Turning midday production into range instead of a small feed-in credit — and what load balancing has to do with it.
The simple version
If you have rooftop solar, the cheapest km you will ever drive is often surplus kilowatt-hours into the car instead of into the grid for a tiny feed-in credit.
You do not need a perfect setup on day one. Even scheduled daytime charging on a sunny afternoon beats export tariffs in most of Australia. Fine-tuning with sensors comes later if you want it.
The economics that make this worth doing
Feed-in tariffs across Australia have collapsed. Exporting a kilowatt-hour now earns a few cents in much of the country, while importing one costs many times that. In some states midday export is worth close to nothing at all.
Meanwhile a kilowatt-hour put into a car battery displaces petrol. The gap between what your exported solar earns and what that energy is worth in the car is the entire case for solar charging, and it is a wide gap.
A 6.6 kW system producing surplus for five or six hours a day is enough to cover a very ordinary commute without buying a single kilowatt-hour from the grid.
How the charger knows there is surplus
This works because of the same hardware that does dynamic load balancing. Current sensors clamp around the main supply at the switchboard and measure what the whole property is importing or exporting in real time.
With that reading, the charger can be told: only draw what is currently being exported. Cloud passes over, production drops, the charger ramps down. Sun returns, it ramps back up. The kettle goes on, it gives way to the kettle.
Without those sensors a charger is blind and can only follow a fixed schedule — which is a crude approximation of solar charging and will happily import from the grid at full rate on an overcast day.
The three modes worth knowing
Solar only. The charger draws nothing but surplus. Cheapest possible kilometres, but on a poor day the car may gain very little. Right for a second car or a household with slack in its schedule.
Solar priority, grid top-up. Surplus first, then a defined minimum from the grid so the car reaches a target state of charge regardless of weather. This is the sensible default for most households.
Scheduled off-peak. Ignore solar and charge on the cheapest tariff window overnight. Best where a time-of-use or EV-specific tariff undercuts what your solar is worth, or in winter where production is thin.
There is no universally correct choice. It depends on your tariff, your production, and whether the car has to be full by morning.
The minimum-current problem
EV charging cannot be dialled down indefinitely. Under IEC 61851, the minimum current a charger may offer is 6 A — roughly 1.4 kW on single phase.
So if your surplus is only 800 W, there is nothing useful the charger can do with it. It either waits for more or takes a little from the grid. Some vehicles also dislike being throttled up and down repeatedly and will drop the session entirely.
Practically: solar charging works well on a system with real surplus headroom and becomes fiddly on a small or heavily self-consumed system. Worth knowing before you expect miracles.
Where AS/NZS 4777.2 comes in
AS/NZS 4777.2 governs how grid-connected inverter energy systems behave — export limits, voltage response, and how the system reacts when the grid moves outside its normal range.
It matters for solar charging because your inverter's export limit and its response behaviour shape how much surplus is actually available to the charger, and when.
If you already have PV, mention it when you ask us to specify a charger, and make sure your electrician knows both systems exist. Load balancing, an export limit and a battery in the same switchboard need to be commissioned as one system, not three.
If you also have a home battery
Now there is competition for the same surplus, and the priority order is a real decision: car first, battery first, or split.
A rough rule — if the car drives daily and the battery mostly covers the evening peak, prioritise the car during the day and let the battery take what is left. If the household's evening load is heavy and the car sits most days, invert it.
Either way the charger, the inverter and the battery need to be seeing the same measurement point. Commissioned together, this works well. Commissioned separately by three different trades, it usually does not.
Key takeaways
- With feed-in tariffs low, surplus solar is worth far more in your car than exported
- Real solar charging needs current sensors at the switchboard — schedules alone are a poor substitute
- Solar-only, solar-priority with grid top-up, and scheduled off-peak each suit different households
- The 6 A minimum charge current means small surpluses cannot be used
- Tell us and your electrician about existing PV or a battery so the site is commissioned as one system