Why Electric Cars are Really Coal Cars

5 April 2011

by Professor Chris Rhodes

I saw a wonderful play at the Royal Court Theatre in London recently: "The Heretic" by Richard Bean. In a nutshell, the plot centres on a female academic, Dr Diane Cassell, who is researching sea-level rise. She finds none at some measurement point in the Maldives, but realises that both land and sea are rising together. Thus, while sea-levels are indeed rising, the islanders are unlikely to be forced from their lands by them. If she publishes her results, the department stands to lose a very lucrative contract from an insurance company and so her Head of Department forbids her to go public which she does, and on national television at that, so getting fired from her job. The Human Resources person is grimly hilarious.

In the play, one of her students with utterly green credentials including eating lots of garlic to apparently curb his own bodily greenhouse-gas emissions, refuses to go on a field trip in the university minibus on the grounds that it runs on fossil fuels, preferring instead to cycle forty miles there and forty miles back.

Diane asks him: "In your green future, how would we get fourteen students fifty miles to the North Yorkshire Weather Station?"
He replies: "There should be like an electric car/minibus. Electric cars don't have any emissions."
Diane responds: "Electric cars should be called coal cars. 30% of our energy comes from coal. Electricity is not naturally occurring in nature."

Now this does raise an issue about the "cleanliness" of electricity, which is all the more salient in view of the U.K. government's aim to install thousands of electric charging points around the country for electric cars with the aim to "wean us off imported oil". However, the majority of electricity in the U.K. is generated using power stations fired by coal (28%) and gas (45%), and hence even if a substantial substitution of the present 30 million British oil-fuelled cars by electric vehicles could be made, it would entail the consumption of vast quantities of these other fossil fuels instead to provide the additional electricity for them.

It is claimed in a Royal Academy of Engineering (RAE) report on electric cars that they are in any case cleaner because 80 - 90% of the energy put into them in terms of electricity is recovered in terms of useful power at the wheels, to be compared with 20 - 30% in a conventional oil-powered car. Well, that sounds good, but the reality is that only about one third of the energy in the coal or gas actually ends-up as electricity because of the Second Law of Thermodynamics and the Carnot Cycle limit - the other two thirds being thrown away as heat. Thus the electric car is harvesting in terms of well-to-wheel miles only about 27% of the original fossil fuel energy, so not that much better than the standard car running on petrol or diesel. The difference is merely whether about the same quantity of waste heat energy is thrown away at source or in the vehicle.

The green energy company, Ecotricity refers to electric cars as "wind-cars", to stress that they could run on electricity made from green sources such as wind. Indeed, the U.K. has made the decision to focus on wind-energy to meet its carbon-emissions targets, and plans to build offshore wind-farms on an impressive scale to do the job. It is advised by the Committee on Climate Change that by 2020, 1.7 million electric cars should be on Britain's roads, or just over 5%, which I don't honestly see would make a serious hole in our demand for imported crude oil. 


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