An EV adds a significant, predictable load to your home. This guide explains how much extra electricity an EV uses, whether your existing solar system is still the right size, how to charge most efficiently, and whether a battery makes sense alongside an EV.
Key findings
- An EV driven 15,000 km/year adds roughly 8 to 12 kWh of daily charging demand. For most households this means existing solar is undersized.
- The most efficient way to charge an EV is directly from solar during the day using a smart EV charger, not via a home battery.
- A 6.6kW system is usually not enough for an EV household. Most benefit from upgrading to 8kW or larger.
- Charging from the grid at around 30 cents per kWh costs roughly $600 to $800 a year for typical Australian driving. Charging from surplus solar costs close to nothing.
- An EV is a large battery on wheels, with a smart charger it absorbs surplus solar that would otherwise be exported for very little.
How much electricity does an EV use?
Most EVs use 14 to 18 kWh per 100 km. At 15,000 km/year that's around 2,100 to 2,700 kWh/year, $630 to $810 at 30¢/kWh from the grid. The same kilometres charged from your own solar costs close to zero.
Is your existing system still the right size?
If you had solar installed before the EV, almost certainly not. A household using 20 kWh/day before the EV, adding 10 kWh of daily charging, now needs a system sized for 30 kWh. A 6.6kW system generating 24 to 28 kWh/day is no longer sufficient, particularly in winter.
How to check
- Find your pre-EV daily consumption from old bills.
- Estimate EV daily charging: annual km ÷ 365 × (kWh per 100km ÷ 100). Most EVs land at 8 to 12 kWh/day.
- Compare combined demand against your inverter app's daily generation. If demand consistently exceeds generation, you're drawing heavily from the grid, that's the case for upsizing.
The smartest way to charge with solar
Daytime solar charging
A smart EV charger reads your solar surplus in real time and adjusts charging rate to match. The EV soaks up what would otherwise be exported for 3 to 10¢/kWh. Effective cost: close to zero per kilometre.
Evening grid charging
Charging at night from the grid costs around $600 to $800/year for typical Australian driving. On a time-of-use tariff with cheap overnight rates, $300 to $500. Still significantly more than daytime solar charging.
What to tell your installer
- Your annual kilometres and EV model, this determines daily charging demand.
- When you typically charge, daytime from solar is most efficient.
- Whether you plan a second EV, designing for it now avoids another upgrade later.
Sources
- Australian Government, Energy Rating: electric vehicles, energyrating.gov.au · energyrating.gov.au