Size.Solar
Solar yield in Johannesburg
Estimated annual solar yield is 1704 kWh per kWp per year. A 400W panel is estimated to produce 682 kWh/year, or 1.87 kWh/day, after modelled system conversion losses.
Provider-backed estimate
NLR PVWatts 8.5.0, using TMY dataset (2022 release) weather data. The model assumes north-facing panels at 26° tilt, 0° azimuth, and 14% system losses.
Retrieved . Compare tilt and direction.
The estimate is before site-specific roof angle, shade, weather, and equipment factors.
Current estimate
Annual savings
R37,472
Use covered
98%
Draw panel areas next. No sign-in needed.
Your system settings
Annual bill savings
R37,472
Average monthly bill value of R3,123, based on monthly production and capped to the 600 kWh/month use you entered.
Electricity use covered
98%
Surplus in higher-production months: 474 kWh/year. Export credits or batteries may add value.
Annual output
7,500 kWh
Daily output
~21 kWh
System size
4.4 kW
Panels needed
11 panels*
Will this system fit your roof?
Keep these inputs while you outline usable roof space and refine the estimate. Compare installers when the roof plan is ready.
Monthly production breakdown (kWh)
Next accuracy check
Check this estimate against your roof
The figures below are an example starting point for Johannesburg: 11 panels at 400W, about 4.4 kW, and a 600 kWh/month electricity-use target. Review your current panel wattage, panel count, and electricity use in the calculator above before opening the roof planner or comparing installers.
- Example system
- ~4.4 kW
11 panels for a 600 kWh/month home before roof, inverter, and battery constraints.
- Output per panel
- 682 kWh
Estimated annual AC electricity from one 400W panel after modelled system losses.
- Bill value/year
- R37,472
Annual value at about ZAR 5.33/kWh, capped to the electricity use you can actually offset.
- Weakest month
- Feb
50 kWh from one 400W panel; check this month before sizing essential loads.
Roof fit
Confirm usable roof planes, shading, inverter limits, and battery needs before accepting a final layout.
Bill fit
Adjust panel count and monthly use above so savings are capped to electricity you can offset.
Quote check
Ask suppliers to show winter output, assumed losses, and any export-credit value separately.
Production evidenceShow monthly output and model assumptionsOpen this when checking winter production, irradiance, losses, or the source assumptions behind the quote handoff.
Monthly model
Monthly output and winter risk
The calculator is useful when it shows the weak months, not just a flattering annual number. Use the table to check whether winter output still supports the loads you care about.
- Best month
- Sep
66 kWh from one 400W panel
- Lowest month
- Feb
50 kWh from one 400W panel
- Solar resource
- 6.2 kWh/m²/day
2269 kWh/m² annual irradiance
- Model checks
- 19.5%
Capacity factor, 75.1% performance ratio, 714 kWh DC before conversion
| Jul | Aug | Sep | Oct | Nov | Dec | Jan | Feb | Mar | Apr | May | Jun |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 61 kWh | 63 kWh | 66 kWh | 63 kWh | 58 kWh | 52 kWh | 52 kWh | 50 kWh | 52 kWh | 50 kWh | 59 kWh | 56 kWh |
Model basis
The model uses north-facing panels at 26° tilt, true north orientation, and 14% system loss. Typical 600 kWh/month electricity costs are R2,190 - R4,600 (typically R3,200) using 2024-2025 cost data.
Solar production data provided by NLR PVWatts 8.5.0. Weather source: NSRDB PSM V4 Meteosat Prime Meridian tmy-2022 1.0.0; nearest source point 0.3 km from the city coordinates.