Solar Battery Payback Calculator NZ

This calculator works out how many years it takes a home solar battery to pay for itself in New Zealand, so you can judge whether adding storage to your solar system stacks up financially. Without a battery, any solar power you generate but do not use straight away gets exported to the grid at a low buy-back rate, then bought back in the evening at the much higher retail price. A battery closes that gap by storing your surplus solar for later use in your own home. You enter the installed cost of the battery, how many kilowatt-hours a year it lets you self-use instead of exporting, your retail power price per kWh, and the export buy-back rate per kWh. The calculator returns the battery payback period in years, the dollar saving per year, and the saving per kWh shifted from export to self-use. Use it to compare battery quotes against your own power and export rates, and to see how sensitive the payback is to those prices, since a bigger gap between what you pay and what you are paid for export means a faster payback. It is also worth weighing the payback period against the battery's warranty, typically around ten years, and remembering that backup power during an outage has value beyond the dollar saving. Figures are indicative estimates only, based on the rates and usage you enter.

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26.7 years
battery payback period
Saving per year$450
Saving per kWh shifted$0.18

The saving is the gap between the power price and the export buy-back rate, on the energy the battery shifts to evening use. Compare the payback with the battery's warranty (often around 10 years). Backup power in outages is a benefit beyond the dollars. Estimate only.

How it works

The calculator finds the saving per kWh as the difference between your power price and the export buy-back rate, since each kWh the battery lets you self-use both avoids buying at retail and would otherwise only have earned the low export rate. It multiplies that by the self-used kWh a year for the annual saving, then divides the battery cost by it for the payback period.

Worked example

Self-using 2,500 kWh a year, with a 30 cent power price and a 12 cent export rate, the saving is 18 cents a kWh, about $450 a year. A $12,000 battery would take around 27 years to pay back on that alone, which shows why battery economics are often marginal in NZ today.

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Frequently asked questions

Is a home battery worth it with solar?

A battery lets you use more of your own solar power in the evening instead of buying from the grid, and avoids exporting it for a low buy-back rate. The saving is the gap between the retail power price and the export rate, on the energy you shift, weighed against the battery cost.

How is the battery saving calculated?

It is the energy the battery lets you self-use each year, multiplied by the difference between what you would pay to buy power and what you would get for exporting it. The bigger that gap, the faster the battery pays back.

Do batteries last long enough to pay back?

Batteries are warrantied for around 10 years. If the payback is well under that, it stacks up; if it is close to or beyond the battery life, the economics are marginal, though backup power has value in outages.