That all depends on what you want to run on the system and at what times of the day, and for how long you run each device.
Running a Fridge, TV and WiFi only requires a small solar inverter and a few solar panels to run during the day when the sun is shining, however at night the fridge will drain the battery at a steady rate, therefore the battery needs to have enough capacity to last the night.
That been said, most new Hybrid inverters do not require large batteries or batteries at all if that is your choice. A hybrid system can use the solar power while the Sun is shining and if you don’t have batteries, it will automatically switch to utility power to keep the devices running at night. This way you can run your heavy loads during the day and import a small amount of power from the grid for night time. If you want to go Off-Grid as much as possible, then you will require a battery bank for the evenings.
How much battery storage do I need for night time?
Lets say a fridge is 150W. This means it will use 150 watts per hour of electricity. If you have a 200w solar panel you can run the fridge for free during the day. However at night time (+-16 Hours depending on location, shadows etc) you will need 150w/Hr x 16Hrs night time = 2400w. That is a fair size battery just to run a fridge.
Other smaller devices use a lot less power and run for shorter times. A TV is +- 100w but you only use it for 8 Hrs at night. = 800w. A kettle is normally 2000w but you only use it for 5 minutes = 166w Each time you boil it. Twice a night – 333w. The same goes for an Iron 2000w but you might use it for 1 hr = 2000w
Now you add the total watts together to get a rough estimate of your battery requirements. In our example our total is 5533 Watts of power we require. This means we need 2 x 5kwh batteries or a 1 x 10kwh or bigger battery. Just to run those few devices.
Another factor to consider is how much load you will put on the Battery. If you have a 25v 2.5kw 100ah = 2500 watt lithium battery , it means you can max draw up to 100 amps x 25v = 2500 watts. So if you have a kettle and microwave etc running it will trip the battery and not the inverter. Therefore it is wise to work out you max load and work from there. To run a geyser of 4000 watts and microwave will trip a 5kw battery. To increase the max amp draw you need to add another battery in parallel which doubles the amp draw, or buy a 10kw battery which has a 200amp draw.
How about my geyser?
A 200L geyser typically uses 3000w of power / Hour. That equates to 9000w you require to heat the geyser for 3 hours. Its just not feasible to run your geyser at night. The solution is to put a timer on the geyser and only turn it on when the sun is shining or the inverter loads are low, Another solution is to install a solar geyser so that it runs independently of the inverter system and requires no power it self.
Can I use my stove?
If your inverter is big enough then YES, however it will drain your battery very fast at night, therefore rather use it during the day or purchase a Gas stove . You will also need quite a few solar panels to run it. A plate is normally 1500w and the oven 4000-7000w depending on the size.
How many solar panels do I need? What Size Solar System?
If you only want to charge your battery for night time then – battery capacity divided by the number of sun hours. eg : A 2700 watt lithium battery / 8 hrs (Sunshine) = 337.5 watts per hour we need. That means you need at least a 350 solar panel to charge the battery to full on a clear sunny day. If the weather is overcast or slightly cloudy the performance of the panels goes down dramatically, which means you will need more panels just in case. However you also need to consider self consumption so it is always bettery to have more panels.
How much power do my appliances consume. These figures are based on my own investigation based on consumption per hour
Geyser 3000-4000 Watt
Stove top 1500 watt per plate
Oven 3500-5000 Watt
Deepfreezer 100 watt
Fridge 100-150 watt
Shop fridge 700 watt
Iron 1200-2200 watt
Kettle 1500 watt
Washing machine 1500 watt
Tumble dryer 1500-2200 watt
Each LED light 8-20 watt
Each normal light bulb 50-100 watt
Laptop 80 watt
Computer 250-350 watt
Gaming computer 450-600 watt
Each TV 100 watt
WiFi / Fibre router 9 watt