The 2026 reality: more WA households have an EV than expected
EV sales in WA more than tripled between 2023 and 2025. Perth's high garage-to-house ratio (most homes have private off-street parking) means home charging is the default. And once you're charging at home, the battery + EV combination becomes much more powerful than either alone.
Why EV households need bigger batteries
An EV adds roughly 6–9 kWh of nightly load if you charge at home daily. That's not optional - that's pure addition on top of your existing household consumption. A 10 kWh battery sized for non-EV households gets entirely consumed by the EV alone in a single night.
Recommended sizing if you have or plan an EV:
- One EV, daily charging: 13.5–16 kWh battery
- One EV, charged 3x/week: 10–13.5 kWh battery is fine
- Two EVs: 20 kWh minimum, ideally with smart load-balancing
Charge strategy: from grid, from solar, or from battery?
Three options once you have all three (grid + solar + battery + EV):
1. Charge directly from midday solar
This is the ideal scenario. Your EV charges from excess solar during 11am–3pm, your home battery charges from any remaining excess, and evening loads come from the home battery. The grid is barely touched.
Works best if at least one EV is at home during weekdays, or if you have a flexible work-from-home pattern.
2. Charge overnight from cheap off-peak rates
If both EVs leave the house daily, charging needs to happen overnight. Synergy's Smart Home Plan off-peak rate (typically 9pm–6am) is about 15c/kWh - half the standard daytime rate. Set the EV charger to start at 9pm. The home battery, separately, covers your 6pm–9pm peak.
3. Charge from the home battery (rare, usually suboptimal)
You can charge an EV directly from a home battery, but it's usually inefficient - you're round-tripping electricity through two batteries with stored losses both ways. Only makes sense if you've sized the home battery massively (20 kWh+) and grid charging is unavailable.
The smart EV charger question
A "dumb" 7 kW EV charger draws full power regardless of solar generation, grid prices or your home battery state. A smart charger (Fronius Wattpilot, Wallbox Pulsar Plus, Zappi, Tesla Wall Connector) integrates with your solar inverter and battery to dynamically charge only when conditions are right.
If you have solar + battery + EV, a smart charger is almost mandatory. The price difference is typically $400–$800 over a dumb charger - and the savings from solar-only EV charging cover that in under a year.
Vehicle-to-grid (V2G) and vehicle-to-home (V2H)
V2G lets your EV's battery act as a home battery - discharging back into the home (V2H) or grid (V2G) when needed. It's the holy grail: a 70 kWh EV battery is 5x bigger than a typical home battery, and could power your home for a week.
The catch in 2026: only a handful of EVs support V2G in Australia (Nissan Leaf, Mitsubishi Outlander PHEV, some BYD models). Most Teslas and modern EVs don't yet. Synergy and Horizon are still working out the network rules for V2G export. For now, treat V2G as a 2027–2028 feature, not something to plan around today.
The case for installing the battery now even if your EV is "later"
If you're planning an EV within 3 years but it's not in the driveway yet, install the home battery now anyway:
- The rebate stack is at peak value in 2026 - installing later loses federal rebate value.
- A 13.5 kWh battery covers a non-EV household well and absorbs an EV later.
- Modular systems (Sungrow SBR, BYD HVS) let you add capacity later when the EV arrives.
The case for waiting if you're EV-uncertain
If you're not sure whether you'll get an EV ever, size your battery for your current household - don't oversize "just in case." A 10 kWh battery is right for most non-EV WA homes. Adding capacity later is cheaper than overspending now.
Putting it together
For most EV-plus-battery WA households, the optimal setup looks like this: 8–10 kW of solar, 13.5 kWh battery, smart EV charger (Fronius Wattpilot or similar), Synergy Smart Home Plan tariff. Total install cost ~$25,000 list, down to ~$13,000 after rebates and trade-ins. Annual savings $2,500–$3,500. Payback under 5 years.
The calculator doesn't yet model the EV explicitly - but a 16–20 kWh battery setting captures most of the EV scenario for a planning estimate.