You could connect up a 2P9S string to one MPPT +- 380V @ 21.84A is almost perfect. 
See if you have any East or West facing space to put some more panels on 🙂 
FYI I had 28 x 455W JA Solar panels on my 8Kw, only clipped on very high solar radiation days
 
 

What panels are those ? There is no limit to the amount of panels as long as you stay within the MPPT specs. It all just comes down to how you wire it , with more than 18 of those panels you will have to parallel 2 stings on one MPPT. So you will have 16 panels on one MPPT and the other MPPT will have 8 panels in one string.Oh and btw each series string has to face the same direction , so your roof will also be a determining factor.

I have 12,400W of panels connected to my Sunsynk 8kw inverter BTW 🙂 

@lavaland 10,400W is NOT a maximum amount of panels you can connect. 
10,400W is the maximum amount of DC power that the inverter will use. 
As long as ensure that the max voltage of each string is below the max of your inverter (8kw Sunsynk I assume) you are good, the MPPT will control the amperage coming from the strings to ensure that it stays below it's max. 
It is quite common to "over watt" the panels, especially in lower solar radiation countries so as to ensure good production even on overcast days. 
Keith talks about this on the Sunsynk Youtube channel.
 

Благодаря за софтуера, създаден. Усилието, което полагате, е достойно за възхищение. 👏

NOTHING exports to the grid when the grid is off. If it's night time, the inverter is using batteries to support the load, and the grid goes down then the inverter keeps on using the batteries to support the load, but will not import 1 pico amp of that power.
I don't have the technical knowledge to say HOW this is done, but it is done. It's clearly visible in the graphs that the Goodwe portal produces.

My system has a battery to charge, and it set to not export. Once the battery is charged the demand for PV is reduced to match the loads that the system is servicing at any given time.
 

Depending on the export limit setting, which is an overall setting rather than part of any operation mode. Mine is set to zero. The system never exports. This is because it doesn't make financial sense for me to export. In other parts of the world it may be worth your while. 

With my system and the situation you describe, if it can't get all the excess PV to the battery, or if SOC = 100%, the Goodwe derates the PV panels.
The last point.... I'm in South Africa, where blackouts are a daily occurrence. The system will supply the backed up loads from PV if there is enough PV. The batteries will be discharged to make up the difference. If there is no PV incoming, then the difference is equal to the load and that is what gets drawn from the battery.

Don't worry. He actually is the abc... of this world.
Any surplus of Photovoltaic Energy (DC) that is not consumed or eventually exported is lost. Every inverter only converts to AC what can be used instantly.
 

It's difficult to answer without knowing the current and VOC of the panels in question. If you exceed the MPPT current then the inverter will clip / limit to the max.
However if you exceed the voltage on the MPPT then it will blow and no warranty will fix that
So you always size the string on an MPPT to be below voltage and near max current for best performance. 

6300w is indeed the total max MPPT power of both. You can still add the 2 extra panels though. You will get better performance in cloudy conditions. You can exceed the max power input of the MPPT’s as long as the extra power is due to more current and not higher voltage. The inverter will just limit the current. Just do not exceed max voltage, that will blow it. In your case, the voltage is fine.
I currently only have 1 MPPT running on my 8kw because I am waiting for a specific size all black panel. It’s running perfectly fine. 

your answer sounds very good

Well that is what I was saying, the reality is that you cannot work in theoretical numbers only because there are always a bunch of losses. Since you aren't maxing out by a long shot (And as long as you see similar figured during the summer time) adding an additional 2 panels per string should be more than ok.

If the power of the inverter is (5 000 W. - max. input power (W)-6 500), and during the day it never exceeded 3 500 W, can solar panels be added to reach 5000 W?

No voltage has been transferred. The operating voltage range is for a string, do not add the two strings. At the moment it is and it works very correctly.

That's just how it works. PV can't provide power if there's nowhere for it to go, ie. nothing available to use it. As you noticed with the kettle, PV will provide the necessary power as soon as you need it.

Ok, so AFAIK the biggest thing with panels is making sure you stay under the MPPT max voltage. Since current is drawn, not pushed, extra current current capacity shouldn't be an issue. If anything, it may help fill in for any inefficiencies or give you a little more umph when the panels aren't getting ideal sunlight. So going from 2 strings of 8 to 2 strings of 10 shouldn't be an issue but this is all from a theoretical point of view and would advise waiting for someone with more practical experience to confirm  👍