We’ve often wondered the true environmental footprint of electric cars and while it is common knowledge that such cars are not really ‘zero emission’, it is difficult to find a full and reliable assessment of their real emissions.
However one firm has come to the rescue, environmental accounting firm Ecometrica has calculated that on average, an electric car powered by the UK standard electricity mix has a carbon footprint of around 75g/km CO2-lower than any petrol or diesel car currently available.
Gary Davis, Operations Director and chief greenhouse gas (GHG) analyst at Edinburgh-based firm calculated the figure based on the manufacturers’ range and battery capacity data for three electric cars; the Nissan Leaf, the Mitsubishi i-Miev and the Renault Fluence to give an equivalent to a car’s miles per gallon figure (but in this case is kWh/km).
Then Mr Davis took government data on the UK grid carbon intensity and applied this to the electric car efficiency. This grid carbon intensity calculation even included the energy losses at the power station and the energy losses for transmission and distribution across the UK grid.
The results gave an average of 75g/km CO2 travelled in an electric car, lower than the lowest emission diesel currently available (smart fortwo CDi at 86g/km) and low enough for electric cars to still qualify for exemption from the London Congestion Charge and UK road tax even with their emission figures accounted for.
As low as 3g/km CO2?
With an average combustion car figure of 208 gCO2/km, according to government data, electric cars appear along way ahead.
If the UK achieves its projections for grid average carbon intensity of 22.6 g/kWh of CO2 by 2050, electric cars (based on current efficiencies) would be as low as 3 g/km CO2.
While this sounds amazing, it does not account for the ‘upstream’ emissions associated with electric production. So the firm calculated this too; making a full ‘well to wheel’ analysis that current 75 gCO2/km figure increases to 85 gCO2/km. If the g/km figure for diesel and petrol cars included the same full analysis, a car currently labelled as 99g/km would actually have emissions of 118g/km and a car labelled 159g/km would see its figure increase to 187 g/km respectively.
A well-to-wheels analysis like this can be taken further still by asking about the relative emissions associated with manufacturing of a traditional combustion engine car versus an electric car and its batteries. While the report does not attempt to assess this complex and detailed question, it notes that manufacture of a vehicle tend represent 15 per cent to 20 per cent of a vehicle’s “lifetime” emissions-so now small amount.
Finally, the report concludes that on average, an electric vehicle is seven times more efficient than a petrol car and four times more efficient than a diesel car, thanks mainly to its fewer energy losses, principally because there are fewer moving parts in an EV; an electric car has about four main moving parts compared to an internal combustion engine car with over 300.
However the energy analysis is sensitive and is altered when the thermal inefficiency of the power station is included in which case an electric car might prove less efficient than the best diesels…
Full report: Technical paper
