How Many Solar Panels Do You Need? Roof Space and kWp Explained (2026)
Panel count is the wrong question. Roofs are sized in kilowatt-peak and in square metres, and the number of panels falls out of that. Here is how to work out what your roof can actually carry and what it needs to.
Work in kWp, not in panels
A “14 panel system” means nothing until you know the panel. Fourteen 600W modules is 8.4kWp. Fourteen 450W modules is 6.3kWp. That is a third less generation from the same panel count and roughly the same roof area.
So start with the array size you need in kWp, then divide by the module wattage to get the count.
How much array do you need?
The array has two jobs: carry the daytime load and refill the battery before sunset. Size it on a poor winter day, not an annual average.
- Daily consumption. Monthly kWh from your bill, divided by 30.
- Winter yield per kWp. In most of South Africa a well-oriented array delivers meaningfully less in June than in December. Design against the winter figure so the system does not disappoint for half the year.
- Divide. Daily consumption divided by winter yield per kWp gives the kWp you need.
As a sanity check, most family homes end up between 3kWp and 10kWp, which is 5 to 17 modules at 600W.
How much roof does that take?
A modern 600W to 635W module occupies roughly 2.6 square metres. Add spacing, walkways and edge setbacks and it is sensible to plan on about 3 square metres of roof per module in practice.
| Array size | 600W modules | Rough roof area needed |
|---|---|---|
| 3kWp | 5 | about 15 m² |
| 3.6kWp | 6 | about 18 m² |
| 6kWp | 10 | about 30 m² |
| 8.4kWp | 14 | about 42 m² |
| 10.8kWp | 18 | about 54 m² |
| 14.4kWp | 24 | about 72 m² |
Those are usable, unshaded, correctly-oriented square metres. Total roof area is always larger than usable roof area.
What actually limits your roof
- Orientation. North is best in South Africa. East and west both work with a yield penalty. South-facing is usually a last resort.
- Shading. A chimney, a tree or a neighbouring wall can pull down a whole string, not just the shaded module. This is what MPPT layout and, where needed, optimisers are for.
- Structure. The roof has to carry the array and the wind load on it. Older timber and some sheeting need checking before anything is fixed to them.
- Roof type. Tile, IBR and cliplock each take different mounting hardware. Cliplock is generally the easiest, tile the most labour.
- Plane count. An array split across two or three orientations needs an inverter with enough MPPTs to track each independently.
Panel choice: does wattage or technology matter more?
Both, in that order, but for different reasons. Higher wattage per module means fewer modules, fewer mounting points and less labour for the same kWp, which is what you want on a small roof. Cell technology affects how the panel behaves over its life: N-Type modules generally hold output better at high temperature and degrade more slowly than PERC, which is worth paying for on a hot roof you intend to keep for twenty years.
| Panel | Output | Technology | Price incl. VAT |
|---|---|---|---|
| JA Solar JAM72S30-600/MR | 600W | Bi-facial PERC | R2 110 |
| Canadian Solar CS6W-635T | 635W | Bi-facial N-Type TOPCon | R2 230 |
Bi-facial modules earn their premium only where light can reach the rear face: ground mounts, open-back carports, light flat roofs. Flush-mounted on tile, treat the rating as the front-face figure.
Frequently asked questions
How many solar panels do I need for a 5kW system?
A 5kW inverter is usually paired with 3kWp to 6kWp of array, which is 5 to 10 modules at 600W. The inverter rating sets the ceiling on instantaneous output; the array sets how much energy you harvest.
Can I have more panels than my inverter rating?
Yes, within the inverter’s stated maximum PV input. Modest oversizing is normal practice and improves winter and cloudy-day output, at the cost of some clipping on the brightest summer days. Check the specific inverter’s limit.
Do panels work on a south-facing roof?
They generate, but with a meaningful yield penalty. If the north-facing area is limited, splitting an array east and west usually beats going south.
What if my roof is too small?
Use higher-output modules to get more kWp into the same area, and size the battery to shift what you do generate into the evening peak, which is where the expensive units are.
Next step
Read the full sizing guide, use the system designer, or browse panels and complete packages.
