How to Size Your Solar System for EV Charging

You have got solar on the roof. You have got an EV in the garage, or you are about to. The next question is inevitable: is my solar system big enough to charge the car, or do I need to upsize?

The short answer for most households is that you need 2–3 kW of extra panels beyond what your home already uses. But the real answer depends on how far you drive, when the car is home, and whether you have a battery to bridge the gap between solar hours and charging hours.

This guide walks through the sizing maths step by step, gives you a recommendation table you can take to your installer, and explains the charger types, smart charging options, and export limit quirks that affect the decision. If you want the broader picture on charging your EV with solar, start there and come back here for the sizing detail. And if you are still deciding whether solar makes financial sense at all, our is solar worth it analysis covers the payback maths.

Before you can size the solar, you need to know the load. Most modern EVs sold in Australia (the Tesla Model 3, BYD Atto 3, Hyundai Ioniq 5, MG ZS EV) consume roughly 15–20 kWh per 100 km of driving. Smaller, more efficient models sit at the lower end; larger SUV-style EVs sit at the upper end.

According to ABS data, the average Australian drives about 38–40 km per day (roughly 14,000 km per year). At an average efficiency of 17.5 kWh/100 km, that translates to about 7–8 kWh of daily charging demand.

That is equivalent to running a split-system air conditioner for 4–5 hours. It is a meaningful load, but not an enormous one, and importantly, it is a predictable one. You know roughly how far you drive each day, which makes solar sizing straightforward.

Once you know how many kWh your car needs each day, converting that to solar panel capacity is simple division.

Australia gets roughly 4–5.5 peak sun hours per day depending on location. Sydney averages about 4.7, Brisbane about 5.2, Melbourne about 4.0, and Perth about 5.5. These are the “equivalent hours of full sunshine” that determine how much energy each kW of panels produces daily.

The formula is straightforward:

Here is a practical recommendation table that covers the most common Australian household scenarios. These assume typical household consumption of 16–20 kWh per day and include the EV charging load on top.

The type of EV charger you use dramatically affects how well you can utilise solar. There are two main categories for home charging.

The right system size gets the energy onto your roof. A smart charger makes sure it ends up in your car instead of being exported at 5 cents per kWh. Solar-aware chargers use CT clamps on your switchboard to monitor excess production in real time and adjust the charging rate to match.

This is the single biggest factor in whether your solar system “pays for” your EV or not. We covered it in depth in our daytime vs off-peak charging analysis, but the summary is simple.

Every kWh you charge from your own solar during the day is worth the difference between your grid import rate (25–35c/kWh) and your feed-in tariff (3–8c/kWh). That is a 20–30 cent advantage per kWh. Over a year of typical driving (~2,700 kWh), solar charging saves $540–$810 compared to off-peak night rates, and $800–$1,200 compared to peak grid rates.

The practical challenge is obvious: many people's cars are at work during peak solar hours. That is where batteries and weekend charging come in. More on that below.

If your car is at work during solar hours, a home battery bridges the gap. The concept is elegant: your battery charges from excess solar during the day while the car is away. When you get home in the evening, the battery feeds stored solar into your EV charger. You are still effectively driving on sunshine, just time-shifted.

There is roughly 10–15% round-trip efficiency loss through the battery charge/discharge cycle, so you need slightly more solar to compensate. But the maths still work out dramatically better than buying grid power at 30+ cents per kWh.

The battery also does double duty: it powers your house during the evening peak, displacing the most expensive grid electricity of the day. One investment solving two problems.

Here is something most sizing guides miss. Many distribution network service providers (DNSPs) limit how much solar you can export to the grid, commonly 5 kW in states like SA and parts of QLD. Some new connections are being approved with zero export limits.

This matters for EV charging because it changes the economics of a larger system. Without an EV, a 13 kW system in a 5 kW export-limited area wastes any production above what the house uses plus 5 kW of export. The inverter simply throttles back and curtails the excess.

But with an EV charger, that curtailed power goes into the car instead of being wasted. An EV effectively removes the export limit as a constraint, because the car absorbs the surplus on-site. This means a larger solar system makes even more sense when you have an EV. You can install 10–13 kW without worrying about hitting the export cap, because the car soaks up the excess.

Whether you are adding an EV to an existing solar system or designing from scratch, here is the decision framework.