An EV can materially increase annual electricity use. The amount of extra solar that may be useful depends on how far the vehicle travels, its efficiency, when it is normally charged and whether charging can happen while solar is producing.
What matters most
Plan solar and battery sizing around the vehicle’s expected charging pattern, not only past electricity bills. How far it travels, when it is home and whether it can charge while solar is producing all shape the design.
- Include expected vehicle charging use before comparing solar and battery sizes.
- Check whether the vehicle is normally available to charge during solar-producing hours.
- Compare direct daytime charging, more solar and storage without assuming one option is always best.
Common questions
Why are past electricity bills not enough when an EV is planned?
Past bills do not show future vehicle charging. A reasonable estimate of expected charging use should be added before system sizes are compared.
Does an electric vehicle automatically mean a larger home battery?
No. The right approach also depends on available solar surplus, likely charging times and whether the vehicle can charge directly from solar.
Can daytime EV charging change the solar design?
Yes. Charging while solar is producing can use solar directly, so the vehicle’s normal location and charging window should be considered.
Charging time changes the answer
Daytime charging can use solar directly. Evening or overnight charging may rely more on the grid, or may make storage worth investigating if there is enough daytime surplus to charge the battery first.
Do not size only from old bills
If the EV is new or still planned, historical bills will not show the future charging load. I add a reasonable estimate of future EV consumption before comparing system sizes.
Home and business charging can be different
A home EV may spend the day away from the property and charge at night. A commercial fleet may return at different times, or vehicles may be onsite during daylight hours. The charging pattern matters as much as the annual kilometres.
EVs can change the battery decision too
An EV can increase later electricity use, but that does not automatically mean a stationary battery should be larger. I still check how much solar surplus is available, what the grid tariff is, and whether direct daytime charging provides a better result.
Example
A homeowner with a small existing solar system buys an EV and plans to charge mainly overnight. Before adding a large battery, I would compare more solar, charging-time changes and battery options rather than assuming storage is the only solution.
What I ask
- Which EV is owned or planned?
- Approximate kilometres driven each week
- When the vehicle is usually at the property
- When charging is likely to happen
- Existing charger or planned charger
- Whether more EVs may be added
- Existing solar and battery setup
The system should be designed around where the customer's energy use is heading, not only where it has been.
Planning for an EV?
Include the future charging load in a free full energy assessment, or start with the full calculator.