Key takeaways
- System size (kW) ≈ yearly kWh ÷ 1,400. Panels ≈ kW ÷ 0.44.
- Output per kW varies: about 1,550 to 1,650 kWh in Nelson/Marlborough, 1,100 to 1,250 in Southland.
- Allow about 2 m² of roof per panel. A 6.6kW system needs about 30 m².
- Match size to what you'll use in daylight, not your whole bill.
The sizing formula
System size in kW is your yearly kWh divided by how many kWh each kW generates in your region. Using the NZ average of 1,400: a home using 8,400 kWh a year needs about 6kW, which rounds to the standard 6.6kW (15 panels).
| Household | Yearly use | System size | Panels (440W) |
|---|---|---|---|
| 1–2 people, efficient | 4,000 – 6,000 kWh | 3 – 4kW | 7 – 9 |
| Average 3-bedroom | 7,000 – 9,000 kWh | 5 – 6.6kW | 12 – 15 |
| Large family (4–5 people) | 10,000 – 14,000 kWh | 8 – 10kW | 18 – 23 |
Output per kW by region
Sunnier regions generate more from the same system. Solar Scout's figures run from 1,550 to 1,650 kWh per kW a year in Nelson and Marlborough down to 1,100 to 1,250 in Southland.
| Region | kWh per kW per year |
|---|---|
| Nelson / Marlborough | 1,550 – 1,650 |
| Bay of Plenty | 1,450 – 1,550 |
| Auckland | 1,350 – 1,450 |
| Canterbury | 1,300 – 1,450 |
| Wellington | 1,250 – 1,400 |
| Southland | 1,100 – 1,250 |
How much roof space do I need?
A modern 440W panel is about 1.7 m by 1.1 m, so allow about 2 m² of usable roof per panel including gaps. A 6.6kW system of 15 panels needs about 30 m², and 10kW about 46 m².
Arrays over 40 m² can still skip a building consent, but only with a design carried out or reviewed by a Chartered Professional Engineer. See the consent guide.
Should I size for my whole bill?
Not necessarily. Solar you use at home saves about 40.6c a kWh; solar you export earns 8c to 24c. Sizing well beyond your daytime use adds panels that mostly export at the lower rate. If you plan an EV or heat pump, size for that future use.
Finding your yearly kWh
Your retailer's app or online account shows your usage for the last 12 months. That's more accurate than working back from the bill, because bills include daily fixed charges.
Frequently asked questions
How many solar panels does a 3-bedroom house need in NZ?
Typically 12 to 15 panels (5 to 6.6kW) for a home using 7,000 to 9,000 kWh a year (Solar Scout).
How many panels is 6.6kW?
15 panels at 440W each, about 30 m² of roof. See the 6.6kW package.
How much power does one solar panel make in NZ?
A 440W panel at the NZ average of 1,400 kWh per kW makes roughly 600 kWh a year.
Can I put panels on east and west roofs?
Yes. Splitting panels east and west spreads generation across the morning and afternoon, which can suit daytime use. The survey checks output for your roof.
Sources
- Solar Scout, How many solar panels do I need (updated 1 Apr 2026) (checked 1 Apr 2026)
- Canstar NZ citing MBIE Quarterly Survey of Domestic Electricity Prices to 15 Feb 2026 (checked Feb 2026)
- Solar Scout, Buy-back rates NZ (updated 31 Aug 2026) (checked 31 Aug 2026)
- EWRB, Solar panel consent exemption changes (checked Sept 2026)
General information, not financial advice. Prices and rates change; each figure shows where it came from and when it was checked.