How many solar panels does a NZ house need?

It depends on your power use and target offset. A typical home using 8,000 kilowatt-hours a year and covering most of it needs roughly a 6 kilowatt system, about 14 to 16 modern panels. This calculator sizes it from your own usage and panel wattage.

How much roof do I need for solar?

Allow roughly 2 square metres per panel, so a 15 panel system needs around 29 square metres of unshaded, ideally north-facing roof. Orientation and shading matter a lot, so a site assessment from an installer will confirm what your roof can fit.

Should I size solar to cover all my power?

Not usually. Covering 100 percent means exporting a lot of cheap midday power and paying retail in the evenings. Many households size for 70 to 90 percent of use, and add a battery or shift appliance use to midday to lift how much of their own solar they consume.

Solar Panel Count Calculator

This calculator works out how many solar panels you need for your home in New Zealand, along with the system size in kilowatts, the roof area required, and the power the system should generate in a year. Solar is increasingly popular here as power prices climb, but sizing a system is confusing because it depends on how much electricity you use, how much of it you want to cover with solar, the wattage of the panels, and how much sun your region gets. Oversize the system and you spend more than you need and export cheap power to the grid; undersize it and you keep buying expensive power from the retailer. This tool gets you to a sensible size quickly. You enter your annual power use in kilowatt-hours, which you can read off your bills, the share of that use you want solar to cover, the wattage of the panels you are considering, and the annual generation per kilowatt of system for your area, which in much of New Zealand is around 1,200 to 1,400 kilowatt-hours per kilowatt installed. The calculator returns the number of panels, the system size in kilowatts, the approximate north-facing roof area needed, and the estimated annual generation. Use it to brief installers, compare quotes on a like-for-like basis, and decide whether to add a battery. Bear in mind that solar generation is highest in summer and midday, while much home use is mornings and evenings, so a battery or smart use of appliances improves how much of your own power you actually use. This is a planning estimate; a reputable installer will assess your roof, shading and orientation precisely.

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Annual power use (kWh)

Share to cover with solar

Panel wattage (W)

Generation per kW (kWh/yr)

12 panels

solar panels needed

System size4.9 kW

Roof area~24 m²

Annual generation~6,400 kWh

Generation per kW is region-dependent (~1,200-1,400 kWh in much of NZ). Solar peaks midday; a battery improves self-use. A planning estimate.

How it works

The system size in kilowatts is your annual use times the share you want to cover, divided by the annual generation per kilowatt for your area. The number of panels is that system size in watts divided by the panel wattage, rounded up. Roof area assumes about 2 square metres per panel, and annual generation is the system size times the generation per kilowatt.

Worked example

To cover 80 percent of 8,000 kilowatt-hours a year, at 1,300 kilowatt-hours per kilowatt, you need about a 4.9 kilowatt system. With 440 watt panels that is about 12 panels, needing roughly 24 square metres of north-facing roof, generating around 6,400 kilowatt-hours a year, which matches the 80 percent target. A larger offset or weaker sun would need more panels.

Related calculators

Solar Panel Payback: when solar pays off.
Solar Battery Payback: adding a battery.
Electricity Cost: appliance running costs.
EV Charger Payback: charging at home.

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