Overview
2011 is being hailed as the year of the electric car, or certainly the year that the electric car becomes available to the general public for everyday use. There are a host of new electric cars entering the market in 2011 and 2012 and every major car manufacturer now has plans to introduce an electric vehicle in the next three years. We all know that an electric vehicle has zero tailpipe emissions and the popular counter argument is usually “what about the emissions at the power station?”
This technical paper by Gary Davis, Operations Director at Ecometrica, answers that question by presenting a definitive figure of gCO2/km for U.K. electric cars when CO2 emissions at the power station are taken into account. Based on a range of electric cars that you can buy in the U.K. this year and next, the average emissions are 75 gCO2/km.
This figure is lower than any other car in production today, including the Toyota Prius (89 gCO2/km) and VW Golf Bluemotion (99 gCO2/km), two of the incumbent best performing low emission vehicles in the “small family” class of car. For reference, the government figure for CO2 emissions from an average U.K. car is 208 gCO2/km. If emissions from the power station were included in official gCO2/km figures, electric cars would still qualify for exemption from the London Congestion Charge and U.K. road tax.
How did we calculate this?
Firstly, we calculated electric car efficiency, which is a measure of how much electricity is required to power an electric car for every mile it drives. In essence, this is equivalent to a car’s miles per gallon figure (but in this case is kWh/km). This was done based on manufacturers’ range and battery capacity data for three electric cars; the Nissan Leaf, the Mitsubishi i-Miev and the Renault Fluenz.
We then took government data on the U.K. grid carbon intensity, which is a measure of the CO2 emissions produced for every kWh of electricity consumed in the U.K., and applied this to our electric car efficiency. We ensured that in our grid carbon intensity calculations, we included not only the energy losses at the power station, but also the energy losses for transmission and distribution of the electricity across the U.K. electric grid. It’s worth noting that we carried out this calculation on the basis of CO2 only, deliberately omitting the other greenhouse gases (GHG) that are produced at the power station, so that the result could be compared to existing car manufacturers’ data on a like-for-like basis, since these also omit other GHGs.
Is this figure the same in all countries?
No. Electric grid carbon intensities vary from country to country because the proportion of coal, oil, gas, nuclear and renewable generation is different in each country. This means our electric car in the U.K. will have a different gCO2/km figure if charged and driven in another country. The chart below shows this effect for a number of countries and compares the electric vehicle results to modern diesel and petrol powered cars. You can see that diesel and petrol cars have the same emissions irrespective of which country they are in, whereas the electric car emissions vary depending on the country in which it’s used.
The chart shows that in Greece and China, an average electric car would emit more CO2 at the power station, than modern diesel vehicles. This is because most of the power stations in China and Greece are coal fired, which is the most carbon intensive form of electricity generation. The electric grids in the U.K. and U.S.A. are made up of a range of coal, oil, gas, nuclear and renewable power stations and produce a similar carbon intensity to each other, and in turn, a similar gCO2/km figure for electric cars. In France, the electric grid is mainly fed by nuclear power stations, resulting in a very low carbon intensity, and in Canada, the reason for low carbon intensity is a very high proportion of renewable power generation from hydro-electric power stations [1].
This also demonstrates that as governments move to clean up their grids by replacing carbon intensive power stations with lower carbon intensity sources of generation, then electric cars will see their equivalent gCO2/km figure drop too. The U.K. Government projections are for the grid average carbon intensity to drop to 22.6 gCO2/kWh by 2050, which would mean that the emissions associated with electric cars (based on current efficiencies) would be as low as 3 gCO2/km.
What happens if we include the emissions associated with manufacturing the fuels that go into the power station?
The effect of adding in these so called “upstream” emissions sources is that our 75 gCO2/km figure increases to 85 gCO2/km. If we do the same thing for diesel and petrol cars, so that we can continue comparing on a like-for-like basis, we see that the figures increase from 99 to 118 and 159 to 187 gCO2/km respectively.
