Bismuth

This is a question of personal preference. What is worth more to you? Saving money for a few months or a mostly uninterrupted way of life? If the former then do panels now, if the latter then get the battery first. After you've checked what's in the piggy bank, of course. 

Make sure that the combination of battery and inverter is good. Not all batteries get on with all inverters. First prize is what we refer to as "comms", which is a network connection between the inverter and the battery pack so that the batteries can tell the inverter what they want. 

There are other factors to consider, like charge and discharge rates of batteries. Get a handle on your monthly electricity consumption so that you can size the system appropriately. Give thought to what circuits you won't back up (a geyser, for example, can take a lot out of a battery). All the things a good installer would guide you through 😉 
 

Wow, thanks for the comprehensive answer! This is very helpful. 
It sounds like the way forward is quite feasible. 

Thanks!

OK, so you will find someone that will just install what you got. If you buy all the equipment and ask for an install most installers are happy to work with what you got, unless its an inverter they aren't familiar with and you will have to ask another. Many will DIY if they can but installers aren't completely unreasonable.
Just make sure you stay on top of that stuff yourself. Whomever you end up buying the system from will have a warranty and RMA process that you will have to handle yourself if necessary. Just make sure you get a CoC for the installation since most suppliers are going to need this for any warranty claims.
There is often additional surge protection, changeover and a sub-DB for the inverter you will need to look into. System with solar will also need a PV-DB with DC fuses and a switch, batteries also need a DC fuse. These kinds of little things will make the endeavor a little more expensive...
I would recommend battery first... Having panels can save you a little on power but you will get a lot more by having a battery installed, having backup when power goes down is a little more important and a few inverters become painful if there isn't a battery installed. Personally, batteries first makes the most sense. Just know that your power usage will go up the smallest amount for charging, add panels as soon as you can.

If you’re into software development, one thing you could also think about when it comes to ESS is writing your own control loop. This is reasonably straightforward on Victron systems (see for eg this link) - in my setup I have a Cerbo GX running Venus OS Large, which gives me Node Red and I use that to control the ESS (Victron support for Node Red is excellent). I have two MPPTs (so no PV inverter), and I control when to direct PV power to the batteries and when to pull from the grid, using things like historical average loads, a solar PV forecast and data from EskomSePush to figure out how much energy I think I’ll need in the battery at different times of day. This helps to work around some issues that the standard ESS algorithms have, like pulling from the grid to charge a low SoC battery when it’s “obvious” that the solar PV for the day will take care of that later in the day.
As others have mentioned, using breakers/relays to control when you turn on power hungry appliances is also really helpful - I’ve been using the Shelly relays (in particular the Plus 1PM works well for me) to control my geysers & again you can integrate these into Node Red to do things like power on the geysers when you have excess solar PV.
I’m not familiar with support from other vendors like Sunsynk for Node Red, but you can install it on a Raspberry Pi so it’s not strictly locked into the Victron ecosystem. Worth a look if you have time & the interest in hand-tuning your system :)

The solution to that is to have a small portion of your panels on DC MPPTs, that will allow the system to restart again after the batteries were depleted.

I just realised one more factor that may become important when we hit stage 15...  AC coupled PV requires a grid to produce power.  If your AC coupled PV is on the output of your Victron, as mentioned above, no problem UNLESS your battery is completely depleted and your Victron inverter can't start...  Victron inverter off means no grid, means no AC coupled PV.  You need a generator or grid to get going again.
DC coupled PV is powered by the panels connected to it (I think).  So even with a dead battery, the MPPT should fire up and start charging it, allowing the inverter to start up afterwards.

I second the push for cc options. It's simply impossible to get your money back via an EFT if things go wrong. You don't have to go full merchant account with cc providers, but can even create online payment links via easy electronic payment means such as Yoco, Ikhokha, Snapscan, Zapper, etc. Payfast is great for enabling a number of payment options in one merchant account.
 
I run a business and constantly struggle with suppliers who are strictly EFT transfer. We prefer suppliers with cc options as a rule. What is forgotten is that there are "cash costs" even when you are not depositing physical cash. First there is the overhead (in the form of labour hours) for tracking and checking payments (for the purchaser this is an equivalent amount of labour on the payments side), matching to invoices, etc. Second is the vulnerability of PDF proofs of payment - a total wash, so you have to wait for money to hit the bank (part of the labour involved in point 1). There's a whole administrator whose job it is to track to this stuff. In many cases that salary is going to be higher than paying a 2.5% fee on all your purchases. If you're a serious business the fee comes down as you scale up (volume discounts). The inverse is true when you scale a manual system, you have to hire more administrators.  

Finally there is removing friction from customer conversion. Amazon famously added the 1-click purchase so customers didn't drop out at or before the cart. The more steps and friction involved in completing a purchase, the less likely you land that sale. 

Achmatk on Mybroadband feeds in and he is in Somerset West IIRC - if you are a member there perhaps ping him and get his first hand experiences

What size of arrays can you have? Surely CoCT you can but it depends on size if you can overcome the Admin fee and the bi-directional metering.

As P1k says, it's not completely off the battery.  What happens when the battery is full and the DC PV cut back and a load comes on is that the inverter starts to draw from the 48V DC bus to invert for the load and the MPPT ramps up its output to match.  This takes time, so some energy is effectively taken from the battery and then pushed back in a short while later.

