Readers letters
Mike Travers has pointed out a mistake and raised a point that I overlooked in my earlier letter (Letters PE October) regarding the efficiency of electric cars. He also suggests that manufacturing battery powered cars produces significantly more CO2 than manufacturing a conventional car. I have now corrected the mistake and included heater losses in the overall energy budget for a battery car.
The data for electricity generation efficiency was obtained from the IEA Energy Balances relating to 2007 and I incorrectly applied the ‘Own Use’ and ‘Distribution Losses’ quoted in these tables. In 2007, the generating efficiency, across all energy sources, for the UK was 35.9%, and for France was 30.3%.
I overlooked the heating requirements for electric cars, which will significantly reduce the battery range and hence the energy conversion efficiency. From a couple of battery car reviews, it appears that heating the car reduces the range by 25% to 40%. On this basis it is a reasonable penalty of 33% for heating appears to be appropriate.
Energy recovery during coasting and braking will provide some battery recharge; this is likely to provide sufficient energy for lights and other ancillaries.
The corrected figures for an electric car running in the UK are 5.4 kW.h of fuel energy, 4.3 kW.h of fossil fuel energy and 1,000 g CO2 per kW.h of traction energy.
For a car running in France the corrected figures are 6.4 kW.h of fuel energy, 0.6 kW.h of fossil fuel energy and 190 g CO2 per kW.h of traction energy.
I am not sure that the corrections make much difference to the case for or against electric cars. The real argument is whether we need to develop alternatives to the internal combustion engine for our personal transport. The threat of climate change and our present reliance on finite reserves of fossil fuels suggest that we do!
With electric cars, the emissions can be controlled by changing the energy mix used to generate electricity; this is possible in the medium to long term. With conventional cars, the only way to reduce the emissions significantly is to replace our existing fuels with bio-fuels. With total UK fuel consumption for road transport in 2007 of more than 17 million tonnes of petrol and 20 million tonnes of DERV this will be a very difficult over any period!
Regarding Travers’ final point, it is probably true that the CO2 emissions released during manufacture of a battery car are significantly greater than for a conventional vehicle. However, with the right electricity generating energy mix, this is quickly overtaken by the savings during the vehicles life. This may be one reason that the one of the first major manufacturer to commit to a range of battery cars is French.
Initially, the battery car will probably remain the preserve of the rich and famous, or the committed green; much as the motor car was the preserve of the rich and famous in the late 19th and early 20th Century. How things changed in the succeeding decades!
Robin Trow, Snodland, Kent
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