Alex Feldmann

No, there should be a max Isc rating, which you should not exceed, for the 5kW SunSynk, it is 17A.

Instead of just using a spreadsheet it helps to understand how/why the calc is required/done.
Here is a write up for the OP to figure it all out...Can't remember where I got it from and cant take credit for it.
As temp decreases, panel Voltage(V) increases. We want to calculate the maximum Voc for a panel at the minimum temp we expect in the region. So for JHB we use 0’C, in Bloemfontein we use -10C or whatever you chose...
To calculate string length (series) use the total Voc (Sum of voltages, because they are in series remember, (+) including adjustment for cold temp) from panel data sheet and then do as follows;
 Record-low temperature: -10ºC (From your region, town)
Temperature coefficient of (VOC): – (0.30) %/ºC (From data sheet *)
Module open circuit voltage (VOC): 39.4 V *
Inverter maximum input voltage: 600V (From inverter, MPPT data sheet)
The STC temperature is 25ºC. This temperature needs to be deducted from the array location’s record-low temperature of -10 degrees as follows:
25 – (-10) = 35º difference.
Multiply the 35º difference by the temperature coefficient of VOC (I’ve used the positive value for an easier calculation, though you get the same result) then multiply by the module’s VOC:
35 x 0.0030 = 0.105
0.105 x 39.4V = 4.137V (So the Voc will increase by 4.13 V if the temp goes down to -10C)
This is how many volts each pv module will increase due to record-low temperatures.
Add the voltage increase to the Module VOC.
Then divide the inverter maximum input voltage by that number. This will give you the maximum number of modules that can be wired in a series string per that inverter and specific location.
4.137 V (from calculation due to low max low temperature) + 39.4V (from datasheet) = 43.537 Vmax (At -10C) Increase in voltage due to temp drop per panel.
Normal voltage at 25C
600V / 43.537 = 13.7 Panels (round down to a whole number)
The maximum number of pv modules in this series string is 13.
A series string of 14 could potentially produce more than 600V during record-low temperatures.
When string in parallel, add Current, V stays the same, when in series, add Voltage, I stays the same.
 

I'm happy with my "centralised" system as it saves the most money and is the most versatile and required no rewiring.

I'm not off-grid or in a remote area - I'm still connected to the Grid (pre-paid so I only pay for what I use).
I'm looking to grid-feed and make some $$$, but CoJ are not being helpful.

For redundancy, in case the centralised inverter breaks, I have:
Grid as a backup. Cheap generator which I bought some years back before I got the PV+Inverter+Battery system which I can use if both Eskom and Inverter broken. Candles 🙂 For those that are having issues with their cheap generators not syncing, I highly recommend a low technology 4 way manual bypass switch:
Normal Operations (Grid -> Inverter -> House) Grid Direct (Grid -> House) [ used if inverter breaks ] Generator Direct (Generator -> House) [ used if inverter breaks & eskom breaks aka zombie apocalypse mode ] Off I use the the 4 way switch as it is extremely reliable and offers unprecedented levels of redundancy.
Fortunately all the equipment (Sunsynk Inverter, Batteries, panels) have good long warranties and local repair centers.
Here are some statistics for my centralised system from 21 Nov 2021 to 29 Mar 2023 (16 Months):
567 grid outages (load shedding + power fails + me messing around) - probably ~400, as any period that goes past midnight counts as an additional outage. 956 hours of darkness = 39 days and 19 hours of darkness for my neighbors but none for me Longest Grid Outages:
19h37m37s - 05 Dec 2022 - cable theft - not affected 19h01m59s - 15th Oct 2022 -  lightning took out a phase in the suburb - not affected 9h23m59s - 30th Oct 2022 - substation outage - not affected 7h50m - 2 Nov 2022 - substation outage - I was down for 3h10m In 16 Months:
Down once for 3h10m - better EAF than Eskom. Never used the generator 83.4% self Solar generated, 16.6% from grid (due to cloudy rain days) Saved over R24,000 - Will save more with Eskom's 18.65% (29.53% for urban) increase.

For longevity of LiFePo4 cells/batteries, best is to always stick to 0.2c or lower as recommended by the actual factories that manufacture them.
Many many many resources online about this.
The occasional short burst to the max the bms can handle should not be a problem, but your continuous overall loads and usage should try stay within the 0.2c range.
That way your battery will/should last long enough to easily justify the high cost.
Always remember most of the specs shown by these brand companies are for marketing purposes and mostly related to what the BMS can do, they all try to outdo each other while trying to stay within almost safe ranges.
e.g. lately the new marketing trend is to say 6000 cycles but they become vague with the rules to achieve said 6000 cycles.
At the end of the day it's the underlying cells and their specs that count, they have very specific parameters in which they work optimally and safely. No amount of marketing can bypass those.

