Zeo786

Sunsynk 12kW can do 100% unbalanced, or perhaps it should be 200% unbalanced, because it can do up 6kW in one phase, as long as the total is below 12kW.

If there's one system serving three dwellings, then it is possible that one person/family could drain the system more than the others do. So, for example, tenant A is being frugal. tenant B is using the oven all night long and doing some bitcoin mining on the side, and since everybody is connected to the same battery, tenant B will consume battery power to the detriment of tenant A and the main household. 

So there's your answer really.

The systems for the cottages need not be as big as the system for the main house, and you should be clear with the tenants about what is being backed up and that they have to manage the load. Inverters are current limited on the output side, and if they exceed that limit then the system will trip. So plugging in hot plates (for example) is not a good idea.
 

Just look long and hard at your pricing if you're supplying tenants electricity through battery backup. Make sure your tariffs reflect the cost of storage per kWh over the life of the batteries. Their time of use could make or break the financial viability of your system. Personal thinking would have been to give each sub-unit its own off-grid battery inverter and changeover after the meter, eg. a 3kVA 24V for essentials, and give them each the option to add backup batteries at their own expense.

You need a few of these, will solve all your metering needs and you would not need to pay third parties for tokens or use.
This stackable power meter realizes smart management with overload protection, metadata monitoring and electricity statistics.

This is the way. An inverter is not the best device for measuring.

You should be able to use sub-meters for the rentals.

Here is an older thread on the forum where you can gather some useful information.
 

BYD is one of the largest manufacturers of lithium cells in the world, and they make very high quality and innovative batteries, which is of course reflected in the price. Do you have a model name / number? 
Both Hubble AM series and some Sunsynks use BYD cells in their batteries.

I don't know if I would connect to Eskom straight away. I think that I would keep it as a back up plan. 
R100k buys a lot of diesel!
If you are going to go gas for your water heaters and stoves, those are  major users of power, apart from the pool and the borehole (my suggestion, buy an extra water tank so you only have top pump when there is sun) I really do not think that you will be using the generator very often of you have 30kr/hr of storage. 
Again, once you have the system installed and running you will have a much better idea of were your system needs some boosting. 
One thing, are the comms on the batteries you were looking at compatible with the Sunsynk inverters? 

Zeo786 you have been given a lot of spot on replies on a lot of pointers.
Some questions were perhaps not answered. If being off grid a generator will be essential even if it cost quite a bit to run. R8-R10 an hour but hopefully not too many sessions per year. 
I looked at your 29 x 545W panels. For JHB this should give you at maximum if you use of ALL the PV that you can get an average of the load of 50kwh per day. In summer you might get a maximum of 63kwh per day. The real problem why you will need a genny is that your day time load is 25kwh a day so you will have a lot of wasted PV. Storage for those bad days and specially when you have 3-5 days of rain. You will find on some days if you have discharged your batteries by 80% that you might only recharge then by 20% of what you used. 
Some bad days you might get as little as 10-15% of the summer 63kwh a day. This is where the genny comes into play. On 16 Apl we got a maximum of 5% and 3,9,10 and 17 Apl about 15% of the daily average. Refer to the graph below. Thus you might only get 3kwh which gives a major short fall and no battery charging will take place as you are going to use it all for scaled down load. These calcs are based on a annual 4kwh/kw of panels providing maximum PV facing north. In your case your daily maximum will be less due to your orientation of panels. Summer yield an average of 5kwh/kw of panels installed.
If you can switch some of your 750/750kwh load split between sun period vs no sun it will limit the use of a genny. If you moved the load to be 1000kwh during the day per month and 500kwh after sunset you will still need R100 000 for batteries. Sorry to be the bearer of bad news but being off grid when you have a daily use of 50kwh becomes very expensive.
Stats for April.

 
 

Doesn't really have to be that high, I have a 20,000ltr tank that is sitting on the ground. Water level is about 3mtr above ground level when full and that is sufficient to fill toilets etc, not enough to have a shower though. 3mtr height is 0.3bar pressure (I love the metric system)🙂  
Something like this should do the job as a pressure pump
https://www.builders.co.za/Water-Storage-%26-Filtration/Water-Tank-Pumps/JoJo-Tanks-Variable-Speed-Booster-Pump-(0-75kW)/p/000000000000716601?gclid=Cj0KCQjw37iTBhCWARIsACBt1Ixo5YMpBSaEMiZlEuXSSJl5aaDIhws4iCmBLDDYKyrhSpqNvICxQwMaAkdnEALw_wcB

I am also in Johannesburg, Midrand. 
Regarding over watting you inverter, you will loose the extra power on those high production level days, but will make extra power on the lower days. 
When you get your pressure pump, make sure it is one with a VSD (Variable Speed Drive), you set the desired pressure and it will only drive the motor as fast as it needs to go to keep the pressure.  They also do not generally require a lot of power to start the motor as they have a soft start but if you have a leaky water system they tend to switch on/off quite a bit. Mine uses about 2kw/hr a day but suspect that it is not an optimum setup and it gets switched off at night after 10 and we just use gravity feed. 

