What Size Solar System Do I Need?
What Size Solar System Do I Need? The most often asked question. 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. 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.
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 : 2700 watt / 8 hrs = 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.
Now lets add a 150w fridge. We need 337.5 watt for charging the battery and another 150 watt to run the fridge = 487.5 watt (We will need at least a 550w panel just to be safe)
Now lets add a washing machine, typically 1000 watt to 2000 watt. That means you will need 487.5 watt + 1500 w = 1987.5 Watt we need. That would be 4 big 550w panels.
The big question, my geyser. Typically 3000 watt . However it doesn’t mean you now need 1987.5 watt + 3000 watt, unless you want to run everything simultaneously. You would only need 487.5 watt + 3000w and just turn the geyser off when you want to run heavy appliance (You can set the geyser on a timer to only run for 3 hours in the afternoon, after all the washing etc is done)
So the bottom line is you need enough panels to charge the batteries, run the essential, and be able to run the heaviest appliances individually.
Always remember on an overcast day performance goes down so always add extra panels unless you plan on staying grid tied or you have big battery banks.
How much power do my appliances consume
These figures are based on my own investigation based on consumption per hour
- Geyser 3000 Watt
- Stove top 1500 watt per plate
- Oven 3500-7000 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 1500-2000 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
Example
Still to come
Distribution Board DB Wiring

Advise – What Size Solar System?
That all depends if you want to reduce your electricity bill or go totally off-grid. Reducing your account could just require a small solar package to run your essentials, however going off grid will require a lot of investment capital.
Do not cancel your utility account until you are confident about your solar system. There could be many rainy days which means you will need a very large battery bank or pull power from the utility.
Always have a Generator as backup