How Much Solar Does an Electric Vehicle Need? EV Charging with Rooftop Solar Explained

You don't need a separate solar system just for an EV. The right solar size depends on how far you drive, your EV's efficiency, when you charge, and how much electricity your home already uses.

In Melbourne, Australian Government guidance puts average solar generation at about 3.6 kWh per day for every 1 kW of installed solar capacity, averaged across the year.

So, purely on annual-average energy:

could theoretically generate enough energy to cover that EV's average daily driving energy.

For most homeowners, the better question is: How large should my total solar system be to cover my home + EV, while making the best use of the electricity I generate?

The easiest way to estimate your EV's solar requirement is to start with kilometres driven, not the EV battery's total capacity.

The basic formula

For example, if your vehicle uses 18 kWh/100km:

These are illustrative calculations using 18 kWh/100km, not universal EV consumption figures.

Your actual vehicle may consume more or less depending on:

And the electricity drawn from the wall can be higher than the energy actually stored in the vehicle because charging has losses.

The Australian Government says the average output of 1kW of rooftop solar in Melbourne is about 3.6kWh per day when averaged across the year. Actual generation is higher in summer and lower in winter. That gives us a useful planning calculation.

Assuming:

• EV consumption = 18 kWh/100km
• Melbourne solar = 3.6 kWh/kW/day
• No allowance yet for household electricity
• No allowance yet for charging losses

Imagine your home already uses 15 kWh/day and your EV adds 7.2 kWh/day. Your combined electricity requirement becomes approximately 22.2 kWh/day.

Using the Melbourne long-term average of approximately 3.6kWh/day per installed kW:

That gives a rough annual-energy starting point of around 6.2kW of solar. And this is before considering:

This is why solar sizing should be based on the whole home, not just the car. Solar Victoria specifically recommends reviewing actual household energy use and considering future electricity demand from appliances and an electric car when deciding on solar system size.

Using the same 18 kWh/100km EV consumption and Melbourne's 3.6 kWh/kW/day long-term average solar output:

This is often more important than the theoretical solar capacity. Imagine you have a 6.6kW solar system. Your solar might produce plenty of electricity between late morning and afternoon.

But if you:

• Leave home at 7:30am
• Drive to work
• Return at 6:00pm

your EV isn't available to absorb most of that daytime solar. You may therefore export solar during the day and charge the EV in the evening. Alternatively, you could use:

if the battery and charging system are designed for that operation. This can be useful, but it is not automatically the most economical approach.

This is the ideal scenario. For example:

This is called load shifting or self-consumption — moving electricity demand into the hours when your solar is generating.

This is another useful way to think about the problem. Suppose your EV consumes 18 kWh per 100km and your solar system produces a surplus of 9 kWh that you can actually direct into the vehicle.

The theoretical driving range represented by that energy is:

So approximately 9kWh of usable charging energy represents around 50km of driving for that example vehicle. This is often more useful than asking: "Can solar fully charge my EV?"

This is one of the biggest misconceptions about solar EV charging. Suppose your EV has a 60kWh battery. You might think: "I need 60kWh of solar every time I charge."

Not necessarily. If you drove 35km yesterday, your energy requirement could be only around:

So a smart solar charger could potentially replenish approximately the energy used for that day's driving without filling the entire battery.

A 6.6kW system is common in Australian homes, but whether it is sufficient depends on what else the home consumes. Using the Australian Government's Melbourne average of approximately 3.6kWh per kW per day:

as a long-term average generation estimate. That is generation, not guaranteed usable EV charging energy. The home may consume electricity for:

Whatever the home consumes directly is not available to the EV. The EV then competes with other daytime loads for solar electricity.

Using the same Melbourne long-term average:

Again, this is a broad annual-average generation figure. A 10kW system can provide significantly more energy for a home with:

This is where simplistic solar calculations can fail. Melbourne solar does not produce the same amount of electricity every day. Solar Victoria notes that a Victorian solar system can generate more than twice as much electricity in December as in July.

So a system that appears to generate enough energy on an annual-average calculation may produce much less on a cloudy winter day. That doesn't make solar unsuitable for EV charging. It means you should expect a combination of:

rather than assuming the EV will always be charged entirely from rooftop solar.

