Choosing between time-of-use (TOU) tariffs and a flat import rate can greatly affect solar savings and payback. The best option depends on your household’s energy use patterns, solar export, and retailer plan details.
Key Definitions
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TOU (Time-of-Use Import): Different import rates for peak, shoulder, and off-peak hours.
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Flat Import: A single import rate, regardless of time.
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Self-consumption: Using your own solar power directly.
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Export FiT: Payment per kWh sent back to the grid.
Worked Examples
Example 1: Evening-Heavy Household
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Plan A (Flat): 30c/kWh import, 9c FiT.
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Plan B (TOU): 45c peak (3–9pm), 24c shoulder, 18c off-peak, 9c FiT.
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Usage: 12 kWh at night, 6 kWh daytime, exports 8 kWh/day.
Bill Impact:
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Flat: 18 × 30c = $5.40 – (8 × 9c = $0.72 credit) → $4.68 net/day.
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TOU: 12 × 45c = $5.40 + 6 × 24c = $1.44 – (8 × 9c = $0.72) → $6.12 net/day.
Winner: Flat rate (better for evening users).
Example 2: Daytime-Heavy Household
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Same tariffs as above.
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Usage: 14 kWh daytime, 4 kWh evening, exports 10 kWh/day.
Bill Impact:
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Flat: 18 × 30c = $5.40 – (10 × 9c = $0.90) → $4.50 net/day.
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TOU: 4 × 45c = $1.80 + 14 × 24c = $3.36 – (10 × 9c = $0.90) → $4.26 net/day.
Winner: TOU (suits households using power while solar is generating).
Example 3: EV Owner (Charging Overnight)
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Usage: 10 kWh overnight charging at off-peak.
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TOU off-peak: 18c vs flat: 30c.
Bill Impact: EV charging at TOU saves $1.20 per charge cycle compared to flat.
Winner: TOU for EV/night-time charging.
FAQs
Q: Is TOU always cheaper?
No. It depends on when you use energy. Evening-heavy households often pay more on TOU.
Q: Can solar exports offset peak costs?
Only if you shift enough daytime usage or have battery storage.
Q: Should EV owners prefer TOU?
Yes, if off-peak charging is available and fits your schedule.
Conclusion
The right choice between TOU and flat import depends on lifestyle. Households with heavy evening use may prefer flat, while daytime users and EV owners can benefit from TOU.
Explore your options with: