Australia Solar EV Charging at Home: When the Math Works

Start with your annual driving distance. A typical Australian driver travels 15,000 km/year. At an EV efficiency of 6 km/kWh, that is 2,500 kWh/year of charging energy. With 10% charging losses, you need about 2,775 kWh/year from solar. In Sydney (4.5 peak sun hours), that requires roughly 2.2 kW of additional solar capacity — about 5-6 standard panels (400W each). In Brisbane (5.0 peak sun hours), the same EV needs only about 1.9 kW extra (4-5 panels). In Melbourne (4.0 sun hours), about 2.5 kW extra (6-7 panels). The numbers change if you drive more (or less) and if your EV is more (or less) efficient.

The biggest variable is when your car is home. If you work from home or the car sits in the driveway during the day, you can charge directly from solar with minimal grid interaction. This is the most cost-effective scenario because every kWh used directly avoids the retail rate (25-36c/kWh) and avoids exporting at low FiT rates (4-12c/kWh). If the car is away during the day, you will either import grid power (at high retail rates) or export solar (at low FiT rates) — a battery can help by storing midday solar for evening car charging, but adds significant cost. Compare the solar EV scenario with simply charging the car overnight on an off-peak tariff (as low as 8-15c/kWh in some areas).

In Australia, many retailers offer off-peak electricity rates as low as 8-15c/kWh during overnight hours (typically 10pm-6am). If you have a time-of-use tariff and charge your EV overnight, the cost can be as low as AU$300-400 per year for 15,000 km — compared to AU$3,000-4,000 for petrol. Adding solar panels to offset EV charging may still make sense if you also want to offset your household load, but the breakeven calculation changes. A dedicated "solar for EV" system without household load offset may have a longer payback than a combined whole-home + EV system.

The STC rebate (AU$2,500-3,000 on a 6.6kW system) reduces the upfront cost of solar by 35-45%, making solar-for-EV economics substantially better. However, FiT rates matter: if you export most of your solar production (because the car is away during the day), the FiT rate determines your return. A 5c FiT means exported solar is worth only AU$125/year for 2,500 kWh exported. Self-consuming that same 2,500 kWh saves AU$625-900/year at retail rates. This 5× difference is why daytime home charging (or battery storage) makes solar EV charging far more valuable than relying on FiT exports alone.

Key assumptions: EV energy need = annual km divided by vehicle km/kWh. Solar production should use location, tilt, orientation, shading, and system-loss assumptions. Battery need depends on whether the vehicle is home during solar production hours. Important caveats: Do not call solar charging zero-cost without acknowledging the upfront system cost. Separate solar-only EV offset from whole-home solar ROI. Consider that adding EV charging to an existing solar system may push you into a higher self-consumption bracket, improving your overall solar ROI without adding panels — this is often a better first step than increasing system size.