Sometimes. A battery can store excess solar during the day and provide electricity later. Solar Victoria explains that a household battery can store excess solar energy for use later when solar generation falls. For example:

This can increase the amount of solar energy ultimately used by the household. But there is an important consideration. If your battery is small and your EV has a large battery, trying to charge the EV entirely from the home battery may require a very large amount of stored energy.

Solar Victoria says most EV owners charge at home using a standard electrical outlet, while faster charging can be provided through dedicated home charging equipment.

A standard outlet can be adequate for some drivers who only need a small daily top-up. A dedicated Level 2 charger can make more sense when you:

Not automatically. The appropriate charger depends on:

Solar Victoria notes that Level 2 chargers can be installed by an electrician where the home has a three-phase connection, but homeowners should obtain advice about what charging level their property can support.

You may not need more panels immediately. Start by looking at your current system. Check:

This is where planning becomes much more valuable. Don't size solar based only on:

Instead consider:

For example:

The numbers above are illustrative, but the principle is important. Solar Victoria specifically advises considering whether electricity consumption will increase after purchasing an EV or other electric appliances.

This is where solar + EV planning gets particularly interesting. A home might have:

This creates several flexible loads that can absorb solar generation. Instead of:

you may achieve more:

depending on the home's real-time demand and system controls. This is one reason Samsun Energy's broader approach of considering solar, battery, heat pump and EV requirements together can be more useful than purchasing each technology independently.

Consider a hypothetical household:

So approximately 6.2kW of solar capacity would generate the same annual-average amount of electricity as this illustrative combined daily consumption.

But that does not mean a 6.2kW system will make the household energy-independent. Why? Because:

• Solar generation varies by season
• The EV may be away during the day
• Household demand isn't constant
• Charging has losses
• Shading and orientation affect output
• Network export limits may apply
• Some electricity will be imported at other times

This is why system design needs actual household data rather than a single formula.

Instead of asking: "How many solar panels does my EV need?" ask these five questions:

Solar orientation can affect when your electricity is generated. A north-facing system generally maximises annual solar production in Victoria. But an east/west design can shift more generation toward morning and afternoon. For an EV owner, that timing can sometimes be valuable.

If your EV returns home around 3–4pm, west-facing generation may align better with your charging window than a system producing most of its energy around midday. That doesn't mean west is automatically better. Roof shape, shading, annual generation, household demand and network constraints all matter.

Adding an EV does not simply mean adding more panels. The solar system also needs an appropriate inverter and electrical design. Australian Government guidance notes that grid-connected solar systems can be subject to network limits on inverter capacity and electricity exports.

So before expanding an existing solar system, check:

Often, more solar can be useful when the household is adding an EV, because the EV creates another significant electricity load. But the economics depend on what happens to the additional generation. If additional solar is mostly exported at a low feed-in tariff, its value may be different from solar that directly charges your EV.

At Samsun Energy, the useful starting point isn't: "Which EV charger do you want?" It is:

A calculator can tell you that an EV needs, for example, 7.2kWh/day. It cannot automatically tell you that your solar panels will provide all 7.2kWh directly to the car. That's because energy and timing are different problems.

You could have:

but only:

if the rest is being used by the home or exported. Conversely, you might have enough annual solar generation to cover your EV's annual electricity requirement but still need grid electricity during winter evenings.

There isn't one universal solar size for an EV. For an illustrative EV consuming 18kWh/100km:

In Melbourne, 1kW of solar produces around 3.6kWh/day on a long-term average, although actual output varies substantially by season, weather, orientation and shading.

So an EV travelling 40km per day might theoretically require around 2kW of solar generation capacity to produce an equivalent amount of energy on an annual-average basis.

For many households, the most effective combination is:

• Australian Government — Solar panel generation and sizing
• Australian Government — How to size your solar system
• YourHome — Rooftop solar
• Solar Victoria — Getting your home EV-ready
• Solar Victoria — Planning your solar electricity system
• Solar Victoria — Solar assessment calculator
• Solar Victoria — Zero-emissions vehicle facts
• Solar Victoria — How a solar battery system works