Sizing Your Solar System for a Future Electric Vehicle

The average Australian household solar system is usually sized around one thing: the way the home uses energy today.

That calculation changes the moment an electric vehicle (EV) enters the picture.

An EV is not just another appliance plugged into the house. Depending on how far you drive and when you charge, it can become one of the largest energy loads on the property. For some households, charging a vehicle every day can add as much demand as the rest of the home combined.

That is why it makes sense to think about future EV ownership before installing solar rather than trying to expand the system later. Oversizing a system unnecessarily can be just as costly as installing one that is too small, which is why understanding your likely future energy demand matters.

Let us look at what that means in practice.

How Much Power Does Charging an Electric Car Actually Use?

The exact figures vary between vehicles, battery sizes, and driving habits, but most EVs on Australian roads use between 15 and 20 kWh to travel 100 kilometres.

For a household driving around 50 to 60 kilometres each day, that typically translates to an additional 10 to 15 kWh of electricity daily.

To put that into perspective, many Australian homes consume between 16 and 20 kWh per day before an EV is added. Once a vehicle enters the mix, overall household consumption can increase dramatically.

This is where many homeowners get caught out.

A solar system that comfortably covers household consumption today may struggle once EV charging becomes part of the equation, particularly during winter when solar production naturally drops.

The goal isn’t necessarily installing the biggest system possible. It’s understanding the total demand of the household and designing a system around how that energy will actually be used.

Why Timing Matters More Than Total Generation

When people first look at solar and EV charging, they often focus entirely on how much electricity the panels produce.

Timing is often the bigger consideration.

Solar generation peaks during the middle of the day. Most people plug in their vehicle after work, precisely when solar production has already tapered off. That mismatch is one of the biggest challenges when pairing rooftop solar with EV charging.

One solution is to shift charging into daylight hours whenever possible. Smart charging technology allows homeowners to schedule charging around peak solar production rather than relying entirely on grid electricity overnight.

Our EV charger installation service includes smart charging systems that can detect surplus solar generation and automatically direct it toward the vehicle. Instead of exporting excess electricity back to the grid, you’re using it directly where it delivers the greatest value.

The other option is a solar battery. By storing surplus solar energy generated during the day, households can charge vehicles later in the evening using their own stored energy.

How to Size a Solar System for EV Charging

A simple way to approach this is to add your estimated daily EV energy requirement to your current household consumption and size the system around the combined figure, with some buffer built in for seasonal variation.

For a household currently using 20 kWh per day and adding an EV that needs 12 kWh per day, the total daily requirement becomes approximately 32 kWh. In the Illawarra and South Coast regions, a well-oriented rooftop system typically generates around 4 kWh per kilowatt of installed capacity per day in average conditions. A system sized at 8 to 10 kW would therefore be a reasonable starting point for that combined load.

The specifics will vary based on:

• Roof orientation and shading
• How many days per week the vehicle is driven and recharged
• Whether you plan to charge primarily during the day or overnight
• Whether battery storage is part of the plan now or in the future

In practical terms, an 8–10kW system typically requires:

• Around 18–24 modern solar panels
• Sufficient usable roof space
• Consideration of roof orientation and shading

Understanding how AC versus DC charging works at home is also relevant to the conversation— our guide to home EV charging covers that in detail.

Can You Charge Two Electric Vehicles at Home?

Yes, but it requires more deliberate planning. Two EVs effectively double the charging load, and a system that works comfortably for one vehicle may fall short for two without upgrades to both the solar capacity and the home’s electrical infrastructure.

Smart charging management becomes particularly important in this scenario—staggering charge times, prioritising the vehicle that needs the most charge, and integrating with solar production to avoid drawing heavily from the grid at peak tariff times.

Planning for Future Expansion

One common mistake is sizing a solar system around today’s electricity usage without considering future additions. An EV charger, home battery, second electric vehicle, or other major appliances can significantly increase demand over time.

Choosing a future-ready system can help avoid costly upgrades later. Solutions like Sigenergy batteries are designed to integrate battery storage, EV charging, and energy management within a single platform as your needs evolve.

Planning ahead can reduce future installation costs, minimise electrical rework, and make expansion much simpler down the track.

What About Solar Rebates?

If you’re increasing your system size to accommodate future EV charging, it’s worth understanding what incentives may be available before making a decision.

NSW residents may be eligible for federal Small-scale Technology Certificates (STCs), which help reduce the upfront cost of solar installation. Information about current solar incentives is available through both the Clean Energy Regulator and the NSW Government programs.

The solar rebate landscape continues to evolve, so it’s worth checking eligibility before finalising system design.

Let Us Guide You

At Solar X Energy, we regularly work with households across the Illawarra and South Coast who are planning for future EV ownership. Sometimes, that means installing a larger system from day one. Other times, it means designing a solar solution that can be expanded later as needs change.

Every home is different. The right answer comes down to driving habits, roof space, charging preferences, and long-term plans. 

Contact us today to learn more about sizing your solar system.