Why timing matters for EV charging - and how most people get it wrong
The average EV driver gets home somewhere between 5pm and 7pm. They park in the drive, plug in, and the car starts charging immediately. It feels like the right thing to do. The car is empty, the charger is right there, and the instinct is to fill it up.
That instinct costs hundreds of pounds a year.
On Octopus Agile, electricity between 4pm and 8pm typically costs 25p to 45p per kilowatt hour. On a cold winter evening, prices spike above 50p. This is the evening peak - when millions of people get home simultaneously, turn on their ovens, fire up their heating, and yes, plug in their electric cars. The grid is under maximum stress. Prices reflect that.
Wait until midnight. The same electricity - the same electrons flowing through the same cable into the same battery - costs 3p to 8p per kilowatt hour. Not 10% cheaper. Not half the price. Between five and fifteen times cheaper.
A 60kWh battery charged from empty at peak rates costs around £22.40. The same charge completed overnight on Agile costs £2.36 to £4.80. That difference - per charge, happening two or three times a week, for fifty-two weeks a year - is the £400 to £600 annual saving. It is real. It is consistent. And it requires exactly one setup step.
Tonight's cheapest charging window - how to find it
Octopus Agile prices for the next day are published every evening at around 4pm. They cover 48 half-hourly slots from midnight to midnight. The cheapest windows vary day to day based on wind generation, grid demand, and wholesale market conditions - but the overnight period from midnight to 6am is almost always significantly cheaper than evenings.
The practical approach is simple. Check tomorrow's prices on AgileAlert before you go to bed. The live dashboard shows every half-hourly slot for your region. Look for the cheapest consecutive hours overnight. Set your car's departure time so it charges through that window and finishes just before you need it.
On most nights, the cheapest window is somewhere between 1am and 5am. On windy nights, it can be earlier or later. On nights following plunge pricing events, prices can go negative - meaning the grid literally pays you to charge. The dashboard will show you exactly which hours those are.
You do not need to stay up to midnight to do any of this. You set the departure time once, check the approximate window, and let the car handle the rest. The whole process takes under two minutes once you know where to look.
The cost difference: peak vs overnight - the numbers that change everything
Let the numbers speak for themselves. A 60kWh battery - typical for a Nissan Leaf, VW ID.4, or base Tesla Model 3 - charged from 20% to 100% uses approximately 48kWh of electricity.
| Charging time | Typical Agile rate | Cost for 48kWh charge |
|---|---|---|
| 5pm to 8pm (peak) | 35 - 45p/kWh | £16.80 - £21.60 |
| Midnight to 6am (overnight) | 3 - 8p/kWh | £1.44 - £3.84 |
| Plunge pricing event | -20p to 0p/kWh | Free or earn money |
The saving per charge is roughly £15 to £18 in favour of overnight charging. Charge twice a week. That is £1,560 to £1,872 a year at the extreme, though realistic driving patterns and partial charges bring this down to the £400 to £600 figure Octopus Energy reports for drivers covering 10,000 miles annually.
Even on a conservative day when overnight prices are 10p instead of 3p, you still pay £4.80 versus £19.20 at peak. The overnight window wins every single night.
Setting departure time on your EV: Tesla, Nissan, VW, BMW, Kia, Hyundai
Every major EV sold in the UK supports scheduled charging. The specific steps vary by manufacturer. Here is exactly how to set departure time on the most common cars on British roads.
Tesla (Model 3, Model Y, Model S, Model X)
Open the Tesla app or use the car touchscreen. Go to Charging, then Schedule. Set a departure time - for example, 7:30am. Tesla calculates backwards and begins charging at the cheapest overnight window to ensure the battery is at your target level by departure. Enable off-peak charging in your Tesla account settings to let the car automatically seek cheaper rate periods. With Agile, the departure time method works best: set it to your morning leave time and let the car begin charging around 1am to 2am automatically.
Nissan Leaf and Nissan Ariya
Use the MyNissan app or the in-car charging schedule menu. Set a timer with a departure time or a direct start time. The Leaf supports two separate charging timers, which is useful for setting a weekday morning window and a weekend morning window independently. Go to Settings, then Charging, then Timer Settings. Enter your departure time and target charge level.
Volkswagen ID.3, ID.4, ID.5, ID.7
Use the MyVolkswagen app or the car's infotainment menu. Navigate to Charging Settings, then Timers. You can set up to three charging profiles with departure times, charge targets, and climate pre-conditioning. The pre-conditioning feature is particularly valuable on cold mornings: the car warms the cabin while still plugged in, using cheap overnight electricity instead of battery energy, so you lose no range to heating.
BMW iX, i4, i5, i7 and MINI Electric
Open the My BMW app. Go to Vehicle, then Charging Settings, then Charging Schedule. Set your preferred departure time and whether you want the car pre-conditioned. BMW also supports tariff information entry - you can manually enter Agile-style rate periods, though the manual entry is less useful than simply setting departure time and letting the car work backwards from your target.
Kia EV6, EV9, Niro EV
Use the Kia Connect app. Go to Charge Settings, then Scheduled Charging. Set a departure time and a target charge percentage. Kia supports off-peak scheduling with a start time and end time window - set the window as roughly midnight to 6am and the car will charge within that period to reach your target level.