I am not an electrician so you would need clarification from a qualified person at what the options are but the way my system works is. 
All power comes in to my property through my Main DB Board. It runs earth leakage for my house and has 40A breaker switches for Sub-DB-Boards at my pool stables and cottage. The Stables and Cottage each have their own earth leakages on their sub-db-boards. 
I monitor the power going to through 16 circuits on my main DB Board which includes the power going to the sub-db boards. 
I have a disk meter for power going to my cottage which I bill my tenant for. I take a picture of the reading at the beginning of each month and minus that from the next months reading to get the monthly usage.  
Only 3 phase item I have is my water pressure booster pump that is on a VSD that runs of single phase.
Borehole pumps can be 3 phase as well which are usually better for solar but I have a 2kw single phase running of my 8kw Sunsynk without any issues (I do have grid backup though).
Fusion is through a different local supplier I think. DEYE is essentially the same as Sunsynk just different software, I would go with the Sunsynk though, support is very good and the price difference is usually negligible. 
Generator Running costs - 
Macafrica 5kw generator - 
https://www.adendorff.co.za/product/mac-afric-6-5-kva-5-kw-standby-enclosed-type-diesel-generator-220v-single-phase/ 
Quotes the fuel usage @ Fuel consumption – 1.67 l/ph @ full load
At a ruff calculation  say the generator is using 1.5ltr/hr  @ R23/ltr  = +-R35/hr  @ 3.5kw load = R10/KWh for diesel power (should be a pretty safe number) 
Regarding production and taking into account the really bad conditions we have had recently for solar. These are my figures for the last month:

If you have the system in place and finding that you need to run the generator more often than you want o it will be relatively easy to do the numbers and work out whether it it is better to add more batteries or more panels . Until you actually know what your requirement is though it is very difficult to predict. 
It sounds like your two main users of power will be your borehole and your pool.  I use the solar forecasting in Home Assistant to automatically decide whether to switch the pool on for the day or not. If it is going to be overcast the pool doesn't switch on.  The borehole also doesn't usually need to switch on every day so if you build in some intelligence into your tank level monitoring you could automate that so you are not pumping when using your battery power but will pump before you run out of water. Are you going to have a pressure pump or are you going to use a tank stand? 
Other thing to consider is your panel layout, an East/West split would probably be best. Gives you good power in the mornings and evenings and over a longer period than a pure north facing array(although slightly less power altogether) . You can also overwatt the panels, the max solar power the 8kw Sunsynk will produce is 10kw but I have 12kw of panels on my system in an East/ West Split as an example.   
 
 
 

I would say on average I get 2-5 days a month where it rains the whole day. It feels longer but here are the graphs to prove that it only feels longer.
January to April. I have a 10kwh battery that is discharged at 80% depth of discharge. So on most days where noone is at home or no washing is done the house will only use 12-15kwh.
 

Hi @Zeo786
 
I 100% agree with what @iiznh & @Calvin said.  I would definitely suggest going with a larger single phase if possible, makes more sense as you don't have to worry about getting the phases balanced to maximise your power as the 3 phase inverters are mostly in effect 3 x smaller single phase inverters running in sync to generate a 3 phase signal.  You can run 3 phase devices of a single phase power supply if you use a VSD btw. 
I woudl also suggest that it is a better plan to consolidate & centralise you power as much as possible, I would not have separate solar installs for the borehole & pool and would just manage them centrally. I would also not have separate installs at the cottages. 
As @Sidewinder suggested as well, one of the main issues you will have is controlling your heavy loads so I would definitely agree on having Smart Switches on all your heavy loads, e.g. Pool pump etc.
There are a few extra things that I would suggest that will not cost a lot of money but will make a big difference. 
1. Power monitoring - I would install power monitoring so you know where your power is actually going, there is nothing more frustrating in a large install than have a 4kw load and not knowing where the power is going. I have personal experience with this as one of my tenants had there oven on during load shedding, if I hadn't been able to see where the power was going I would have had to start switching circuits of on my DB Board to try and stop the bleed on my battery 🙂. Emporia Vue 2 is a pretty good option which you can buy of Amazon for about R2.5k. It will monitor 16 circuits on your DB board and they work very well. It does however use the cloud but can be converted if you have the time 
2. I would go a step further than @Sidewinder on the control side and would suggest installing Home Assistant to manage the switching off and monitoring of all the loads. Is open source so the software will not cost you anything, hardware +-R3000 for a decent platform. Main thing is that it will take you some time to work out how everything goes together, there are however lots of guides on the forum and Youtube. 
3. I would put in either DEYE or Sunsynk inverters but only because I have one and know it pretty well. I am sure that there are many other options available that would work. 
FYI - I have a grid connected 8kw Sunsynk with 2 x 6kw BSL batteries and 28 x 455W panels which generates on average 900 - 1250kw/hr per month .
I run a house, cottage, stables and staff kitchen with 4 geysers, a pool, a borehole & a pressure pump and am about 75% off-grid with most of my usage being at night once my batteries to get me through load shedding are flat. 
In regards to the big question about whether to spend to 100k and connect to Eskom or not, I would say a few things. 
- Important to remember that connecting to Eskom will not only be a connection fee but also a monthly fee. 
- Eskom is never going to get any cheaper 
 
I would view the installation as a learning process rather than a fully installed solution out of the box
I would install the 30kw/hr of batteries & the panels that you specced along with a 6.5kva diesel generator as a starting point as you can always charge the batteries with the generator if required. 
When doing the install I would get the installers to leave some space to make it easy to add in extra panels & batteries in the future if required. 
Would give the system a few months to settle down and would review the data to see where I need to add extra capacity if at all. 
Once you have the system installed it is very easy to do the numbers so you know whether it makes financial sense to add extra batteries or not. I suspect that it would make more sense to put up more panels so that you still make sufficient power on lower solar radiation days. 
Until then you will still have the generator to ensure that you do not run out of power and you can configure that to automatically switch the generator on when your batteries reach a low level. 
 
 
My monthly power production

My annual grid usage & production

 

My daily use is about 27kWh, my battery is 20kWh, I have a 20% SoC, so 16kWh usable capacity.
This works 85% of the time, the other 15% I use CoJ prepaid.
The problem is when it rains for a whole day or two or three.
To be 100% off grid, you will need a lot of batteries or a generator.