Charging an EV with solar panels and smart tariffs

How solar-matching charger modes work

Many smart EV chargers offer a solar-matching or solar-diversion mode, which monitors how much surplus electricity your solar panels are generating beyond what the home is currently using, and adjusts the charging rate to use that surplus rather than drawing from the grid.

In practice, this often means slower, variable-speed charging during the day that ramps up and down as cloud cover or household demand changes, rather than a constant, fixed charging rate. Some chargers offer an eco mode that blends a small amount of grid import with solar surplus, and a fully solar-only mode that pauses charging if solar surplus drops too low.

Not every home charger model supports solar matching, and it typically needs the charger to be able to communicate with your solar inverter or an export sensor, so check this compatibility specifically if solar charging matters to you.

Smart EV tariffs explained

Separately from solar, some energy suppliers offer tariffs specifically designed around electric vehicle charging, typically with a significantly cheaper rate during a set overnight window, intended to encourage charging when overall electricity demand on the grid is lower.

These tariffs often work alongside the charger's own scheduling feature, so you set the car to charge within the cheap window rather than as soon as it is plugged in, and the smart charger or vehicle handles the timing automatically.

Combining solar and a smart tariff

For households with solar panels, a common approach is to prioritise solar-matched charging during sunnier months and daytime hours, when it is being used, and top up any additional charge needed overnight using a cheap smart tariff rate, especially in winter when solar generation is lower.

For illustration only, assume a household typically needs 8kWh of charging on a given day. On a day when solar surplus covers 3kWh of that during daylight hours, and the remaining 5kWh is charged overnight at an assumed smart tariff rate of 15p per kWh rather than a standard rate of 30p per kWh, the saving on the overnight portion alone would be 5 × (£0.30 − £0.15) = £0.75 for that day, before accounting for the solar portion which costs nothing additional to generate.

Figures in this example are illustrative assumptions only, used to explain the principle of combining solar and smart tariffs. They are not current tariff rates. Check your own solar generation data and tariff terms for a realistic comparison.

Practical considerations

Solar-matched charging tends to work best when the car is at home and plugged in during daylight hours, which may not suit everyone's daily routine, particularly those who commute and are away from home during the day.

Smart tariffs usually require a compatible smart meter and sometimes a specific type of charger or app to schedule charging automatically within the cheap window. Check compatibility with your supplier before switching tariffs.

Some smart tariffs have specific terms about the time windows, which can change seasonally or be adjusted by the supplier, so it is worth checking the current terms regularly rather than assuming they stay fixed.