When to charge an EV on a half-hourly tariff
In short: Charge your EV during the cheapest consecutive half-hourly periods that cover the energy you need before departure. Overnight is often cheaper, but daytime prices can fall when solar output is high. Compare the whole charging window using published rates, rather than a forecast or a single cheap half hour, and respect your charger’s limits.
Choose a complete charging window
Work out the energy you need before departure and the time your charger needs to deliver it. For example, 28 kWh takes about four hours at 7 kW before charging losses. Compare the average price across consecutive half hours covering the full charge, rather than choosing the lowest single rate. Allow extra time for losses and any charging slowdown.
Overnight or daytime solar?
Overnight demand is often lower, but sunny or windy days can bring cheaper daytime rates. If you have rooftop solar, compare the cost of grid charging with the export payment you give up by using your own generation. The best window depends on your tariff and when the car is at home.
Wait for published rates
Forecasts help you look ahead, but they are not confirmed prices. Once your supplier publishes rates for your region, compare the windows that finish before departure. Set the schedule in your car or charger and check that competing schedules do not override it.
Keep household loads within safe limits
Follow your car and charger manufacturers’ instructions. Use a properly installed charging point with suitable load management and avoid overloading the household supply when other high-power appliances run. Ask a qualified installer about your home’s capacity; do not improvise with extension leads. Read Electrical Safety First’s EV charging advice.
Is overnight always the cheapest time to charge an EV?
No. Overnight is often cheaper, but a sunny or windy day can offer cheaper daytime periods. Compare your region’s published rates for the full charge before setting a schedule.
Plan with the day’s rates on your iPhone
Octomiser shows the current half-hourly rate and the rates still to come, finds the cheapest window for the time you need and keeps live rates in Home and Lock Screen widgets. Today it works with Octopus Energy accounts in the UK, including the Agile tariff.
Download on the App Store