Monthly Archives: September 2015

What’s the impact on total CO2 emissions of electric cars or – are they really fossil fuelled?

The recent Volkswagen Diesel scandal has resulted in renewed debate around electric vehicles (EVs) and encouraged me to give some more thought to my feelings on them.

As usual I am interested in their use from a benefits to society/transport planning perspective rather than an individual consumer perspective – it may make perfect sense for individuals to get an EV depending on their circumstances.  However, while I consider that they may be a fix to significantly reduce air pollution in cities (although at least one, extremely thorough, study suggests that this is not clear cut, with some places in the US getting a disbenefit from electric car use in terms of air pollution) – they leave the host of other problems that come with motor vehicles including road danger, noise (most noise from motor vehicles being associated with tyres or the vehicle moving through the air, rather than engine noise), the road space requirements for them splitting communities and fail to deliver the exercise benefits of active travel – or public transport which frequently involves at least some active travel in every journey.  In addition to this, a large chunk of the particulates associated with motor vehicle usage actually come from wear and tear on tyres/brakes – these particulate emissions will remain whatever method propels the vehicle.

I am specifically interested in whether EVs will reduce carbon footprints over conventional vehicles.  If a government is worried about climate change, does it make sense to invest time, money and effort into promoting their use?

Other Analysis:

A quick dive into the available literature brings up a few different sets of analysis.  It seems that how effective they are at reducing (or not) CO2 emissions relative to conventionally powered motor vehicles is highly sensitive to the source of the electricity powering the EV.  What is interesting about all of the analysis I found is that it all assumes that adding an extra load on the electricity grid does not change the mix of electrical supply.  i.e. an increase in demand from electric cars increases the amount of renewable energy or efficiency of electricity production – on which more later.

Here’s a particularly clear graph which popped up, from this article here:

Screen Shot 2015-09-30 at 22.12.22

They also put together a neat little graph, re-scaling this into MPG equivalent which seems more intuitive to me.  On this scale, a petrol car which can achieve better than 30mpg is a better choice for reducing CO2 emissions than an electric car from a coal-heavy electricity mix.  The best modern petrol cars, when driven in an efficient manner, can deliver double this!

Emissions-Equivalent-Petrol-Car

According to this type of analysis, in the countries with the highest proportion of their electricity from renewables, it appears that an EV will beat a petrol car several times over.  In the UK, an efficient petrol or diesel car will just about beat an EV.  However, I think there are problems with using this type of analysis as it is based on a key assumption which I think is incorrect.

A Challenge to Previous Available Analysis

This analysis, and all the rest of the analysis that I could find in the time available to me for research are all based on the assumption that drawing more electricity from the grid does not change the supply mix.  When we look at the total supply of energy for the UK provided by the National Grid, it comes to a total of about 27.3 million tons of oil equivalents.  This compares with total demand for energy by the UK road network of 40 million tons of oil equivalent.  If we assume that most fuel is burnt on longer journeys which are not practical for EVs; and that we can only realistically aim for 1/8th of this energy usage being converted to electric vehicles, the additional demand on the grid is some 5 million tons of oil equivalent.

I do not know for certain, but it seems highly unlikely to me that adding this amount of energy demand on the national grid will have no effect on the energy mix.  Although there are complications around usage of pumped hydro to store electrical energy, and efficiency of power stations under sub-maximal loads, what seems most likely to me overall is that renewable sources (with 0 fuel cost, but high installation costs) get used first, and then fossil fuels are used to top this up (because the majority of the cost of these is in the consumption of the fuel, rather than in the construction of the facility).  This seems to be supported by the fact that it is reported that the electricity mix at night, when consumption is lower, has a higher proportion from renewable sources.

If this is the case, then any extra load on the grid over and above the current usage, will result in more fossil fuels being used.  Does it not seem reasonable to assume, therefore, that the extra electrical energy needed to fuel EV’s will come from fossil fuels?

If this is the case then extra EVs adding extra load on the national grid can be thought of as being fossil fuelled, resulting in them being far less efficient in terms of CO2 emissions than more efficient petrol or diesel cars once transmission and generation losses are accounted for.

Conclusion

  1. If we look back at the data above, it seems clear that *if my assumptions are correct*, that EVs produce many times more CO2 equivalent emissions than an efficient petrol vehicle, undermining the case for subsidising and promoting the use of these vehicles.
  2. It seems that until we have a surplus of renewable energy that this will remain the case.  A government interested in reducing the country’s carbon footprint should prioritise de-carbonising the grid over the use of electrical cars
  3. Although not the focus of this article, this argument has implications for individuals who may be interested in buying an electric car to try and reduce their carbon footprint (hint: you may be better off investing elsewhere – e.g. in solar panels or a wind turbine for your house)

Does anyone have any expertise on how the national grid works that might challenge or support the assumptions that I have made above?  Please do comment if so.

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