Battery vs grid-tied — which one pays back in NZ?

Adding a battery to a home solar install in NZ roughly doubles the payback period. That is the awkward truth that solar showrooms tend to bury under the slide deck about 'energy independence'. There are good reasons to add a battery anyway — but raw economic payback is currently not one of them. Here is the actual decision.

What a battery costs in 2026

A useful residential battery — 10 to 15 kWh — costs $9,000 to $16,000 installed in NZ in 2026 once the inverter / hybrid configuration and commissioning are accounted for. The Tesla Powerwall 3 sits near the top of that range; Sungrow, BYD and a handful of NZ-assembled systems sit in the middle. Cheaper batteries exist but the warranty and cycle-life numbers usually do not justify the saving.

What a battery earns you per year

A battery earns the gap between your retail electricity price (around 30 c/kWh) and your export buyback rate (around 12 c/kWh). On 5 kWh of energy time-shifted per day, that is roughly $325 a year. Add the value of avoided outage minutes — modest, in suburban NZ — and you get to maybe $400 a year of real value.

$10,000 of battery to earn $400 a year is a 25-year payback, which is longer than the battery's expected service life. That is the basic problem.

When a battery is genuinely the right call

• You are on a long rural feeder that drops out in storms — outage value is real and meaningful, not theoretical.
• You are on a time-of-use retail plan with a sharp peak/off-peak gap, where battery time-shifting earns 18–22 c/kWh of arbitrage rather than the standard 18 c.
• You are planning to add an EV that will charge in evening hours, after solar generation has stopped — the battery becomes the EV's daytime solar buffer.
• You want true grid-independence (off-grid) for ideological reasons and you accept the cost premium that comes with it — fine, but be honest about it being a values choice, not an economic one.

When grid-tied alone is the right call

• You are in town on a reliable network — outages are rare and short.
• You're on a flat retail electricity plan, not time-of-use.
• You are home during the day enough to self-consume 40–60% of generation directly.
• You'd rather pay back the system in 7–10 years than 14–20.

What we recommend

Get a written quote for grid-tied alone, and a separate written quote for grid-tied plus battery. Run both numbers through the calculator on the home page. If the battery is something you want for outage tolerance or future EV plans, the price premium is real but knowable. If you're being talked into one because it 'pays for itself faster' — that is mostly not true in NZ in 2026, and the maths above is why.