Introduction
Choosing between a time-of-use (TOU) import tariff and a flat import tariff can make a big difference in your electricity bill. For solar households, the right choice depends on when you use energy, how much you export, and your retailer’s feed-in tariff (FiT). This guide explains both tariff types, shows worked examples, and links to calculators so you can model your own savings.
Key Definitions
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Flat import tariff: A single rate for every kWh imported, regardless of the time of day.
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TOU import tariff: Different import rates depending on the time (peak, shoulder, off-peak).
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FiT (feed-in tariff): Credit you earn for each kWh exported.
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Net bill: Your final bill after import charges and export credits are balanced.
Check Retailer Rates to see both TOU and flat options in your state.
Worked Example 1 — Flat vs TOU on a 20 kWh/day Household
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Usage: 20 kWh/day
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Solar generation: 15 kWh/day
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Self-consumption: 10 kWh/day
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Exports: 5 kWh/day
Flat import:
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Import = 10 kWh/day × 28c = $2.80/day
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Export credit = 5 × 8c = 40c/day
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Net = $2.40/day
TOU import (40c peak, 20c off-peak, 28c shoulder):
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6 kWh peak × 40c = $2.40
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4 kWh off-peak × 20c = $0.80
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Export credit = 40c
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Net = $2.80/day
In this case, the flat tariff is cheaper.
Worked Example 2 — Solar Household with Evening Usage
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Usage: 18 kWh/day
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Solar generation: 12 kWh/day
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Self-consumption: 9 kWh/day
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Exports: 3 kWh/day
Flat import:
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Import = 9 kWh × 28c = $2.52/day
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Export credit = 3 × 8c = 24c/day
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Net = $2.28/day
TOU import:
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3 kWh peak × 40c = $1.20
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6 kWh off-peak × 20c = $1.20
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Export credit = 24c
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Net = $2.16/day
Here, TOU wins because much of the import happens off-peak.
Worked Example 3 — Seasonal Shifts
In summer, solar covers more usage, reducing imports (flat and TOU differences shrink).
In winter, evening imports increase, making TOU potentially riskier unless you shift loads (e.g., run appliances in off-peak).
Use the Postcode Estimator to model your city’s seasonal output.
Key Takeaways
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Flat tariffs are safer for households with steady or peak-heavy evening use.
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TOU tariffs benefit those who can shift demand to off-peak times (e.g., EV charging overnight).
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Always weigh both FiT rates and supply charges, not just import pricing.
Run your own bill comparisons using the FiT Savings Calculator and monitor changes with the Rate Change Tracker.
FAQs
Q1. Is TOU always cheaper than flat tariffs?
No. TOU only pays off if you can use more power during off-peak hours or have storage like a battery.
Q2. Can solar exports offset peak imports?
Partly — but exports usually happen midday, while peak rates apply in the evening. A battery helps bridge this gap.
Q3. Does TOU FiT also exist?
Yes. Some retailers offer time-varying FiTs where exports in the evening get higher credits. Compare at Compare FiT by State.
Q4. What’s the role of supply charges?
Even if your TOU import rate looks cheaper, a higher daily supply charge can wipe out the gains.
Conclusion
Modeling TOU vs flat tariffs with your actual usage pattern is the only way to know which plan saves more. Inverter and smart meter data, combined with calculators and retailer comparisons, give you a clear picture. Test your numbers before switching to avoid bill surprises.