Top up from grid if needed

When to use it

Turn this on when you need the EV to reach the target every day — for example because you have a fixed long commute or a known trip the next morning. With the option on:

• On sunny days the simulator fills the EV from solar as usual. Grid import isn’t needed and isn’t triggered.
• On cloudy or short-day-of-year days when solar falls short, the simulator imports from the grid during off-peak hours (typically overnight) to close the gap. Imports stop the moment the daily target is reached.

Leave it off when you’re happy for the EV to be charged only when the sun shines — you accept that on bad-solar days the EV ends the day partially charged. This is the cheapest possible mode but requires flexibility in your driving schedule.

How “optimal time” is decided

The simulator imports only at steps where the buy price is below your tariff’s peak threshold and the step isn’t flagged as a peak window. In practice that means Australian time-of-use tariffs will see imports overnight (low rates) and avoid the late-afternoon / evening peak. Each off-peak step charges at the full charger rate until the daily target is met, then stops.

The off-peak rule is a simple “below peak” threshold — any step whose buy price is below the tariff’s peak band qualifies, with no further ranking inside that window. This works well for typical AU time-of-use tariffs where off-peak rates are flat across the eligible hours.

Cost vs reliability trade-off

Grid imports cost real money — around 20–30 c/kWh on AU off-peak rates — whereas solar charging is effectively free (or worth what you’d have earned by exporting it). The trade-off is whether the predictability of always meeting the target is worth that cost. Compare the simulator’s Net cost today with the option on vs off to see the daily price of guaranteed charge.