So now let me get into the HF vs LF design difference.
Low Frequency designs work like this. You take your 48VDC, and you convert it to 48VAC at 50Hz (a little bit less really, there's some losses in this part). Then you feed this 50Hz low voltage into a big old conventional transformer and on the other side pops out 230VAC. The transformer needs to be big, because the time period t = 1/f is relatively long when f = 50Hz, so you need a nice big store of magnetic energy.
A high frequency design works similar, but it has an extra stage at the end. You again start with your 48VDC, and convert it to 48VAC... but at a MUCH higher frequency (typically 40Khz and above). This also doesn't have to be a sine wave. You then feed this into a transformer again, and convert it to a higher voltage, and then you rectify it back to DC, so that you end up with around 350VDC. This is the so-called high-voltage DC bus that we sometimes talk about, and there is a reason why it needs to be higher than the expected 230V.
You then have a final stage that takes this 350VDC and switches/slices it into a sine wave, and voila, you have 230VAC (RMS).
Because your frequency is much higher, the time constant t = 1 / f is much smaller, and hence a smaller magnetic store is needed.
Also, why 350VDC? Because the 230VAC we are used to is actually an average, an "RMS" value. It's the equivalent DC voltage if you will. Visually, you could think of taking the peaks of the sine wave, slicing them off, and dumping them into the valleys, and it will then level out at 230VDC. The peaks of the sine wave is actually around 325V... and this is why the high voltage DC bus must be at a higher voltage.
OK kids... class dismissed. If I got something wrong, there will be a teacher along to correct me shortly 🙂
 

I know I'm a bit early, but I'm not allowed to play with computers all day.

This is a great forum, full of wise and helpful people and with a marked absence of flame. 

I wish you all a great new year. May the sun never set on your solar panels.

Hello @JohanBrakpan and welcome!
This is set in the System Mode screen. Take a look at this (random) system mode screen as an example:

For the entry circled in Green, it tells the inverter that between 00H05 and 07H00, it must use 5500W of power to service essential loads from the battery until the battery SoC is at 30% (and then use Grid). The entry could also be interpreted as telling the inverter to use 5500W of PV to charge the battery (if there was PV available, but we know that no PV would be available at this time slot). For the entry circled in Red, it tells the inverter that between 11H30 and 12H30 it must use 5500W of PV to charge the battery to a 65% SoC, if the battery was lower than 65% SoC. If the the battery was over 65% SoC, then It could also be interpreted as telling the inverter to draw current from battery to supplement PV in order to service essential loads, until 65% SoC was reached. For the entry circled in Blue, it tells the inverter that between 17H00 and 18H30, if the battery is lower than 95% SoC then use 5500W of Generator power to charge the battery to 95%. Or, if the battery is higher than 95%, then use it to supplement PV to service essential loads  I hope that this helps. I have started a guide on the System Mode screen to assist people, here is version 1.2:
The inverter will use any source at its disposal to keep essentials, or "Load" alive, within constraints set regarding the battery in the System Mode screen, Work Mode 1 and 2 tabs; The whole System Mode screen revolves around the battery: The inverter will draw from, or charge battery to the desired SoC, at the desired time: from PV (or Grid, or Gen if ticked, and if both ticked, then in that order) drawing from the battery, or charging the battery at the rate (W) specified in the stated power level (but not at a rate higher than what the BMS allows); If Load Priority is ticked, it will use PV at the specified rate (W) to first service essential loads; and if any PV is left over, it will use the left-over PV to charge the battery (even if the battery SoC is higher than what is set); if PV is too little, or the rate (W) set too low to service essential loads, then it will draw what it needs from Grid / Gen / Battery <exact order to be confirmed> to supplement PV; If load priority is unticked: It will use all PV to charge battery, at the specified rate (W) (and will continue to charge past the desired SoC which is set on the timer) If Grid or Gen or both is ticked, it will use Grid or Gen (or if both ticked, then in that order) to achieve the desired SoC of the battery; If the desired SoC is achieved for the timeslot, unlike PV it will stop using Grid / Gen to charge the battery. It does not like to waste PV. Note that battery charge / discharge rates in the timer are overridden by the values in the Battery Setup screen, Batt Type, Batt Charge and Shut Down tabs.

