How Much Solar Power Will I Generate in NZ? (By Region)

Auckland (6.6kW)

Christchurch (6.6kW)

Dunedin (6.6kW)

[1] 1. Wellington ranks #2 in the country

Wellington has a reputation for wind and rain. So how does it produce 1,431 kWh/kWp, second only to New Plymouth?

Two reasons. First, wind cools the panels. Solar panels lose 0.3-0.5% efficiency for every degree above 25°C. On a still summer day in Hawke's Bay, panels can hit 65°C and lose 12-20% of their rated output. Wellington's constant breeze keeps panels at 40-50°C, reducing losses to 5-13%.

Second, Wellington benefits from clear east-coast weather patterns. Despite fewer sunshine hours than Blenheim or Nelson, when the sun is out in Wellington, the air is clean and the irradiance is strong.

[2] 2. Blenheim has the most sun but not the most output

Blenheim logs 2,521 sunshine hours per year, more than any other NZ city. Nelson follows with 2,497. Yet Blenheim ranks third for specific yield (1,407 kWh/kWp) and Nelson ranks eighth (1,361).

The explanation is latitude. At -41.5°, the sun sits lower in the sky than in Auckland (-36.8°). Each sunshine hour in Blenheim delivers less irradiance than one in Auckland, because the light passes through more atmosphere at a lower angle. Sunshine hours alone do not tell the full story.

[3] 3. Even Invercargill beats London

Invercargill is NZ's lowest-ranked city at 1,137 kWh/kWp. London produces 1,154 kWh/kWp. That is close, but the point stands: every NZ city from Whangarei to Queenstown comfortably outperforms the UK, which has over a million solar installations.

If solar works in London, it works in every NZ city. Full stop.

Roof direction and pitch

A north-facing roof at 30° tilt is ideal. East or west-facing roofs lose about 10-15%. South-facing roofs lose 25-30% and are generally not recommended.

Shading

Even partial shading from trees, chimneys, or neighbouring buildings can cut output by 10-25%. Modern microinverters and optimisers reduce this impact, but they do not eliminate it entirely. A pre-install shade analysis is essential.

Panel temperature

Panels lose 0.3-0.5% efficiency per degree above 25°C. On a hot still day, panel surface temperatures can reach 60-70°C, reducing output by 12-22%. Wind, elevated mounting, and lighter-coloured roofing all help keep temperatures down.

System age and degradation

Solar panels degrade at roughly 0.3-0.5% per year. After 25 years, expect about 87-92% of original output. This is already factored into manufacturer warranties (most guarantee 80-85% at 25 years).

Inverter efficiency

Your inverter converts DC from the panels to AC for your home. Modern inverters run at 96-98% efficiency. The remaining 2-4% is lost as heat. String inverters, microinverters, and optimisers each handle partial shading differently.

How much solar power will a 6.6kW system generate in Auckland?

About 9,180 kWh per year, or 25.1 kWh per day on average. In summer, expect around 35-39 kWh per day. In winter (June), output drops to about 11 kWh per day.

Is the South Island good for solar?

Yes. Christchurch produces 1,340 kWh/kWp, which is only 4% less than Auckland. Nelson and Blenheim are among the sunniest cities in NZ. Even Dunedin and Queenstown produce more solar power per kW than London.

Why does Wellington rank so high for solar output?

Wind cooling. Solar panels become less efficient as they heat up. Wellington's constant breeze keeps panel temperatures 10-20°C cooler than in sheltered North Island cities, which offsets the slightly lower sunshine hours.

How much does solar output drop in winter?

It depends on your location. In Auckland, June output is 28% of the January peak. In Christchurch it is 18%, and in Dunedin just 16%. The further south, the bigger the seasonal swing.

Does NZ get enough sun for solar to be worth it?

Yes. NZ receives about 4 kWh/m² per day, comparable to southern France. Auckland produces 95% of what Melbourne generates, and NZ's cheapest city (Invercargill) still matches London. Solar payback periods in NZ are typically 5-7 years.

What is the difference between sunshine hours and solar yield?

Sunshine hours count the time the sun is visible. Solar yield (kWh/kWp) measures actual energy production, which also depends on sun angle, air clarity, temperature, and cloud type. Blenheim has the most sunshine hours (2,521) but ranks third for yield because its lower sun angle reduces irradiance per hour.