Doing your part
Electric drive trains are generally more efficient than combustion engines. Typically petrol and diesel engines utilise 25-30% of the fuel’s energy at best. Recent figures from the RAC (2010) show typical energy use for electric vehicles of 0.6 MJ/km as compared to hybrids (1.2 MJ/km) and diesels (1.7 MJ/km). Some electric vehicles also use ‘regenerative braking’, which tops up the battery when the brakes are applied – this can increase vehicle range by as much as 20%.
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 CO2 emissions, electric cars charged using average UK ‘mains’ electricity show a significant reduction – the figures suggest a reduction of around 40% compared to an small petrol car . However, if an electric car is compared with a fuel-efficient diesel car, the lifecycle carbon benefit for an electric car using average ‘grid’ electricity is around 25% – a smaller but still significant reduction.
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.
Also looking forward a large number of Electric Vehicles attached to the grid might serve as storage for energy production, especially renewables, to smooth out the generating requirement.
One new impact gaining increasing attention is the energy required to manufacture an EV, which is significantly more than for a conventional vehicle. So far, the studies show that, taken overall, for an average vehicle, the life cycle emissions are still reduced. One recent report by Ricardo (2011) concludes that the life cycle carbon benefit is currently around 20% – this benefit will increase over time as more renewable electricity becomes available.
For regulated emissions, including nitrogen oxides (NOx) and particulates (PMs), electric cars using average ‘mains’ electricity 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.