Electric vehicles are zero-emission at point of use. However, emissions are produced during the generation of electricity, the amount depending on the method of generation. Therefore, the emissions need to be considered on a lifecycle basis so as to include power station emissions.
For greenhouse gases (such as CO2), electric cars charged using average UK 'mains' electricity show a significant reduction in emissions – the figures suggest a reduction of around 40% compared to an small petrol car (tailpipe 130 gCO2/km).
However, if an electric car is compared with a fuel-efficient diesel car (tailpipe 99 gCO2/km), the life cycle carbon benefit for an electric car using average 'grid' electricity is around 25% – a smaller but still significant reduction.
The reduction in carbon emissions is mainly due to the fact that electric cars are more energy efficient than conventional vehicles. So-called 'regenerative braking', which returns energy to the battery when the brakes are applied, also improves fuel efficiency by up to 20%.
Larger carbon reductions are likely as the UK grid continues to 'decarbonise'. Of course, if renewable or 'green tariff' electricity is used, then lifecycle greenhouse gas emissions are effectively zero.
For regulated emissions, including nitrogen oxides (NOx) and particulates (PMs), electric cars using average 'mains' electricity are increased. However, as these are emitted from power-stations which are well away from urban areas, their overall impact tends to be much less than when emitted from the exhausts of petrol and diesel cars.
As is the case with greenhouse gas emissions, if renewable electricity is used, then lifecycle regulated emissions are also virtually eliminated.
While electric vehicles can provide significant climate change benefits, reduce noise pollution, and reduce use of fossil fuels, they can also increase levels of air pollutants leading to higher rates of acidification, and may increase the potential impact on human health in areas where resources (such as lithium) are extracted for battery production. Indeed, the sourcing of lithium remains contentious relating to the level of reserves and the local impacts on human health where lithium is mined.
Taken overall, and given that current road transport is responsible for significant emissions of nitrogen oxides and particulate matter, the impact on human health is likely to be reduced within urban areas, well away from the centres of battery production, due to the fact that most ULCVs are zero-emission at the point of use.
The life cycle carbon emissions for a typical electric car using the average UK mix electricity are around 100 gCO2/km. This is based on the current UK electricity mix with an avaregae emissions factor of around 500 gCO2/kWh. Comparing this with the emissions for a small new car of 130 gCO2/km, adding a 15% real world correction, plus an additional 15% for upstream fuel production emissions, the average lifecycle for new cars is approximately 170 gCO2/km. This implies a reduction in lifecycle CO2 emissions of around 40%. Using a 99 gCO2/km model as a comparator, the estimated lifecycle carbon benefit for a BEV is almost halved to around 25%.
Preparing for a life cycle CO2 measure. Report by Ricardo on behalf of Low Carbon Vehicle Partnership, May 2011.
Market delivery of ultra-low carbon vehicles in the UK. Report by Ecolane on behalf of RAC Foundation, January 2011.
Strategies for the uptake of electric vehicles and associated infrastructure implications, ElementEnergy (for The Committee on Climate Change). Final Report, October 2009.
Investigation into the Scope for the Transport Sector to Switch to Electric Vehicles and Plug-in Hybrid Vehicles. Arup & Cenex (for BERR & DfT), 2008.
Investigation into the Scope for the Transport Sector to Switch to Electric Vehicles and Plug-in Hybrid Vehicles. Arup & Cenex (for Department for Business Enterprise and Regulatory Reform & Department for Transport), October 2008.