How NZ home solar actually pays for itself

Home solar in New Zealand pays back, on average, in seven to eleven years — meaningfully faster in Northland and Auckland, meaningfully slower in Dunedin. After payback, the system continues producing power for another fifteen to twenty years, almost entirely free. That is the headline. The interesting bit is the assumptions underneath, because changing any of them by ten percent shifts the payback year by a full year or more.

What an average install costs in 2026

A 6 kW grid-tied system — roughly fifteen panels, one inverter, no battery — sits between $14,000 and $19,000 installed and commissioned, GST included. A 10 kW system runs $20,000 to $26,000 in the same configuration. Installing a battery adds $9,000 to $16,000 depending on capacity. These are NZ-realistic 2026 numbers, drawn from quotes our directory installers have shared with us.

What it saves you per year

Two things matter for the savings calculation: how much electricity you currently buy, and how much of your solar generation you use directly versus export back to the grid.

• Self-consumed solar offsets your retail electricity rate — typically 28–35 c/kWh in NZ depending on retailer and region.
• Exported solar earns the buyback rate — typically 8–17 c/kWh in 2026 depending on retailer (Octopus, Flick, Meridian and Contact pay near the top; some legacy plans pay only 7 c).
• The split between self-consumed and exported depends entirely on when the household uses power: at midday you're self-consuming, in the evening you're buying back from the grid at full retail.

Why the calculator's numbers are deliberately rough

Our calculator uses regional average sun-hours (Auckland 5.5, Wellington 4.6, etc.) and a system efficiency of around 78% to convert kW of installed capacity to annual kWh generated. We assume 50% of that is self-consumed at retail rates and 50% is exported at buyback rates — an industry middle-ground that is realistic for a working-from-home or family household.

That set of assumptions will be wrong, in either direction, for any specific home. A retired couple home all day with an electric car charging at midday will self-consume more than 50% and pay back faster than the calculator suggests. An evening-only commuter household will self-consume less than 30% and pay back slower. The calculator gives you the middle of the range; an installer's site visit gives you yours.

What changes the answer most

• Retail electricity price: a 10% retail rise shaves about a year off payback. Real NZ retail prices are rising 4–6% a year on average, which is why solar payback gets shorter the longer you wait.
• Roof orientation: north-facing pitches between 20° and 35° are optimal in NZ. East/west losses are around 10–15%; south-facing roofs lose 25–35% and rarely pay back without a battery.
• Shading: even partial shading on one panel can drop a string's output by 30%. Microinverters or DC optimisers fix this — at 5–10% extra cost.
• Battery economics: batteries roughly double system payback time at current prices. They make sense for outage tolerance, time-of-use plan optimisation, or future EV charging — not for raw economic payback in 2026.

The honest version

If you are home during the day, on a north-facing roof, in Northland, Auckland or the Bay of Plenty, the maths on a 6–10 kW grid-tied system is straightforward and good. If you are out commuting, on a south-facing roof, in Dunedin, the maths is genuinely marginal and you should run the numbers carefully before you commit. We built the calculator to make that distinction visible rather than hidden.