Solar & battery comparison
Solar on its own?
Or solar with storage?
Two different investments. Understand what a battery adds, the extra investment and trade-offs, and which goals it can help address.
Is a solar battery worth adding?
A battery may help when you have surplus daytime generation and useful demand later, or when a specifically designed backup supply matters to you. If you already use most solar as it is produced, storage may add less value. Compare the additional cost and operating conditions separately from the solar panels.
| Question | Solar only | Solar + battery |
|---|---|---|
| When can I use generation? | As it is generated during daylight. | During daylight and later, if stored energy is available. |
| What happens to surplus? | May be exported under your connection and retailer plan. | May charge storage first, with remaining surplus exported where allowed. |
| Will it provide backup? | A standard grid-connected system shuts down in an outage. | Only with backup-capable equipment, isolation and an agreed circuit design. |
| What else must I compare? | Generation, on-site use, tariff and installation scope. | Added cost, usable capacity, power, efficiency, compatibility and warranty conditions. |
Remember the electricity you could have exported
Storing surplus solar has an opportunity cost: that energy might otherwise earn an export credit. Compare the value of electricity delivered later with the export value you give up, as well as battery losses and costs.
A simple example, not a forecast
Suppose you send 5 kWh of surplus solar into storage, recover 90% for later use, avoid imports at 30 NZ cents/kWh, and give up exports at 10 NZ cents/kWh:
5 × 0.90 × $0.30 − 5 × $0.10 = $0.85
That is an illustrative $0.85 energy-value difference for that cycle. It is not a daily or annual saving claim. All figures are hypothetical; the example excludes purchase cost, finance, degradation, standby use and other operating effects.
How much backup runtime will I get?
Runtime depends on the energy available at the start of the outage and the loads connected to backup. High simultaneous power can exceed a system’s output even when energy remains. Ask for a list of supported circuits and operating limits rather than assuming the whole property will stay powered.
Can I add a battery later?
Sometimes. Check the existing inverter, installation layout and product compatibility before treating a system as battery-ready. Future product availability and the cost of a retrofit cannot be assumed.
A useful decision sequence
- Model solar-only against your actual electricity use.
- Identify surplus generation and useful demand at other times.
- Value backup separately if resilience is a goal.
- Compare the battery’s added cost and its own written conditions.
- Test different import/export tariffs and lower-than-expected utilisation.
Independent guidance
Does every battery support backup?
No. Backup depends on the complete system and configuration. Confirm the inverter, switching/isolation design and agreed circuits in your proposal.
Does a battery always shorten solar payback?
No. A battery adds investment cost. Its financial value depends on tariffs, utilisation and operating conditions; resilience can be a separate reason to consider it.