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Recharging Your Electric Car

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Driving a petrol, diesel or hybrid car creates CO2 because fossil fuels are burned when combustion engines are used.

But using an electric car doesn't mean that your driving is CO2-free.

Electricity for Recharging Electric Cars

Electricity for Recharging

Electric cars usually have a means of partiallly recharging the battery by capturing the energy created when braking the car.

In the main though, you need to recharge an electric car from the mains electricity supply.

Depending on weather conditions, between 40%-50% of the electricity generated in the UK is created by burning fossil fuels, which releases CO2, though the proportion of electricity from renewable sources is increasing.

If you've signed up to an electricity tariff that only involves power from renewable sources (or you are fortunate enough to recharge from a solar panel or wind turbine), you can pretty much claim to be recharging CO2-free.

But for the rest of us, recharging an electric car will still involve plugging in to mains electricity from the UK National Grid.

So, until the Grid is supplied 100% by renewable sources of electricity, recharging involves burning fossil fuels, which means your electric car recharge creates CO2.

But how much?

Calculating Electric Car Recharge CO2

We've calculated the CO2 likely to be released each year from the recharging of an electric car, assuming 10,000 miles travelled annually and electricity generated from burning fossil fuels.

We've based our calculations on;

• the manufacturer's claimed battery capacity of the car (this is measured in kilowatts of electricity per hour);
• the CO2 produced at the power station to create a kilowatt-hour (or 'KwH') of electricity for recharging;
• the distance ('range') the car could theoretically drive on a full battery charge.

Calculations of the CO2 produced by power stations burning fossil fuels vary, but a generally accepted level is 233grammes of CO2 discharged for every kilowatt-hour of electricity produced.

So, in our table for each car we've;

• multiplied battery capacity (Column C) by power station CO2 output per KwH of recharge time;
• divided the recharge CO2 output (D) by the battery range in miles (E);
• converted range to kilometres (F) so you can compare electric cars to petrol and diesel engines*;
• converted the CO2 output back to miles so you can see the CO2 impact of recharging for 10,000 miles per annum (G).

*CO2 output for cars is usually denoted in grammes per kilometre travelled.

We've based the car's battery range on the Worldwide Harmonised Light Vehicles Test Procedure, the 'official' measure of electric car battery range.

The result in Column G of the table is an estimate for the 'Carbon Footprint' of recharging an electric car for 10,000 miles of driving each year.

Remember that our figures ignore renewable sources of electricity - it's a worst case based on 100% fossil fuel power for electricity generating stations.

And if your annual driving is different to our 10,000 mile calculation, you can see the actual figures for each car based on your own annual mileage by clicking here.

What Is A Carbon Footprint?

A 'Carbon Footprint' represents the amount of carbon dioxide (CO2) produced by the goods or services we use or consume.

The CO2 output from an internal combustion engine (e.g. petrol, diesel or hybrid) is measured officially in the UK in Grammes Per Kilometre ('GP/Km') travelled, so we convert a vehicle's CO2 test results into Grammes Per Mile, then multiply this value by the user's annual mileage.

This gives the annual CO2 produced by the vehicle's exhaust, measured by weight in metric tonnes or kilogrammes (a metric tonne is approximately 1,000 kilogrammes or 2,205lbs - it's approximate because a gramme is a measure of mass rather than weight).

Remember that other lifestyle goods and services produce CO2 as well as vehicles with an internal combustion engine, and the figures produced by our carbon footprint calculation only relate to those for cars and vans.

Keep in mind too that the driving style of the car user will impact the number of times a car will need to be recharged each year and, for simplicity, we've assumed that the battery is discharged down to zero power then recharged back up to 100%.

Drivers of electric cars will usually recharge the battery well before it is completely discharged and may not charge it to 100% of capacity, but the overall effect of our calculation by battery capacity, range and total annual miles should still provide an accurate comparison.