A battery doesn't generate a single extra kWh of solar — what it does is let you use power you've already generated at 8pm instead of 11am. Whether that's worth roughly $429/kWh installed comes down to one gap: the difference between what you'd pay for grid power at night, and what you're credited for exporting that same solar during the day.
The gap that makes batteries pay off
| Region | Retail tariff (avoided cost) | Feed-in tariff (foregone) | Arbitrage margin |
|---|---|---|---|
| NSW (incl. Queanbeyan) | ~34c/kWh | ~5c/kWh | ~29c/kWh |
| ACT (Canberra) | ~37c/kWh | ~6c/kWh | ~31c/kWh |
Every kWh you store and use yourself instead of exporting is worth roughly 29–31c to you, rather than the 5–6c you'd get for exporting it — sourced from the AER Default Market Offer, ICRC, IPART and Evoenergy network benchmarks for 2026–27, the same figures behind our savings calculator.
What batteries cost installed
Island Solar installs batteries at roughly $429/kWh, fitted the same way as our PV rate — from real recent job costs, not a promotional headline price.
| Battery size | Indicative cost | Typical fit |
|---|---|---|
| 5 kWh | $2,145 | Light evening usage top-up |
| 10 kWh | $4,290 | Most 3–4 person households |
| 13.5 kWh | $5,792 | Higher evening usage or partial blackout cover |
| 20 kWh | $8,580 | Larger homes, EV charging, most of the home on backup |
A worked payback example
A 10kWh battery in NSW: ~9kWh usable/day × 29c × 300 days ≈ $783/yr saved, against a $4,290 install cost — roughly a 5.5-year payback. In the ACT, the slightly wider tariff gap brings that closer to 5 years.
Interestingly, that payback period stays fairly consistent whether you install a 5kWh or a 20kWh battery, provided you actually use that much stored energy every evening. A 20kWh battery only pays off proportionally if your household genuinely draws down close to 18kWh overnight (running an EV charger, ducted heating/cooling, or heavy evening appliance use) — undersized usage against an oversized battery just stretches the payback out.
Not sure what size battery fits your home?
Our calculator models 5kWh, 10kWh, 13.5kWh and 20kWh options against your actual bill.
Blackout protection, not just bill savings
The financial case is only half the story for a lot of Canberra and Queanbeyan households — a correctly configured battery can keep essential circuits running through a grid outage, which is a genuine consideration for anyone with medical equipment, home offices, or a family that just doesn't want the fridge off for six hours during a storm. This is a separate conversation to the pure payback math and worth raising during your site inspection.
The emissions side
Self-consuming more of your own solar (rather than exporting it and drawing grid power back at night) also reduces reliance on grid electricity carrying a 0.64kg CO₂-e/kWh emissions factor (National Greenhouse Accounts Factors, 2025) — shared across the NSW/ACT grid, since it's the same physical network.
