JacquesStrydom

I guess the final answer depends on if your firmware will allow operating to 21.4A. As user reported here for Deye it is more like 20A.

Just to confirm:
The Deye 8k has 2 MPPT controllers.
You have connected the solar panels as follows:
MPPT1: 8s+8s x 460W NE = 7360W MPPT2: 8s x 460W NW = 3680W The reason I'm asking is I'm considering adding an additional string to my Sunsynk 8k.
Now:
MPPT1: 8s x 400W N = 3200W MPPT2: 8s x 400W N = 3200W Proposed:
MPPT1: 8s+8s x 400W N = 6400W MPPT2: 8s x 400W E = 3200W Sorry, not trying to go off-topic, but I think many are interested in adding more strings.
Thanks in advance.

I have also ask Deye for clarification on this issue again this morning as their previous response 2 years ago that the mppt's are clipped at 20A for safety reasons might have to do with temp rise on constant 10kw output. As @Sc00bsgraphs indicate spikes well above 10kw but constant output of closer to 9kw as i have also observed. Below response from Deye 2 years ago. Let see what response i get back from Deye.

I ramped up essential load to about 7.5kw to make space for power import  while testing - that was why the battery amps  reduced.   I would have liked to have say 7kw on inverter and 3.4kw on battery if needed.  Had a few cases where I charged at close to 7kw. (3 x 5.12kw battery bank)

Thanks for the useful Update @TaliaB. 👍

I have seen this on various occasions on the Sunsynk and Deye 8kw that the total output power between the 2 mppt's will not exceed 9000w. It will adjust the mpp so the current between the combined mppt's do not exceed 9kw. I know the sticker and the manual states 22A+22A 10400W but in reality the sum of the 2 mppt's will not exceed 9000w. 
I also had conformation from Deye that this is indeed the case. They send me an e-mail after i enquired about this 2 years ago (wording not very technical) but nevertheless conformation max pv power for the 8kw SS &Deye inverters 9000w pv output. 
 

Then it is perfectly legal and COC was rightfully issued by 1st electrician then i don't see why the electrician want to issue a new COC he just need to issue a  supplementary certificate for the added string. The cost of a new coc is going to be more than a supplementary certificate that is maybe the motivation. 

Running to 10% instead of 22% will give you an extra 1.8kwh of power 
 

What is your peak current draw from the battery? If you are hitting close to 7 or 8kW during peak periods you could set the power limit to for argument's sake 4-5kW at night. This might help to compensate for a deeper discharge, if you treat it more like a 0.25C battery. Basically, you're going to run out of power overnight anyway, may as well do it slowly and go easy on your batteries.

Another sneaky one that could get you is lighting. If you don't already have LED lights everywhere, then switching to LED lights could reduce your nighttime consumption significantly. When we moved into our current home, the previous owners had put in 100W halogen lights all over for some reason. The first thing I did was replace them with LEDs.

@JacquesStrydom Agree 100% with @GreenFields  , I had 28 x  455W (12.7kw) panels on my 8kw Sunsynk, the inverter throttles production to the max so will not go over the 10400W max DC production and 8000W AC. 
Over watting the inverter is great for low solar radiation days. 
If you still need more power you could considering adding a grid-tie to the Aux port, is on top of the 8000W AC limit and is to a max of 4kw I think.

Great stuff, ordered 8 of these and had it installed on Friday for total installed capacity of 10.9kw.   Currently peaking at 8.6kw.  I limited my inverter Solar intake at 10.38kw to match the 10.4kw nameplate spec should it ever get there. 

Those aren't max limits, those are operating limits. You can put as many panels as you like to, as long as you remain below the voltage limit of the MPPT, and below the Isc rating (I think 34A per MPPT for this inverter).

See if you can get this panel from Herholdts:
JAM72S20 445-470 MR 35边框 (herholdts.co.za)
JA Solar (herholdts.co.za)
The specs are much closer to your original panel, and I think the pricing is reasonable. Pmax=460W, Vmp=42.13V. Imp=10.92A, Voc=50.01V, Isc=11.45A
That gives you some better confidence to be able to mix strings if you must, but still try to keep one type of panel on one MPPT in a balanced number of panels in parallel pointed in one direction if you can. 
It's not a problem if Isc exceeds your maximum operating current. The Isc limit is much higher for that inverter.
 

Yes, which can be challenge to convince some installers that  is should not be inside inverter but upstream of  non essentials.

In that scenario it will pull from the grid.
If there is no grid then there are no non-essentials present to the inverter
For you to get the most from the system in a split Essential and Non Essential setup that CT needs to be moved to the DB on the incoming Eskom line pointing towards the house load. Anything between CT and the inverter will then be Non-Essential and everything after inverter will be Essential