EV + Home Battery in Perth: Making Them Work Together
The Growing Complexity
More Perth households now have three energy systems to manage: solar panels, a home battery, and an electric vehicle. Each has its own charging requirements, and they all compete for the same solar generation.
Done well, the integration can maximise your solar investment. Done poorly, you end up with a home battery that never charges because the EV takes all the solar.
Understanding the Energy Flow
On a typical day, your solar panels generate electricity. That electricity can go to:
- Immediate household consumption (always first priority)
- Home battery charging
- EV charging
- Grid export
The challenge is that both your home battery and your EV want to charge from solar during the same hours. A 6.6kW solar system generating 5kW at midday can't simultaneously charge a 7kW EV charger AND a home battery.
The Sizing Question
Solar Array
With an EV in the picture, most households need more solar than the traditional 6.6kW. Consider:
- Average household consumption: 15-25 kWh/day
- Home battery: 10-13 kWh to charge daily
- EV: 10-15 kWh/day for typical driving (40-60km)
That's 35-50+ kWh of daily demand. Even accounting for some grid charging and imperfect timing, a 10kW+ solar array makes sense for households with EVs and batteries.
Home Battery
The home battery serves your evening consumption - after the sun sets and before you plug in the EV overnight. A 10-13 kWh battery typically covers evening use for most households.
Don't over-size the home battery thinking you'll store energy for the EV. Home-to-EV energy transfer is rarely efficient or practical (though some systems are starting to support it).
EV Charger
A 7kW single-phase charger is typical for Perth homes. Three-phase 22kW chargers exist but require appropriate electrical infrastructure.
The charger power matters for how quickly you can capture solar:
- 7kW charger in 4 hours of good sun: ~28 kWh
- 3.7kW charger in 4 hours: ~15 kWh
Higher power chargers capture more solar when conditions allow.
Charging Priority Strategies
Strategy 1: EV Charges Overnight
The simplest approach: EV charges overnight from the grid at off-peak rates (if you have a time-of-use tariff). Solar charges the home battery during the day.
Pros:
- No competition for solar
- Home battery always fully charged for evening
- Simple to implement
Cons:
- EV uses grid power rather than solar
- Only works well with time-of-use tariffs
Strategy 2: EV Has Solar Priority
Set the EV to charge during midday hours. Home battery charges with whatever solar remains.
Pros:
- Maximises solar self-consumption
- Minimises grid imports for EV
Cons:
- Home battery may not fully charge
- Requires EV to be home during the day
Strategy 3: Dynamic Scheduling
Some systems can dynamically allocate solar between home battery and EV based on state of charge, time of day, and forecast conditions.
Pros:
- Optimises across the whole system
- Adapts to varying conditions
Cons:
- Requires compatible equipment
- More complex setup
Equipment Considerations
Integrated Systems
Some manufacturers offer integrated solutions:
Tesla: Powerwall and Wall Connector share a common app and can coordinate charging schedules. The system can prioritise home battery, EV, or balance between them.
Sungrow/EVSE combinations: Some Sungrow hybrid inverters integrate with compatible EV chargers for coordinated control.
Separate Systems
If your home battery and EV charger are from different manufacturers, coordination is manual:
- Set EV charging schedules based on typical solar generation windows
- Adjust seasonally as generation patterns change
- Monitor and refine based on actual experience
Tariff Optimisation
Perth's time-of-use tariffs create opportunities:
Synergy Time of Use (Midday Saver)
- Peak (3pm-9pm): Highest rates - use stored battery energy
- Midday (9am-3pm): Low rates - charge EV if home
- Off-peak (9pm-7am): Lower rates - charge EV overnight
Strategy
- Home battery charges during midday (low rates)
- Battery powers evening consumption (avoids peak rates)
- EV charges either during midday (if home) or overnight (off-peak)
This approach minimises cost while maximising solar use.
VPP Considerations
If you're enrolled in Synergy Battery Rewards:
- VPP events discharge your home battery during peak periods
- This may affect your evening consumption coverage
- EV charging schedules should account for possible VPP events
Typically, VPP events don't significantly impact EV charging since they occur during peak hours when most EVs are connected but not actively charging.
Practical Recommendations
If You're Adding an EV to Existing Solar + Battery:
- Review your solar generation vs new total demand
- Consider solar upgrades if undersized
- Set up charging schedules that avoid competition
- Monitor for the first few months and adjust
If You're Planning All Three Together:
- Size solar for total household + battery + EV needs (10kW+ typical)
- Choose a home battery that integrates well with your planned EV charger
- Consider a single-ecosystem approach (e.g., all Tesla) for easier integration
- Plan electrical capacity for future expansion
If You Have an EV and Are Adding a Battery:
- Assess how much solar is typically available after EV charging
- Size the battery for realistic available generation
- Consider whether your solar needs upgrading first
The Financial Picture
Adding complexity (more equipment, more charging to manage) should add value. The financial case works when:
- Solar generation exceeds total demand (battery + EV + home)
- Equipment costs are offset by fuel/electricity savings
- Your lifestyle allows for flexible charging times
EVs typically save $1,500-2,500/year compared to petrol vehicles (depending on driving distance and petrol prices). Home batteries save $800-1,500/year for typical households. Solar saves $1,000-2,000/year.
Together, the savings can be substantial - but the upfront investment is significant. Run the numbers for your specific situation.
Common Mistakes to Avoid
- Under-sizing solar: Adding an EV to 6.6kW solar often leaves both EV and battery fighting for limited generation
- Ignoring winter: EV charging needs don't disappear in winter, but solar generation drops significantly
- No charging schedule: Just plugging in the EV whenever depletes solar that could charge the home battery
- Over-optimising: Perfect is the enemy of good. A simple schedule that mostly works beats a complex system that requires constant management
Summary
EV + battery integration works best when:
- Solar is adequately sized for combined demand
- Charging schedules avoid direct competition
- Equipment allows some coordination (even if manual)
- Expectations are realistic about seasonal variation
Most Perth households can make this combination work with thoughtful planning. Start simple, monitor results, and refine over time.
Not sure where to start?
Six questions, two minutes. We'll match you with CEC-accredited Perth installers who quote based on your actual usage.