The inverter is the heart of the system and possibly the most important component to get right. There are different types of inverters available, but they mostly into two categories - inverters that switch between the ac and DC inputs to power the output and inverters that are able to combine both ac and DC inputs.
This type of inverter can do it all and as the best option when you are putting in a system that may change incrementally from being purely for load shedding, to reducing grid costs to finally going fully off grid. The key attributes are that they can:
feed back to the grid if that is allowed (if FIT - feed in tariffs - are available in your area you can offset some of the system cost by exporting excess capacity)
they can accept solar panel (PV) power
they can accept wind turbine power
they can be connected to most generators
they do not switch between DC and ac -instead any shortfall from DC is supplemented by only the shortfall from the grid connection or generator input
they have more programming features to customise setup for specific needs
A huge positive that most (beware not all) have a UPS quality load output that is able to switch fast enough to allow the connection of electronic devices like routers and PCs without the power being interrupted to them during switchover between DC and ac inputs - due to the blended nature of the inputs.
You need to know the maximum power that you will ever need to draw from the inverter. And then it makes sense to go a little higher. There are 2 main reasons for this.
The first is that there may be some eventualities that you have not thought of and having the extra power headroom could end up being invaluable.
The second is that you do not want to run the inverter at the limit of its capabilities for extended periods or too often. They are complex systems that you want to protect from overloading or resetting as much as possible. An effective way of doing this is to allow them to operate in their comfort zone.
A concern for going for a larger specification inverter is the extra cost. Let us take the difference between a Sunsynk 5kW and Sunsynk 8kW inverter. As at 15/02/2023, the 5kW costs ~R26000 and the 8kW costs ~R42000. The 8kW is therefore ~R16000 or 61% more expensive than the 5kW. If your calculations had indicated that your maximum power draw would be 5kW, you would be tempted to say that the extra ~R16000 or 61% is not worth it. However, now you start adding in the rest of the system - say ~R70000 for 10kWh of storage, ~R52000 for 6kWp of solar panels and ~R10000 for installation. Now the 5kW system as a whole is ~R 158000 and the 8kW system is ~R174000. The difference is still R16000, but the percentage difference in cost is now 10% with 60% more power available from the inverter.