Why system size matters
Oversizing wastes capital. Undersizing leaves money on the table. The right system size is the one that offsets the most electricity you can afford to offset, at the best possible payback.
The simple rule: your bill tells you the size
| Monthly bill | Recommended system | Panels (460Wp) | Capex estimate |
|---|---|---|---|
| R500 – R800 | 2 kW | 5 panels | R35,000 – R45,000 |
| R800 – R1,500 | 3 kW | 7 panels | R50,000 – R65,000 |
| R1,500 – R2,500 | 5 kW | 11 panels | R75,000 – R95,000 |
| R2,500 – R4,000 | 8 kW | 18 panels | R110,000 – R140,000 |
| R4,000+ | 10–15 kW | 22–33 panels | R145,000 – R200,000 |
Prices include VAT, installation, CoC and basic string inverter. Battery excluded. Based on 2026 market rates.
The calculation behind the table
The sizing formula targets 80% offset of your annual kWh consumption:
kWh consumed per month = Bill ÷ Tariff Annual kWh = Monthly kWh × 12 System kWp = (Annual kWh × 0.80) ÷ (PVGIS yield × 0.80 loss factor)
Where PVGIS yield is city-specific (e.g. Johannesburg: 1,820 kWh/kWp; Cape Town: 1,780 kWh/kWp).
Should I add a battery?
A battery answers one question: do you want power during load-shedding?
- Without battery: system shuts down when Eskom cuts power (safety requirement for grid-tied systems). You save during daylight hours only.
- With battery: you continue using solar-stored power during load-shedding and at night. Self-consumption rises from ~60% to ~85%.
A 5.12 kWh LiFePO4 battery (the most popular size) costs R25,000–R40,000 installed. It's worth it if you have Stage 4+ load-shedding regularly.
Roof space check
A standard 460Wp panel is roughly 2.1 m × 1.1 m (about 2.3 m²). For a 5 kW system (11 panels) you need approximately 26 m² of usable roof space, ideally north-facing with no shading between 9am and 3pm.
Get your exact system size
Use our AI-powered solar calculator — enter your bill and city, and we'll compute your exact system size, panel count, payback period and 25-year saving using PVGIS irradiance data for your specific location.