When to Charge Your Electric Vehicle in Great Britain for Lowest Carbon and Cost
Electric vehicles emit zero CO2 from the tailpipe. But the electricity that charges them carries a carbon cost that varies enormously depending on when you plug in. Charge at the right time, and your EV is close to genuinely zero-carbon. Charge at the wrong time, and it may be producing more CO2 per mile than some hybrids.
Understanding when to charge — and why — is one of the most impactful things an EV owner can do.
The Carbon Reality of EV Charging
The headline carbon figure for EVs uses an average grid carbon intensity. For Great Britain in 2025, that average is roughly 180–220 gCO2/kWh. A typical EV with efficiency of 4 miles per kWh would emit around 45–55 gCO2 per mile — already significantly lower than the 120–150 gCO2/mile of an average petrol car.
But "average" masks enormous variation:
| Charging time | Typical carbon intensity | CO2 per mile (4 mi/kWh EV) |
|---|---|---|
| Midday, sunny/windy | 50–80 gCO2/kWh | 12–20 gCO2/mile |
| Overnight, windy | 80–120 gCO2/kWh | 20–30 gCO2/mile |
| Winter weekday evening | 250–350 gCO2/kWh | 62–87 gCO2/mile |
Charging your EV at a winter peak evening is roughly the same carbon footprint as a modern efficient diesel. Charging at a summer midday can cut emissions to roughly the same as a bicycle.
The goal is simple: shift your charging to low-intensity windows whenever possible.
The Three Best Charging Windows
1. Overnight on Windy Nights (Best Consistent Option)
For most EV owners, overnight charging is the default — and it's often the best choice. Here's why:
- Demand drops significantly overnight, reducing competition for grid capacity
- Offshore wind farms continue generating through the night (wind doesn't sleep)
- Gas peaking plants are mostly off — reducing the marginal carbon intensity
- Many home chargers have built-in scheduling — set it and forget it
Optimal window: 11pm–6am, with intensity typically 80–150 gCO2/kWh depending on wind conditions.
On a genuinely windy night (which UK weather frequently delivers), carbon intensity can drop to 50–80 gCO2/kWh between midnight and 5am — genuinely low-carbon charging.
2. Solar-Peak Midday (Spring to Autumn)
From March through September, the GB grid benefits from significant solar output between 10am and 2pm. On clear days with 15+ GW of solar, carbon intensity can drop to 50–100 gCO2/kWh.
If you work from home, or have a workplace charger, daytime charging in summer is often the greenest option — potentially even lower carbon than overnight charging if wind conditions are calm.
This is also when you're most likely to benefit from your own rooftop solar panels if you have them — effectively charging your car from sunshine directly.
3. Periods of High Wind, Any Time of Day
Carbon intensity tracks wind generation more closely than any other single factor. On a very windy day — and Great Britain has many of them — intensity can stay below 100 gCO2/kWh throughout the entire 24-hour period. In these conditions, timing matters less; it's a good day to charge at any time.
Check the Generation Mix to see how much wind is on the system right now.
The Worst Time to Charge
Winter weekday evenings, 5pm–8pm, are consistently the worst time to charge your EV in Great Britain:
- Electricity demand peaks as millions of people arrive home simultaneously
- Solar output is zero (it's dark before 5pm in winter)
- Wind may or may not be generating — there's no guarantee
- Gas peaking plants are dispatched at full capacity to fill the gap
- Carbon intensity is at its daily maximum: often 250–350 gCO2/kWh
Plugging your EV in when you arrive home at 6pm on a January evening and letting it charge at full power is the single worst charging habit for carbon. It also contributes to grid stress during the period when capacity is most constrained.
Using the 48-Hour Forecast for Smart Charging
The key tool for EV owners is the 48-hour carbon intensity forecast. Published by the Carbon Intensity API and displayed on GB Power Insights, it shows the predicted gCO2/kWh for every half-hour period over the next two days.
Here's how to use it in practice:
- Check the forecast the evening before — look at tonight's overnight window and tomorrow's midday window
- Identify the lowest-intensity windows — these show as green in the forecast
- Schedule your charger to start during those windows
- Allow enough hours — a 7kW home charger will add around 25–30 miles per hour, so a 200-mile charge needs roughly 8 hours from near-empty
Most smart EV chargers (Ohme, Indra, Pod Point, Zappi) can accept a schedule based on a start time and end time, with target SOC. Set it to charge during the green window.
View the 48-hour carbon forecast →
Octopus Agile: Let the Market Do the Work
If you're an Octopus Agile customer, you have the best possible arrangement for low-carbon, low-cost EV charging. Agile prices update every 30 minutes and reflect the actual wholesale electricity market, which tracks closely with carbon intensity.
- When carbon is low (wind/solar abundant) → Agile prices are low (often 5–15p/kWh)
- When carbon is high (gas-heavy evenings) → Agile prices are high (25–50p/kWh)
The Ohme charger with Agile integration will automatically charge your EV during the cheapest overnight slots — effectively doing the optimisation for you. The saving compared to peak-rate charging can be £400–800/year for a typical EV driver.
GB Power Insights shows live Octopus Agile prices alongside carbon intensity in the Market Prices view, so you can see both dimensions together.
Workplace Charging: An Underrated Opportunity
If your employer has workplace EV chargers and you work typical office hours (9am–5pm), this is actually an excellent charging opportunity:
- You're likely drawing some solar during the working day
- Daytime carbon intensity is lower than evening
- Charging during work hours avoids the home evening peak entirely
Many large employers now offer free or subsidised workplace charging as a benefit. If yours does, prefer this to home charging unless you can reliably charge overnight.
Public Rapid Charging
Rapid chargers (50–150 kW DC) charge much faster but the timing is usually out of your control. A few points:
- Motorway service station chargers are often used during peak driving periods (late afternoon/early evening) — unfortunately coinciding with high carbon intensity
- If you have flexibility on a long journey, consider charging at midday (lower carbon and sometimes lower prices) rather than the late afternoon
- Some rapid chargers are now connected to behind-the-meter renewable generation or backed by renewable PPAs
Summary: The EV Charging Hierarchy
- Best: Overnight on windy nights, scheduled via smart charger (11pm–6am)
- Good: Midday in spring/summer with solar peak, especially from your own rooftop PV
- Acceptable: Any high-wind period with sub-100 gCO2/kWh intensity
- Avoid where possible: Winter weekday evenings 5–8pm
- Ideal setup: Octopus Agile + smart charger + automatic overnight scheduling
The right time to charge your EV can vary every day. The 48-hour carbon forecast takes the guesswork out of it.