Not all electricity costs the same. If you're on a time-of-use (TOU) tariff, you're paying different rates depending on the time of day. Understanding how this interacts with solar is the key to maximising your savings.
How Time-of-Use Tariffs Work
Most Australian states now offer (and some require) time-of-use metering. The structure varies by retailer and state, but the general pattern is:
- Peak: Typically 4pm–9pm weekdays. Rates often 35–55c/kWh — the most expensive electricity of the day.
- Shoulder: Mornings and weekends. Rates typically 25–35c/kWh.
- Off-peak: Late night/overnight. Rates typically 15–22c/kWh — cheapest electricity available.
The Problem: Solar Generates at the Wrong Time
Here's the mismatch. Solar generates electricity from roughly 8am–5pm, with peak output around midday. But the most expensive electricity (peak tariff) is 4pm–9pm — after most of your solar generation has already wound down.
On a flat-rate tariff, every kWh of solar self-consumed saves you the same amount. On a TOU tariff, a kWh consumed at midday from your panels saves you shoulder rates (25–35c). A kWh consumed at 6pm — after the sun has set — costs you peak rates (35–55c). The financial case for solar-only is slightly weaker on TOU if you have high evening electricity consumption.
The Solution: Shift Loads or Add a Battery
Load Shifting (Free, Just Requires Habit)
Move high-consumption tasks to solar hours: run the dishwasher at noon, not after dinner. Run the washing machine during the day. Set your hot water system to heat between 10am–3pm. Pre-cool or pre-heat your home during solar generation so you need less air conditioning during peak hours.
Effective load shifting can recover most of the TOU disadvantage without spending a dollar.
Battery Storage (Paid, More Complete Solution)
A battery charged during the day with solar, then discharged during the 4pm–9pm peak period, is perfectly designed for TOU tariffs. You're replacing 40–55c peak electricity with stored solar that cost you nothing to generate. This is where batteries make the strongest financial case — households on TOU tariffs with high evening consumption have significantly better battery payback periods than those on flat rates.
Should You Switch Tariffs?
If you currently have a flat-rate tariff and are adding solar without a battery, there's an argument for staying on a flat rate — you get consistent value per kWh self-consumed. If you're adding a battery, a TOU tariff often improves the total economics because the peak-period savings from battery discharge are higher.
Run the numbers for your specific usage pattern before switching. Your electricity retailer can model the comparison, or you can use GridBeater to understand your baseline consumption before making the call.
Understand what solar saves on your tariff → Upload your bill free at GridBeater