Are you prepared to try and reduce your energy consumption? Change to LED light bulbs for example. Or perhaps install a gas hob for cooking.
For this you will need to consider different times of the day and what your power requirements are at each of those times. This will yield the maximum amount of power that you will need at any particular time. It does not matter how long it is for. If there is a situation where you will need 50W for your Internet router, 200W for lighting, 3000W for the geyser, 2200W for a kettle and 1800W for your microwave oven all at the same time, then you have a peak power requirement of 7250W.
The maximum amount of power required is what you need to know to be able to choose the correct size inverter and the correct size storage (battery) system. If you need a peak power of 7250W, then best you get yourself an inverter capable of 8kW or more and you will need a storage (battery) system capable of producing a peak power output of 7250W.
If your maximum power requirement is 4800W for example, then a 5,5kW inverter will be sufficient and your storage will need to be able to deliver 4800W of peak power.
It is probably best to add on 10% or so as a safety margin.
For this you also need to consider how long you will use the power for. For example, you might want to consider what your needs might be from 01h00 to 05h00. That might be your Internet router (50W for 4 hours), your alarm system (50W for 4 hours) and your geyser might switch on during that time for 12 minutes (3000W for 10 Minutes). So you can calculate that in that particular 4 hour period you will need (50x4) + (50x4) + (3000x0.2) = 1000Wh over the 4 hours. If you switch the geyser off at night using a timer, then your 01h00 to 05h00 usage might be 400W.
During the period 17h00 to 18h00 you might be making supper and then your needs might be a lot greater if you will be using your stove, microwave, boiling a kettle. Just in that 1 hour you may need 8000Wh. A good way to check all these out is to take readings off your electricity meter. If your prepaid meter reading indicates that you have 236.7 units when you start cooking and 231.3 units an hour later, then you know that for that hour you require 5.4 units which equals 5.4kWh or 5400Wh of energy consumed.
You can also use your utility bill to calculate average daily energy requirement if you want a system that can supply energy for a full day. If you are paying for 600 units of electricity a month, that is around 20 units per day and therefore your daily consumption is about 20kWh or 20000Wh of energy.
The amount of energy required is what is needed to determine the capacity of your storage (battery) system.
Once you know how much power and how much energy is required, you can choose the correct battery for your storage. If, for example, you want to ensure you have battery capacity for 10 hours, your consumption is about 400 watts per hour and you need to cover a maximum power requirement of 2kW, then you will need a battery capacity of >4kWh (400W x 10h) that can deliver a maximum of 2kW peak. A 5kWh battery with 95% DoD and 0.5C rating will provide 4.75kWh of energy, will be able to supply 2.5kW of peak power and will be suitable for this application.
If, for example, you want to ensure you have battery capacity for 10 hours, your consumption is about 400 watts per hour and you need to cover a maximum power requirement of 4kW, then you will need a battery capacity of >4kWh (400W x 10h) that can deliver a maximum of 4kW peak. A 5kWh battery with 95% DoD and 1C rating will provide 4.75kWh of energy, will be able to supply 5kW of peak power and will be suitable for this application.
For most residential applications, a 0.5C or 1C battery is the best solution.
Building up as finances allowed was the route we chose. Initially we went for a system that mitigated against load shedding, then went for a system that would save grid costs. This is where we made our first mistake by not immediately getting the best inverter for both of these scenarios. Do not make this mistake - you want a blended Parity Hybrid inverter that meets your maximum power needs as the heart of your system right from the start.
Step 1 - Install a basic system to cover your essential loads like your alarm system, your Internet router and to be able to boil a kettle during load shedding outages.
1.1) Install an inverter. Either a 5.5kW or 8.8kW Parity Hybrid inverter depending on power requirements [Recommended Sunsynk 8.8kW Parity Hybrid]. Connect your essential devices to the "UPS" output and keep other devices on the same "Grid" connection as the inverter.
1.2) Install a suitable size battery to cover essential services during load shedding. The main choice here will depend on the outage duration that you wish to cover, your total consumption during that outage and the maximum power required. [Recommendation 1 for small system with only low power critical devices being covered: 1x Pylontech US3000C battery. This will give you about 1.8kW of power and 3.3kWh of usable energy]. [Recommendation 2 for medium system with most of the house load being covered and requiring high power loads to be supplied for short duration: 1x Sunsynk 5.12kWh battery. This will give you about 5kW of power and 5kWh of usable energy]
Step 2 - Install some solar panels so that you are recharging the batteries using solar energy and not grid energy
Step 3 - add more solar and storage and connect your entire house to the "UPS" output.
Step 4 and more - keeping adding batteries and solar panels.