Maximising Battery Value with Time-of-Use Tariffs
How Time-of-Use Changes the Equation
On a flat-rate tariff, a battery's value is simple: store cheap solar, use it instead of buying grid power at a constant rate.
Time-of-use (TOU) tariffs add a layer of complexity and opportunity. Power costs different amounts at different times, and a well-managed battery can exploit this differential.
Understanding Synergy's Time-of-Use Options
Midday Saver (A1 with Time Bands)
The most common TOU option for solar households:
| Period | Time | Rate (indicative) |
|--------|------|-------------------|
| Peak | 3pm - 9pm | ~45¢/kWh |
| Shoulder | 7am - 3pm, 9pm - 9am | ~32¢/kWh |
| Midday | 9am - 3pm | ~20¢/kWh |
Rates are indicative and change. Check Synergy for current rates.
The Value Opportunity
The spread between peak (45¢) and midday (20¢) is 25¢/kWh. Every kilowatt-hour you store during midday and use during peak saves you that 25¢ differential (minus efficiency losses of ~10%).
Net value per kWh shifted: ~22¢
For a 10kWh battery cycling once daily: ~$800/year just from the timing arbitrage.
Battery Strategy for TOU
Charging Phase (9am - 3pm)
During the midday low-rate period:
- Solar priority: Battery charges from solar first (free energy)
- Grid top-up: If solar is insufficient, consider grid charging at low midday rates
- Goal: Full battery by 3pm when peak period starts
Some batteries allow you to enable grid charging during specific windows. This ensures full charge even on cloudy days.
Discharge Phase (3pm - 9pm)
During the peak period:
- Prioritise battery: Draw from battery before grid
- Cover household load: Match discharge to consumption
- Consider export: If battery is full and household load is low, exporting at DEBS peak rates (10¢/kWh) may make sense
Evening/Overnight (9pm onwards)
After peak period ends:
- Battery can rest: Rates drop to shoulder/off-peak
- Grid import is acceptable: Much cheaper than peak
- Preserve for morning: Keep some charge for morning use before solar starts
Optimisation Strategies
Strategy 1: Conservative Peak Avoidance
Goal: Never import during peak period
Method: Fully charge battery, discharge only during 3-9pm
Risk: Lower - straightforward to implement
Savings: Good
Strategy 2: Aggressive Arbitrage
Goal: Maximise the rate differential
Method: Grid charge during midday if needed, discharge aggressively during peak
Risk: Higher - depends on accurate load prediction
Savings: Potentially better
Strategy 3: Weather-Adaptive
Goal: Adjust based on solar forecast
Method: Grid charge more on cloudy days, less on sunny days
Risk: Moderate - requires attention or smart automation
Savings: Optimised
Automation and Smart Features
Modern batteries offer features that help with TOU optimisation:
Time-Based Control
Set charging and discharging windows that align with rate periods.
Reserve Settings
Keep minimum charge for backup or morning use.
Solar Forecast Integration
Some systems adjust strategy based on weather forecasts.
Learn Mode
Advanced systems learn your consumption patterns and optimise automatically.
If your battery has these features, use them. Manual management is possible but tedious.
VPP Interaction
If you're enrolled in Synergy Battery Rewards:
- VPP events override your normal discharge strategy
- Events typically occur during peak period (when you'd be discharging anyway)
- You earn VPP rate (70¢/kWh) instead of saving peak rate (45¢/kWh)
Net effect: VPP events are actually more valuable than normal peak-period use. Don't try to avoid them.
DEBS Export Optimisation
The Distributed Energy Buyback Scheme pays:
- 10¢/kWh during 3-9pm (peak export)
- 2¢/kWh other times
When to Export:
If your battery is full and household load is low during peak period, exporting earns 10¢/kWh. This is less valuable than avoiding a 45¢/kWh import, but more valuable than just sitting there.
Strategic Discharge:
Some households with large batteries and low evening consumption deliberately export during peak export hours. The economics depend on your specific situation.
Common Mistakes
Mistake 1: Not Using Time Windows
Just setting the battery to "self-consumption" mode misses the TOU opportunity. Configure time-based control.
Mistake 2: Over-Discharging Before Peak Ends
Running the battery empty at 7pm leaves you buying peak-rate power for the last two hours. Better to pace discharge across the full peak period.
Mistake 3: Ignoring Cloudy Day Reality
On a cloudy day, the battery may not fully charge from solar. Having grid charging enabled during midday periods ensures you're still covered for peak.
Mistake 4: Set and Forget
TOU rates change. Seasons change. Consumption patterns change. Review your settings periodically to ensure they're still optimal.
Is TOU Right for You?
Time-of-use tariffs work best when:
- You have a battery to shift consumption
- Your peak period consumption is significant
- You can be somewhat flexible about when you use power
They may not work well when:
- Most of your consumption is during peak period with no flexibility
- Your consumption is already very low
- You don't have solar or battery to manage timing
Run the numbers before switching. Synergy's comparison tools can help estimate impact.
Example Savings Calculation
Assumptions:
- 12kWh battery, 90% efficiency
- 10kWh usable daily cycle
- 300 days/year of meaningful TOU benefit
Calculation:
- Without TOU: Save import rate (~32¢) = 10 × 0.32 × 300 = $960/year
- With TOU: Save peak rate (~45¢) = 10 × 0.45 × 300 = $1,350/year
Additional TOU benefit: ~$390/year
This is rough - actual benefit depends on your specific consumption, rates, and how well you optimise.
Getting Started
- Check current tariff: Understand what you're on now
- Review consumption: When do you use the most power?
- Model the switch: Use Synergy's tools or ask for help
- Configure battery: Set up time-based controls
- Monitor results: Track for a few months, adjust as needed
Summary
Time-of-use tariffs add value for battery owners who are willing to optimise their charging and discharging. The additional savings of $300-500/year are meaningful and compound over the battery's lifetime.
The key is proper configuration - set up your time windows, enable appropriate automation, and review occasionally.
Not sure where to start?
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