Here are my notes on the SunSynk 8k on the v7 Dec 2021 manual:
https://www.sunsynk.org/manuals

These notes are for a
SynSynk 8k PV Lithium battery Zero Export (self consumption) no generator all loads on "Critical" If you have no PV or no Lithium or are exporting, then these notes are not for you.

My use case is as follows:
During day, use solar to run house and charge the lithium battery At night, use battery until 20% then use grid At night, if no grid (load shedding), use further 10% of battery then shutdown. At night, if grid returns, charge battery to 20% First set the Lithium Battery up as per manual section 5.13 Setting Up a Lithium Battery
Note that the charge / discharge Amps in image below is at 48V.
The charge / discharge Amps in the image needs to be below the "C" rating of your battery bank.
This needs to be below the "C" rating of your battery bank.

If you have 4 batteries in parallel, the charge/discharge current (Amps) increases by 4.
I have 6.4kWp of PV and 4x100Ah 1C batteries.
I use 150A at 48V = 7200W (150A/4=37.5A) which is less than each AM2 battery Amp and "C" rating.
Initially I had an 85A charge setting, and this limited the PV to battery charge to about 4000W. 
After changing to 150A (48V) the batteries charge at ~6kW from the PV or ~1.5kW into each battery (at PV peak period).

It is highly recommended to connect the BMS to the inverter via a suitable CANbus or RS485 Modbus cable.
This allows the BMS to accurately control the charge from the inverter.
Confirm the communications is working via LI-BMS, you should see something like the left panel above.
If you get the screen on the right (just numbers), then the communications is not working.
Try updating the Inverter / battery firmware.
Support for new batteries is being added to the SunSynk firmware continuously.
The Dec 2021 Installer Manual has 43 different Lithium batteries listed.

--
Second set the Charge Amps and Tick Grid Charge as per manual section "5.11 Generator and Battery Page"
I use 60A setting which at 48V is 2880W

I have a relay that bonds neutral/earth connected to earth spikes when there is no grid.
See https://www.sunsynk.org/post/automatic-neutral-earth-bond
--
Third set the Shutdown % as per section "5.12 Battery Discharge Page"
I use shutdown 10% for a lithium battery - remember 10% is only if there is no grid and no solar (load shedding at night)
Normally the inverter will discharge the battery to the SOC/V (20%) setting in System Work Mode 1 below, then switch to grid.
The inverter will restart when 15% SoC reached (charged from 10%)


--

Fourth is System Mode - these settings are confusing as they have different rolls see Section "5.14 Program Charge / Discharge Times"
Charge / Discharge Times are designed for "Time-of-Use" functionality and grid export.
The idea behind of TOU is to load shift from peak to off-peak and export/use battery during peak and charge during off peak.
I don't use TOU or export, but these settings are required to ensure the inverter works as I want.
Since I don't do TOU, I've used the same settings for all the periods - 20% SoC & Grid Charge ticked.

I could only get the inverter to work as I expected when I ticked "Use Timer" - else it seem to work like a UPS.
I set my SOC/V to 20% and ticked "Grid" [Charge] as per image above.
Grid Charge is only dune under specific circumstances from 10% (Shutdown) to 20% (SOC/V) and is not normally used.
See "Grid Returns" below for effect of Grid Charge tick.
Note: I don't have anything on the Grid Side or Aux (Gen) Load - I do have a CT coil on the Grid side.

How it works with the above settings

Day Operation
The inverter will use Solar to power the Loads and excess to charge the battery to 100%
Once the battery reaches 100% about 11:30am, the excess is not used as I have zero export ticked.

Night Operation (or no sun) & grid available
Battery above 20%, the inverter will use the battery to power the load (note I don't have anything on the Grid side or Aux side)
Battery at 20%, the inverter will use the grid to power the load.
The battery will drain from 100% to 20% and stop and switch to grid.
The battery will remain at 20% waiting for Solar.
There will always be a 10% reserve in the event of no grid (see "No Grid" below).

No Grid (Load Shedding) at night
The inverter will use the battery from 100% to 20% then to 10% to power the load.
Battery at 10%, the inverter will shutdown.

Grid Returns (after Load Shedding) at night
IF you have "Grid" charge ticked AND Battery < 20% THEN
   The inverter will use grid to charge to 20% and stop charging the battery at 20%.
END IF
Once Solar returns, Solar will to charge the battery.
Note: Battery will hardly ever go below 20%. You need to be at 20% first when load shedding happens.

EDIT1:
One last tip - if LI-BMS is not working, ensure your inverter firmware is current as new battery support is being added all the time:
Nov 2021 Installer Manual had 28 Lithium batteries listed
Dec 2021 Installer Manual has 43 Lithium batteries listed

I found the below video on the Deye to be of some help in explaining TOU
Use pause/slow motion to see the animations.
https://youtu.be/79IUkH3tPQ8

EDIT2:
Clarity on Amp and "C" for battery bank.
EDIT3:
Clarity on the "Grid Tick" in Work Mode 1

Ok. Maybe they have changed their ways wrt sharing of firmware. 🤞The cell number that I posted supports growatt SA 

hubble_lithium_am-2_a4_pamphlet.pdf
Hi PJZ790
see attached. Up to 100A charging current

Assume Solar Module 1S
Voc = 48.2V Vmp = 39.6V Imp 9.35A
Solar Array 6P2S
x6 Strings in parallel   Vmp = 79.2     Imp = 56.1A
Solar Wire Sizing Recommended
Assume 40 meter between combiner box and Inverter
Wire size of 16mm2 is Required for <3% Volt drop @ Imp 56.1
 Wire size of 10mm2  is Required for <3% Volt drop @ Imp 45A

Recommendation would be to check if a  16mm2 solar cables (Or x3 6mm2 per phase) are installed. 
If the solar cable is not 16mm2  (Or x3 6mm2 per phase) then the solar array cannot supply the max. required power to the inverter when the load is increased, due to power losses within the cables
 
For additional info Refer to inverter manual page 9

Change <3%  to <10%

1.       Obtain battery specification first.  
        Typical spec for a 12V 200Ah lead acid gel
-         x4 12V 200Ah Lead Acid Gel Battery
-         Connection is in series thus Battery Bank = 48V 200Ah 
-         Max Battery Charge Current = 46A
-         Max Battery Constant Discharge Current = 45A
-         Battery 5 Sec Discharge Current =  1850A
-         Battery Short circuit current = 3422.5A 
2.       Obtain DC cable specifications (for 25 and 35 mm2)
-         Max continuous current rating of a 25mm2 cable = 104A
-         For a 35mm2 cables - Volt drop @45A =  351 mV
-         For 25mm2 cables - Volt drop @45A = 459 mV
-         For a 35mm2 cable the fault rating for 1 sec = 4025A
-         For a 25mm2 cable the fault rating for 1 sec = 2875A 
3.       Recommendation:      25mm2 cables will be suitable
-         Ensure Correct SCPD i.e. Fuse are selected
-         Volt drop is negligent <1%
-         Refer to battery manufacturers spec first before sizing cables
-         The 25mm2 cable is rated for 104A continuous current
Note: 
-         Only  fuses to be installed (due to its fault current limiting properties)
-         Correct Fuse selection will ensure that the prospective fault currents will be below the cable fault rating
-         Current limiting MCB are very expensive compared to fuses
-         The battery spec have been assumed  due to lack of the battery specification. 
-         DC Cables length was assumed to be 3 m Pos. + 3m Neg. Normally installation length between 1-2 meter

My Solar System_210417_092712.pdf
 
Hi @Koppies
I have a similar system as to what you are proposing / installing. See attached doc.
growatt 5kW SPF 5000 HVM WPV P
150AH 12V x4 Lead Acid Gel batteries
X12 330W poly crystalline modules 6S 2P arrangement 3960Wp

Actual Off the Grid for 2021 thus far
Jan -  Feb 2021                   7hoo - 19h00 
March - April 15 2021          8h25 - 18h00 
Note - Solar charging batteries 24/7 only
 
What I would recommend
1. Increase your modules to achieve an installed capacity of 5500Wp, if the budget allows. 
2. Install a Hubble Lithium AM-2   C rating 1C 51V 5.5kW battery x1 see attached spec
3. Depending on the roof area install 8 modules now in series 8S and in future another 8S modules in parallel to the existing modules  Thus 8S2P

I would only install within the non essential DB for this application.

Web interface sorted.  I can now remotely alter my inverter settings.
Next I want to integrate the settings into my automation flows.  This would essentially allow me to run two seperate sets of settings, Loadshedding vs No loadshedding.  The load shedding settings can be triggered by a webhook and will ensure that the battery charging is prioritized when loadshedding is active.