Not completely, the MPPT is connected directly to the battery and inverter, but if you can keep the MPPT at a constant voltage when the batteries are full, you have effectively bypassed it. Although it does sometimes lead to problems with batteries that are sensitive to overvoltage, like Pylontech. Some batteries (like BSL) have the overvoltage threshold much higher than the charge peak voltage: 58V vs 54.5V respectively.
Inverters like Sunsynk and GoodWe can bypass the battery completely.

In terms of your question, "why add AC coupled PV, eg Fronius": 
I have both DC coupled (Victron MPPT) and AC coupled PV (Fronius) in my system.  There are some subtle differences between the two, for example if one is in ESS mode #1 (low state of charge), the PV power from the Fronius goes to loads first and only if there is excess is the battery charged.  The DC coupled PV goes to battery first and only assists loads once the state of charge is raised enough to clear ESS mode #1.  Which of these behaviours you want is likely a matter of personal choice.  I find having both quite advantageous.
Also consider:
* DC coupled MPPTs and the panels connected to them need to be close enough to the battery (and therefore the inverter) to keep the DC wiring short;
* AC coupled PV can be separated a long way from the battery.  If you have a biggish property or multiple buildings this may be a consideration.
* AC coupled PV on the output of the Victron *must* have a lower power rating than the Victron inverter itself.  You may not connect an 8kW Fronius on the output of a 5kW Victron for example.  In this configuration, the Fronius will continue to produce power if the grid is off.
* AC coupled PV on the grid side of the Victron has no Victron-enforced limits.  You may connect an 8kW Fronius on the grid side of a 3 or 5kW Victron, but then if the grid goes down your Fronius shuts off.
* DC coupled PV can be sized higher than your Victron inverter's limit, since it charges the battery directly, though obviously there are limits to how much power your batteries will accept too

I used a combination of the Efergy Engage Hub kit (purchased from Ellies) to measure total power consumption and a Sonoff POW2 switch to measure consumptions and peaks of varios appliances.

Good day all, 
I am looking at a 10kva Victron system with 14.3kw Solar MD battery and 16 x 540w panels in Durbanville - Cape Town. 
Any reason to rather go with the 10kva instead of 2 x 5kva Multiplus II? 
Apparently I don't need the Zeihl anti islanding relay with the 5kva units, but do need it with the 10kva MP II. 
Also only see the 3 and 5kva units on the City of Cape Towns approved inverter list and not the 10?
Would d be much appreciated if someone can give me advice and more info. 
Regards, 

Hi Bismuth, 
The Sunsynk & Victron Multiplus 2 inverters both have a backup port. The backup port in the Sunsynks case will power it's rated value. So 8kW Sunsynk will power up to 8kW backup load. The non essentials port will be able to make use of Grid power & or PV power depending if the grid is present or not above this 8kW value. It has pass through current value.  In the Victrons case it has something similar. 
Personally I prefer to decide what is essential & non essential by the use of Smart breakers & using the wide capacity Voltronics inverters. So something like an OG10.0 has 10kW of inverting power. That is plenty. If one wires everything onto the one load output this machine has & staggers the loads with smart breakers so these loads never come on at the same time, you then have a good chance of being in full control of the master plan of how & when you want to use your power. The good thing as well, you can blend all 3 sources of energy to these loads. You can send PV & or battery to the loads. 
It's just my preferred way to build a system & it's horses for courses out there, but one can see there is a lot of ways to best achieve your requirements & a variety of equipment on offer to get you there.

Hi All,

I'm new to the forum, but have done some reading and am readying myself to take the plunge on a system over the next few months, thanks to stage 4 loadshedding. 

My primary question is which system topology will be best to accomplish all three of:

a) Provide daily solar power to power and energy intensive devices such as geyser, pool pump, air conditioning, etc. on a schedule to match peak solar output (e.g. run my geyser from 11:00 to 14:00 on excess solar) - maximising on the "thermal batteries" concept
b) Provide sufficient power for other devices at other times (max anytime device would be an air fryer ~2kW) to provide cheaper energy than the grid
c) Provide a backup during load shedding (or continue to do a & b as though nothing has happened). 

My understanding is currently that a standard DC coupled hybrid topology e.g. with say a Victron Multiplus II (I'm also open to other suggestions on hardware) is the simplest full setup that meets the above criteria. 

Is my understanding correct that such a setup would be able to take the solar PV DC input and direct it straight to large appliances, i.e. if it's a 5kVA inverter and there is sufficient solar power on can run a geyser or aircon, etc? Is it not in such a case charging the battery with a built in MPPT (is it a built in MPPT?) and then discharging and converting it to AC? Or does it decide how much of the incoming DC to direct at either of those actions? 

If it does all of the above mentioned, what would be the reasons for adding a PV AC inverter (like a Fronius Primo)? Would it just have a higher combined power capacity (if say some heavy loads are being fed by the PV inverter and the Hybrid inverter is just "topping up")? Is my assumption correct that what makes such a system that much more expensive is not so much the addition of the PV inverter, but the need for (per the Victron website) "1.5 kWp installed AC PV power requires 4.8 kWh of battery storage"; which would make a 5kW system require >15kWh of batteries? Why does Victron show two separate grid tie inverters in the below topology under "ESS introduction"? I thought this just needed solar MPPT feed to ensure the "microgrid function" when the grid is down. 



A few other random questions:

- I'm assuming for a standard SA household one can safely ignore all 3-phase stuff online?
- Is there a good "plug and play" device one can use for a month or two before getting a system to log power consumption and do "right-sizing"?
- Does living in Cape Town with the new feed-in tariff change make any difference to system considerations?

Thanks in advance for your patience with the long post!