With an electric car, when you charge matters far more than how you charge. The electricity itself is the same; what changes is the price per unit at different times of day. Get the timing right and your motoring costs a couple of pence a mile, cheaper than anything burning petrol. Get it wrong and you pay several times over for the very same miles.
The cheapest time is the overnight off-peak window
On a time-of-use or dedicated EV tariff, electricity in the small hours costs a fraction of the daytime rate, because demand on the grid is low and suppliers want to soak up cheap overnight generation. Charging in that window, rather than during the day, is the single biggest saving you can make on running an electric car. As the cost of charging at home guide shows, the same car can cost about 2p a mile charged off-peak against around 7p a mile on a standard daytime rate, with no change to the car at all. The whole game is making sure your charging happens in that cheap window.
You need the right tariff first
None of this works on a flat single-rate tariff, where electricity costs the same at three in the morning as at six in the evening. To get cheap overnight charging you need a smart meter and a time-of-use or EV tariff that has a defined off-peak window. These typically offer a set block of cheap hours overnight, often something like five hours in the small hours, though the length of the window and the gap between the cheap and peak rates vary between tariffs. It pays to compare them on those two points, because a wider window and a deeper discount are what make the saving large.
Avoid the peak
The flip side of the cheap window is an expensive one. Many time-of-use tariffs charge a premium during the early-evening peak, roughly the late afternoon to mid evening when the whole country gets home and switches things on. Charging then is the worst case, paying the top rate for energy you could have bought for a fraction overnight. If your car plugs in when you get home and starts charging immediately, it is drinking at the most expensive time of day. The answer is not to babysit the plug, but to schedule the charge so it waits for the cheap hours.
How to charge automatically in the cheap window
You should never have to set an alarm for the small hours. There are three ways to make charging happen off-peak on its own. Most electric cars let you set a charging schedule in the car itself, so it will not draw power until the time you specify even if it is plugged in earlier. Most dedicated home wall chargers can do the same, holding off until a set window. And some smart EV tariffs go further, taking control of the charging themselves to fill the car during the cheapest hours, sometimes spreading it across the night to catch the very lowest prices. Any of these turns plugging in when you get home into a charge that quietly happens at the cheap rate while you sleep.
If you have solar, daytime can be cheaper still
There is one exception to the overnight rule. If you have solar panels, the cheapest electricity you will ever have is the surplus your own roof generates on a sunny day, which would otherwise be exported for a low rate. Charging the car from that midday surplus costs you nothing beyond what you have already spent on the panels. Some chargers can be set to draw only from solar surplus, topping up the car whenever the panels are producing more than the house is using. For a solar household the best time to charge can be the middle of a sunny day rather than the dead of night, and the solar battery guide covers the related question of storing that surplus.
Timing that is kinder to the battery
The cheap overnight window happens to line up with what is best for the battery's long-term health, which is a happy coincidence. Slow AC charging at home is gentler on the cells than repeated rapid charging, and for daily use it is better not to sit the battery at a full 100 per cent or run it to empty. A common approach is to set the charge limit to around 80 per cent for everyday driving and only fill to 100 per cent before a long trip. Scheduling the charge to finish shortly before you leave in the morning, rather than hitting full at midnight and sitting there for hours, is gentler still. Off-peak overnight charging gives you all of this for free as a side effect of chasing the cheap rate.
Cold mornings: precondition while plugged in
In winter, warming the car's cabin and battery while it is still plugged in, rather than after you set off, draws that energy from the cheap mains supply instead of from the battery on the road. Most electric cars let you schedule preconditioning to finish around your departure time. Done while still on the charger in the off-peak window, it costs little and means you set off with a warm cabin and a battery already at temperature, which also improves your range for the journey. The EV charging in winter guide covers the cold-weather range loss and how to limit it in full.
The bottom line
The best time to charge an electric car is overnight, in the off-peak window of a time-of-use or EV tariff, set to run automatically so you never think about it. If you have solar, a sunny midday is better still. Avoid charging during the early-evening peak, schedule rather than babysit, and let the cheap hours do the work. Combined with the figures in the cost of home charging guide, this is what turns an electric car into the cheapest thing on the road to fuel.