Solar system size calculator
Tick what must keep running, choose the hours of backup and enter your monthly units. You get a rough inverter, battery and panel size, and can send it straight to installers for quotes.
Solar calculator and quote request
Tell us what you need and where. An installer or supplier who works in your area quotes you directly. Free, no obligation.
Size it roughly (optional)
Tick what must keep running when the power is off. The estimate goes into your request so installers can quote closer to what you need.
5.0 kWh per kWp a day
Tick a few loads or enter your monthly units to see a size.
A rough guide only. An installer confirms the size after looking at your bill, roof and distribution board.
Most people want solar for one of three things: to keep the lights on during power cuts, to cut the electricity bill, or both. The size that does the job depends on what you run, for how long, and how much sun your roof gets.
How the calculator works
Tick the loads you want to keep running during a power cut and choose the hours of backup. The calculator adds up the typical peak draw of those loads to suggest an inverter size in kVA, and their average draw over the hours you chose to suggest a battery size in kWh. Enter the units you use a month and it divides them by the sun in your province to suggest how many kWp of solar panels would cover them.
- Inverter (kVA): peak draw of the ticked loads plus 25% headroom, rounded up to a common size.
- Battery (kWh): average draw × hours, divided by 0.9 for usable capacity, rounded up to a common size.
- Panels (kWp): monthly kWh ÷ 30 ÷ (local yield × 0.8 for heat, dust and losses).
Typical sizes for South African homes
| What runs | Inverter | Battery | 550 W panels |
|---|---|---|---|
| Lights, Wi-Fi, TV, fridge and gate | 3–5 kVA | 5 kWh | 2–4 panels |
| Above, plus kettle, microwave and home office | 5 kVA | 5–10 kWh | 6–10 panels |
| Most of a family home, geyser on a timer | 8 kVA | 10–15 kWh | 10–16 panels |
| Large home with pool pump and borehole | 10–12 kVA | 15–20 kWh | 16–24 panels |
| Small business or farmhouse with workshop | 12–16 kVA, often three-phase | 20–30 kWh | 20–36 panels |
Geysers, stoves, pool pumps and air conditioners draw a lot of power. Many households keep the geyser on the grid or move it to a solar geyser, which shrinks the inverter and battery needed.
Sun across South Africa
The Northern Cape and North West get the most sun, Gauteng and the Free State are close behind, and the KwaZulu-Natal and southern Cape coasts get the least. A kilowatt-peak of panels makes roughly:
- Gauteng: about 5.2 kWh a day
- Mpumalanga: about 5.0 kWh a day
- North West: about 5.5 kWh a day
- Limpopo: about 5.4 kWh a day
- Northern Cape: about 5.9 kWh a day
- Free State: about 5.5 kWh a day
- KwaZulu-Natal: about 4.6 kWh a day
- Eastern Cape: about 4.8 kWh a day
- Western Cape: about 5.0 kWh a day