Battery payback in Perth: the honest numbers for 2026

A home battery generates savings in two ways: it lets you use solar electricity you'd otherwise export (at 2–10c/kWh) instead of buying grid power in the evening (at 33.26c/kWh), and it provides grid independence during outages. The financial return depends almost entirely on the first mechanism — the import-export spread.

Here's how to calculate whether a battery pays back in your situation.

The fundamental maths

Every kWh stored in the battery and used in the evening saves: 33.26c (grid import avoided) − 2c (DEBS off-peak export foregone) = 31.26c net saving per kWh

If the battery self-discharges or there's inverter inefficiency, the effective saving is closer to 28–30c/kWh after losses.

For a battery that cycles once per day: A 10kWh usable battery (80% DoD, 12.5kWh nameplate) cycling daily at 80% DoD provides approximately 8kWh of useful daily discharge.

Annual savings = 8 kWh/day × 365 days × $0.30/kWh = approximately $876/year

At a post-rebate battery cost of $9,000–$11,000 (10kWh usable, after WA Battery Scheme $1,300 rebate):

• Payback = $10,000 ÷ $876 = approximately 11.4 years

This is the baseline. Multiple factors move this up or down.

What improves battery payback

High self-discharge rate (lots of evening grid import)

A household that currently imports significant power after solar stops is the ideal battery customer. If you're importing 12–15 kWh/night at 33.26c (a $4–$5 nightly grid bill), a battery that eliminates this saves correspondingly more.

Midday Saver tariff arbitrage

On Synergy's Midday Saver:

• Super off-peak (9am–3pm): 8.85c/kWh
• Peak (3pm–9pm): 55.33c/kWh
• Off-peak (9pm–9am): 24.34c/kWh

The battery charges during super off-peak (solar or cheap grid backup) and discharges during peak (3pm–9pm window). Saving at 55.33c/kWh instead of A1's 33.26c makes each cycle worth significantly more:

55.33c − 2c DEBS = 53.33c net saving per kWh discharged during peak

At Midday Saver rates: Annual savings = 8 kWh × 365 × $0.50 = approximately $1,460/year

Payback at Midday Saver: $10,000 ÷ $1,460 = approximately 6.8 years

Midday Saver is the strongest argument for battery economics in Perth. It shifts from A1-tariff savings to peak-rate arbitrage — a substantial difference.

What hurts battery payback

Low cycling rate

If you're away for extended periods, or your household already has very low evening consumption, the battery doesn't cycle enough to earn back its cost. A battery cycling only 200 days per year (illness, holiday) instead of 330+ saves proportionally less.

Small import-export spread

On standard A1 tariff (33.26c import, 2c off-peak export), the spread is 31.26c. If future electricity prices fall significantly (unlikely in the short term given WA network costs), the spread shrinks.

Battery degradation

After 10 years, most LFP batteries retain 70–80% of original capacity. A battery providing 8kWh usable at year 1 provides 5.6–6.4kWh usable at year 10 — reducing savings. The degradation curve means later years of the payback period generate less than earlier years.

Worked example: 4-person Perth household on Midday Saver

| Assumption | Value | |---|---| | Battery: 13.5kWh Tesla Powerwall 2 (installed, post-rebate) | $12,000 | | Usable daily discharge (evening) | 10 kWh | | Tariff: Midday Saver (save at peak 55.33c vs export at 2c DEBS) | ~53c net/kWh | | Annual days cycling | 320 days | | Annual savings | 10 kWh × 320 × $0.53 = $1,696 | | Simple payback | $12,000 ÷ $1,696 = 7.1 years |

On standard A1 tariff:

| Assumption | Value | |---|---| | Net saving per kWh | 31.26c | | Annual savings | 10 kWh × 320 × $0.31 = $992 | | Simple payback | $12,000 ÷ $992 = 12.1 years |

The tariff choice has a larger impact on payback than almost any other factor within the household's control.

Battery payback vs solar payback

Solar typically pays back in 3–6 years in Perth. Battery pays back in 7–13 years (depending on tariff).

This doesn't make battery a poor choice — it still generates a positive return over its 10–15 year life — but it does mean:

• Solar first, battery second is almost always the right order
• Optimising your tariff (Midday Saver for battery households) is as important as choosing the right battery
• For households near the end of their payback timeline decision, the non-financial value (backup, grid independence) may tip the decision

Calculations based on Synergy A1 rate 33.26c/kWh and Midday Saver peak rate 55.33c/kWh, effective 1 July 2026. DEBS off-peak export rate 2c/kWh. Battery costs are post-rebate estimates and vary by brand and installer. Results are indicative — your savings depend on your actual consumption pattern.