Most people start with the wrong question. "How many panels do I need?" depends on two other answers first: how much power you use, and what you want the system to do for you. Here is the order we work through it on a site visit.
1. Work out what you use
Your municipal bill or prepaid history shows units used, in kilowatt-hours (kWh). Divide the monthly figure by 30 to get a daily number. A typical Pretoria family home uses somewhere between 15 and 35 kWh a day, but the range is wide.
If you only know what you spend, divide the rand amount by your rate per unit. Municipal rates in Gauteng sit roughly between R3 and R4 per kWh including VAT, and they change every July, so check yours.
2. Decide what the system is for
- Backup only: keep essentials on during outages. Battery and inverter matter most, panels are optional.
- Save and back up: use solar in the day, store some for the evening, and keep essentials on. This is what most homes choose.
- Use as little grid power as possible: more panels and a bigger battery, with the grid as a top-up.
3. Size the inverter from your peak load
The inverter has to handle everything that can be on at the same time. Add up what will run on it: a fridge, lights, Wi-Fi and a TV come to well under 1 kW, but a kettle alone draws about 2 kW and a borehole pump can spike far higher when it starts.
That is why geysers, ovens and stoves usually stay on the grid side of the board. A 5 kW inverter covers most homes, 8 kW suits larger households or homes with pumps.
4. Size the battery from the hours you want
Battery size is a simple sum: the power of your essentials multiplied by the hours you want them on. Lights, Wi-Fi, a fridge, a TV and the gate draw about 500 W on average, so four hours needs about 2 kWh, and a full night needs closer to 5 kWh.
Lithium iron phosphate (LFP) batteries are sold in modules, commonly around 5 kWh each, and can be used to most of their capacity day after day.
5. Size the panels from your daytime use
Gauteng gets roughly five to five and a half hours of full-strength sun a day averaged over the year. After real-world losses, each kilowatt of panels (kWp) produces about 4 kWh a day. A home that wants to cover 12 kWh of daytime use needs about 3 kWp, which is six panels of 565 W.
The roof sets the upper limit. North-facing is best, but east and west roofs work well too, with a little less output.
Try it with your numbers
Our system sizer runs these sums for you and shows a rough price range. Treat it as a starting point: a site visit is what turns it into a design you can rely on.
Want numbers for your own home?
The system sizer gives you a first estimate in two minutes. A site visit turns it into a fixed quote.
