The two options
Daytime solar charging. Plug in while your panels are generating, so the car draws directly from solar rather than the grid. The cost to you is not zero: it is the feed-in tariff you give up by not exporting that electricity instead, typically 3 to 12 cents per kWh depending on your state and retailer.
Overnight off-peak or EV tariff charging. Plug in overnight on a controlled-load, off-peak, or dedicated EV tariff. Rates vary widely by network and retailer, but a genuinely cheap overnight rate can sit in a similar range to a typical feed-in tariff, sometimes lower, sometimes higher.
Working through the numbers
For a full home charge of a typical EV battery (around 60 kWh, roughly 300 to 400km of range):
| Charging method | Effective rate | Approx. cost per full charge |
|---|---|---|
| Daytime solar (opportunity cost of feed-in) | 3 to 12 c/kWh | $1.80 to $7.20 |
| Genuine overnight/EV off-peak tariff | 8 to 20 c/kWh | $4.80 to $12.00 |
| Standard flat or peak usage rate | 30 to 45 c/kWh | $18.00 to $27.00 |
Ranges are indicative and depend heavily on your specific retailer, network tariff, and state. Check your own plan's feed-in tariff and any overnight or EV-specific rate before assuming either figure.
Our take on charging day vs night
Daytime solar charging usually wins on pure cost, because you are comparing against a low feed-in tariff rather than a retail usage rate. The catch is practicality: most households are not home during the day to plug in, and few EV chargers are set up with the smart scheduling or solar-diversion hardware needed to automatically follow solar output.
If you are genuinely home during the day (or work from home), prioritise a smart charger or an EV plan with solar-diversion charging and charge on sunny days. If your household is out during work hours, a well-chosen overnight or dedicated EV tariff is the realistic option, and the gap between it and daytime solar charging is often smaller than people expect, particularly against a mid-range feed-in tariff.
Either way, compare the total plan (usage rate, feed-in tariff, and any overnight/EV rate together) rather than optimising for one number in isolation. A high feed-in tariff plan with an expensive standard usage rate can cost more overall than a moderate feed-in plan with a genuinely cheap overnight rate.
Compare solar and EV-friendly plans
Find a plan with the right combination of feed-in tariff and overnight rate for how you actually charge.
Compare plans at your addressDoes a battery change the answer?
A home battery is most useful if you need to charge in the evening after arriving home from work, since it lets you store cheap daytime solar and use it after sunset instead of paying a peak or standard grid rate. It does not change the daytime-vs-overnight comparison itself, since a battery-stored kWh has the same opportunity cost as one used directly during the day. Where a battery earns its keep is avoiding the most expensive part of the day (the evening peak on a time-of-use tariff) for charging that cannot happen during daylight hours.
For more on the underlying feed-in tariff numbers behind this comparison, see our solar feed-in tariffs guide, and for time-of-use pricing windows by state see our smart meters guide.