Time-of-use (TOU) electricity tariffs charge different rates depending on when you use power — with peak periods costing as much as 55c/kWh and off-peak periods as low as 15c/kWh. For Australian households with a home battery, this price spread is an opportunity to dramatically cut electricity costs by charging the battery overnight at cheap rates and discharging it during expensive peak periods. Here's exactly how the maths works — and when it makes financial sense.
What Is a Time-of-Use Tariff?
A time-of-use tariff splits the day into pricing periods where the cost of electricity varies. In most Australian states, there are typically three periods:
| Period | Typical Hours | Typical Rate |
|---|---|---|
| Peak | 3pm–9pm weekdays | 40–55c/kWh |
| Shoulder | 7am–3pm, 9pm–10pm | 25–32c/kWh |
| Off-Peak | 10pm–7am, weekends | 14–18c/kWh |
TOU tariffs aren't automatically better than flat-rate plans — they reward you for shifting usage away from peak periods, and punish you if you can't. This is exactly where a home battery shines.
How Batteries Interact With Time-of-Use Tariffs
A smart home battery system can be programmed to exploit TOU pricing in two distinct ways:
- Solar arbitrage: Store excess solar generation during the day (shoulder rates) and discharge during the evening peak (40–55c/kWh) to avoid peak charges.
- Grid arbitrage: In states where off-peak rates are very low (14–18c/kWh), charge the battery from the grid overnight and discharge during peak periods — essentially buying cheap and using expensive.
Most quality battery systems (Tesla Powerwall 3, BYD Battery-Box, Alpha ESS) support scheduled charging modes that can be set via an app, automatically aligned with your tariff's off-peak windows.
The Maths: How Much Can You Save?
Let's model a 10kWh battery with a solar system in New South Wales, where TOU tariffs are common and peak rates reach 50c/kWh:
| Scenario | Daily Saving | Annual Saving |
|---|---|---|
| Solar arbitrage only (no battery) | $0 (exports at 5–8c FiT) | $0 from storage |
| Battery stores solar, discharges in peak | $2.50–$4.00 | $900–$1,460 |
| Grid arbitrage (off-peak charge, peak discharge) | $1.50–$2.50 | $550–$910 |
| Combined solar + grid arbitrage | $3.50–$5.50 | $1,275–$2,000 |
At a 10kWh battery cost of $10,000–$14,000 installed, the solar arbitrage scenario alone gives a payback period of 7–15 years. Add grid arbitrage savings and the payback compresses to 6–10 years — approaching the edge of financial viability for many households.
Which States Have the Best TOU + Battery Savings?
The value of combining batteries with TOU tariffs varies significantly by state, depending on peak-to-off-peak spreads and solar generation:
| State | Peak Rate | Off-Peak Rate | Spread | Battery TOU Opportunity |
|---|---|---|---|---|
| New South Wales | 48–52c | 14–16c | 34–38c | Excellent |
| South Australia | 45–55c | 15–18c | 30–37c | Excellent |
| Victoria | 38–44c | 14–18c | 24–30c | Good |
| Queensland | 35–42c | 18–22c | 17–20c | Moderate |
| Western Australia | 35–40c | 17–20c | 18–20c | Moderate |
| ACT | 32–38c | 16–20c | 16–18c | Lower |
Is TOU + Battery Better Than a Flat-Rate Tariff + Battery?
This depends entirely on your household's peak usage patterns. A household that uses most of its electricity in the morning and daytime may find that a flat-rate tariff + solar + battery outperforms TOU, because they're naturally avoiding peak periods without the tariff structure pushing them.
Conversely, households with high evening usage — cooking dinner, running the dishwasher, charging an EV, and watching TV — are prime candidates for TOU + battery. The battery ensures peak-time usage is sourced from stored solar or cheap overnight grid power rather than expensive peak-rate electricity.
The key test: compare your actual evening usage (5pm–9pm) as a percentage of your total daily usage. If it exceeds 40%, TOU + battery is likely to deliver meaningful savings over a flat rate.
Amber Electric and Dynamic Tariffs
Alongside TOU, network-side demand tariffs are becoming more common and interact differently with battery dispatch. An emerging category beyond standard TOU is dynamic pricing, offered by retailers like Amber Electric. Dynamic tariffs pass through the wholesale market spot price in real time — which means prices can drop to nearly zero (or even go negative) during periods of high solar generation, and spike during extreme heat events when everyone runs air conditioning.
For battery owners on dynamic tariffs, smart battery software can automatically charge when prices go negative and discharge during price spikes — potentially earning hundreds of dollars extra per year compared to standard TOU arbitrage. This is the frontier of home battery optimisation in Australia, and it's rapidly becoming more accessible.
Work Out If a Battery Makes Sense for Your Tariff
The right combination of battery size, tariff type, and solar system depends on your specific usage profile and state. Use our Battery Payback Calculator to model your household's situation — including TOU tariff inputs — and see exactly how long it takes for a battery to pay for itself under different scenarios.