Key takeaways
- Grid-tied solar only: 6 to 8 years payback. With a battery: 10 to 14. Battery added later: 15 or more (Solar Scout, 2026).
- Average installed battery cost: about $1,219 per kWh.
- A battery earns its keep when you use lots of power after dark, want outage backup, or get a low buy-back rate.
- A standard grid-tied system switches off in a power cut; only a battery with backup keeps the lights on.
What's the difference between grid-tied solar and a battery system?
A grid-tied system uses solar in your home as it's generated and exports the rest to the grid for a buy-back rate. A battery stores the surplus so you can use it in the evening instead of exporting it for 8c to 24c and buying power back at night for around 40c.
How much does a solar battery cost in NZ?
About $1,219 per kWh of storage installed on average in 2026 (Solar Scout). Prices vary a lot by brand and size: of the five rows below, BYD and Sungrow start at $800 per kWh, Enphase at $1,200 or more, and a single Powerwall 3 is $1,407 – $1,778 per kWh.
| Battery | Capacity | Installed price | Per kWh |
|---|---|---|---|
| Tesla Powerwall 3 | 13.5 kWh | $19,000 – $24,000 | $1,407 – $1,778 |
| Powerwall 3 expansion | +13.5 kWh | $5,900 – $6,000 | $437 – $444 |
| BYD Battery-Box | 5 – 12.8 kWh | $8,000 – $20,000+ | $800 – $1,200 |
| Sungrow | Various | Competitive | $800 – $1,000 |
| Enphase IQ Battery | 5 / 10 kWh | Premium | $1,200+ |
When does a battery pay?
When a large share of your use is after dark, your buy-back rate is low, or you place a real value on backup power. For a household out all day that exports most of its solar, a battery turns 8c to 24c exports into savings at around 40c, but the extra $8,000 to $24,000 still stretches payback.
- High evening use: cooking, heating, EV charging overnight
- Low buy-back rate from your retailer
- Frequent outages, or someone at home who needs power for medical equipment
- You already use most of your solar in the day: a battery adds little
Should I add a battery now or later?
If you're unsure, start without one and choose a hybrid-ready inverter so a battery can be added later. Solar Scout notes retrofitting a battery to existing solar has the longest payback, 15 years or more, so if you know you want one, installing both together is cheaper.
Why don't you push batteries?
A Powerwall 3 alone costs more than a typical 6.6kW solar system, and the payback maths usually doesn't support one for a typical home. We price a battery as an add-on, show its payback separately, and only recommend it when your answers point to heavy evening use or a need for backup.
Frequently asked questions
Is a Tesla Powerwall worth it in NZ?
At $19,000 to $24,000 installed for 13.5 kWh (Solar Scout, 2026), only for households with heavy evening use or a strong need for backup. Payback on solar plus battery is typically 10 to 14 years.
Does solar work in a power cut without a battery?
No. Grid-tied inverters shut down during an outage so they don't feed power into lines being worked on.
How big a battery do I need?
Enough to cover your evening and overnight use. Your retailer's app shows hourly use; the evening total is a sensible starting size.
Can I add a battery later?
Yes, particularly with a hybrid-ready inverter, but Solar Scout puts retrofit payback at 15 years or more.
How long do solar batteries last?
EECA's minimum warranty to look for on lithium-ion batteries is 10 years (EECA).
Sources
- Solar Scout, Solar battery storage NZ (updated 30 Aug 2026) (checked 30 Aug 2026)
- Solar Scout, Buy-back rates NZ (updated 31 Aug 2026) (checked 31 Aug 2026)
- Canstar NZ citing MBIE Quarterly Survey of Domestic Electricity Prices to 15 Feb 2026 (checked Feb 2026)
- EECA, Solar quotes and installation (checked Sept 2026)
General information, not financial advice. Prices and rates change; each figure shows where it came from and when it was checked.