Hyundai IONIQ 5, IONIQ 6, Kona Electric
Use the Hyundai Bluelink app. Navigate to Charge Settings, then Scheduled Charging. Set a departure time and the app calculates when to begin charging. The IONIQ 5 and 6 also support pre-conditioning, so you can arrive at a warm car on winter mornings without burning range.
Smart chargers: OHME and the Agile API connection
Setting departure time on your car is the manual approach. It works well. But there is a smarter option: a charger that reads Octopus Agile prices directly and charges automatically during the cheapest slots.
OHME is the standout product in this category. OHME home chargers have a direct integration with the Octopus Energy API. Connect your OHME to your Octopus account, set a departure time, and the charger handles the rest. It reads tomorrow's half-hourly Agile prices, calculates the cheapest windows that will deliver your required charge by your departure time, and switches on and off automatically through the night.
This means that on a night when prices are cheapest between 2:30am and 4:00am, OHME charges during those specific 30-minute slots rather than running a fixed overnight window. It extracts maximum savings without any manual intervention beyond the initial setup.
Other smart chargers with Agile compatibility include Andersen A2, Pod Point, and Zappi (via EDDI integration). The OHME integration is the deepest and most automated for Agile customers, but all of these charge on a schedule that eliminates peak-time charging.
The cost difference between a dumb charger (charging whenever you plug in) and a smart charger on Agile is, over three years of typical driving, equivalent to the cost of the smart charger itself. After that, it is pure saving.
Plunge pricing: charging for free (sometimes earning money)
Five to ten times every month, something remarkable happens on the UK grid. Wind turbines are spinning at full capacity. Demand is lower than forecast. The grid has more electricity than it can use. So it does the only thing available to it: it drops the wholesale price below zero.
On Octopus Agile, this translates to negative unit rates as low as -20p per kilowatt hour. When this happens, charging your EV does not cost money. It earns money. For every kilowatt hour that flows into your battery, Octopus credits your account.
A 60kWh charge during a plunge pricing event at -10p per unit generates a £6 credit. At -20p, that same charge generates a £12 credit. You are not just charging for free. You are being paid to store energy in your car battery during periods when the grid has surplus supply.
The challenge is that plunge pricing events are not always predictable far in advance. They show up clearly in the published price data at 4pm the day before, and AgileAlert will show them in the overnight price schedule. Check tonight's prices to see if tomorrow's overnight window includes any plunge pricing periods.
With a smart charger like OHME set to charge during the cheapest windows, you capture plunge pricing automatically. With manual departure time scheduling, you capture it if the plunge event falls within your charging window. Either way, it is genuinely free energy that most EV drivers currently pay 35p a unit for instead.
How much could you save? Annual saving table by mileage
The exact saving depends on your car's efficiency, your mix of home and public charging, and how consistently you shift to overnight charging. These figures assume a typical efficiency of 3.5-4 miles per kWh and home charging from the standard 3.7kW or 7kW home wallbox.
| Annual mileage | Approximate annual home charging cost at peak | Annual cost on overnight Agile | Annual saving |
|---|---|---|---|
| 5,000 miles | £350 - £450 | £50 - £100 | £150 - £225 |
| 10,000 miles | £700 - £900 | £100 - £200 | £300 - £450 |
| 15,000 miles | £1,050 - £1,350 | £150 - £300 | £450 - £675 |
| 20,000 miles | £1,400 - £1,800 | £200 - £400 | £600 - £900 |
These figures assume shifting all home charging from peak (5pm to 8pm) to overnight (midnight to 6am) on Octopus Agile. The saving range reflects variation in Agile overnight prices throughout the year - cheaper in spring and summer when wind generation is often higher, somewhat more expensive in cold winter nights with low wind.
If your car is your highest electricity draw, which is true for most EV owners, this is by far the single biggest saving available on Octopus Agile. No other behaviour change comes close.
The overnight charging mindset shift
The barrier to overnight charging is not technical. Every car supports it. Every charger supports it. The barrier is psychological.
The instinct to plug in and charge immediately when you get home is understandable. Range anxiety is real for new EV owners. The idea of going to bed with a half-empty battery feels uncomfortable until you have lived with the car for a few months and understand that you never actually need a full battery at 10pm. You need a full battery at 7:30am when you leave for work.
The departure time feature is designed precisely for this. Set your departure time, set your target charge level, plug in when you get home, and forget about it. The car is never actually charging during the expensive hours - it is just sitting there, connected, waiting for the overnight cheap window to begin. By morning, it is full. It is warm if you have set pre-conditioning. And you have spent £2.80 instead of £19.
The one window to always avoid is 4pm to 8pm. This is the universal peak on the UK grid. On Octopus Agile, this window is consistently two to four times more expensive than daytime rates and five to ten times more expensive than overnight rates. There is no scenario in which charging in this window makes financial sense when overnight charging is available to you.
If you commute in two different cars on alternate days, or have an irregular schedule, the smart charger approach is the most robust. Set a maximum departure time, let OHME or similar manage the cheap windows automatically, and the saving happens without any daily decision-making on your part.
The shift from instinct charging to departure-time charging is worth £400 to £600 a year. Every year. For as long as you own an electric car. That is the calculus. Three minutes of setup today buys you hundreds of pounds, annually, for the life of the vehicle.