What size solar system do I need?
Most South African homes need between 3 kW and 10 kW of solar panels. To size a system, divide your daytime electricity use by your province's peak sun hours and then by 0.8 to allow for real-world losses. A Gauteng home with a R3 500 monthly bill using about 40% of its electricity during daylight needs roughly 2.2 kW of panels, a 3 kW inverter and about 25 kWh of usable storage for the evening. That array produces around 5 495 kWh a year at Gauteng's 8.5 peak sun hours per day, worth roughly R17 033 at current tariffs, and costs R33 207 to R39 848 installed. Roof area is often the real constraint: usable north-facing roof fits about 0.21 kW per square metre.
Your estimate
Worked example
A Gauteng home, R3 500 a month, 45 m² of usable north-facing roof, roughly 40% of consumption during daylight.
| Monthly consumption | 1129 kWh |
| Used during daylight | 452 kWh |
| Peak sun hours (Gauteng) | 8.5 per day |
| Array needed | 2.2 kW |
| Roof can hold | 9.5 kW |
| Recommended array | 2.2 kW |
| Inverter | 3 kW |
| Usable battery | 25 kWh |
| Annual production | 5 495 kWh |
| Annual saving | R17 033 |
| Installed cost | R33 207 – R39 848 |
How this is calculated
Bill to kWh: monthly spend ÷ R3.10 per kWh. Municipal tariffs are usually blocked, so this is a mid-block figure for a typical urban domestic customer rather than your exact rate.
Array size: daily daytime kWh ÷ (peak sun hours × 0.8). The 0.8 is the standard performance ratio covering heat, soiling, wiring losses and inverter conversion.
Roof limit: 210 W per usable m², which reflects current mono-PERC module efficiency.
Battery: evening consumption ÷ 0.9, since usable lithium capacity is about 90% of nameplate.
Cost: R15 000 to R18 000 per kW installed, the same range published on our solar cost page.
This is an estimate for comparing quotes, not a system design. Shading, roof pitch and orientation, your actual tariff and the state of your distribution board all matter and none of them are inputs here. A certified installer will survey the property before finalising anything.
Sizing: common questions
What size solar system do I need for my house?
It depends on your daytime consumption, not your total bill. Divide monthly kWh by 30, multiply by the share you use in daylight, then divide by your province's peak sun hours and by 0.8 for losses. A R3 500 monthly bill in Gauteng typically works out to a 2.2 kW array with a 3 kW inverter.
How many solar panels fit on my roof?
Roughly 210 watts per usable square metre of north-facing roof with current panels, so 40 m² holds about 8.4 kW. Only unshaded, north-facing area counts. East and west-facing roof still works but produces meaningfully less across the day.
What are peak sun hours and why do they matter?
Peak sun hours are the number of hours per day equivalent to full-strength sunlight. They range from 7.4 in KwaZulu-Natal to 9.6 in the Northern Cape. Each 1 kW of panels produces about that many kWh per day before losses, which is why the same system produces different amounts in different provinces.
Should I size the system to cover my whole bill?
Usually not. Solar only displaces electricity you use while the sun is up, so oversizing the array to cover night-time consumption means exporting or wasting the surplus. Size the panels to your daytime use, then use the battery to shift some of that into the evening.
Is this calculator accurate enough to buy from?
It is a sizing estimate, not a design. It does not account for shading, roof pitch and orientation, your specific tariff structure, or the state of your distribution board. Use it to sanity-check the quotes you receive, and expect a certified installer to survey the property before finalising a design.