EVs v Fossil fuel vehicles: which is more efficient?
EBN reader – and engineer – Rod Cripps contributed this article on EVs, posing the question on energy efficiency.
The purpose of this article is to compare from the point of view of energy efficiency,
It takes into account the total energy cycle for both energy sources, as most comparisons decry electric on the basis that they are “really driven by coal”, assuming that the electricity comes from coal, but they totally ignore the embedded energy costs of petrol and diesel before it gets to the bowser.
The whole article is based on efficiency, which is the engineering measure of the proportion or percentage of the total energy which is actually doing useful work. The rest is losses. It refers to practical vehicles, not hypothetical. The information sources wherever possible have been official industry sources or reviewed, published academic papers. This hasn’t been possible in all cases, and I have had to use some internet sources.
The terms and units used are: Electric energy – watt.hour or Kilowatthour,
Fuel Energy Efficiency
Fossil fuels have to be pumped from wells, or dug up as shale, or oil sands or tars, transported to a refinery somewhere, refined, and then shipped to distribution terminals in each country before finally being transported to the service station tanks.
Fortunately, good information is available as far as getting it to distribution terminals in the USA.
The energy cost to get fossil fuel from extraction, transport, refining and into distribution tanks is globally equivalent to 23.2% of the energy value of the final fuel. Thus the efficiency is overall 76.8%
These costs were based on the USA market, so the transport component would be higher for Australia. The transport component of this figure is about 5%, so the additional cost for Australian markets is probably more like 7%, giving a total efficiency figure of 74.8%
The final delivery from terminals to bowser, including losses and leakage, in energy terms is 1.2% on the best figures I can find, thus an efficiency of 98.8%
Combining these two figures gives an Earth to Bowser efficiency of 73.9%
I am sure that will come as a surprise to most people – over one quarter of the fuel is lost before it gets to your petrol tank!!! For every 3 litres you buy, you are paying for another one lost along the way. Remember we are talking about efficiency here not necessarily actual fuel although that is effectively where most of the lost energy comes from.
Of course the best source of electrical energy for electric vehicles would be from solar sources wherever you are recharging. If you include wind (winds are generated by solar heat), this is not entirely far fetched. The source may not be right on your doorstep but should not be a great distance away. In this case of course, the energy efficiency can be regarded as 100%, as it is not captured electrical energy which is being lost through solar panel inefficiencies.
In Australia as a whole power generation efficiency is:
The Proportion of hydro is 4.9% Aust wide (Tasmania. 66%), the proportion of other renewables such as wind and solar is 7.6%
This gives an average Australia wide generation efficiency of 53.7% (Tasmania 86.9%)
Australia wide transmission/distribution efficiency is 94.95% – say 95%
Thus the total efficiency is .95 x .537 = 50.9% (Tasmania 82.6)
If we now account for the efficiency of the battery charger, (97.5%) we get a final figure for
Electrical Energy, from Source to Battery: 49.6%. (Tasmania. 80.5%)
Car Engine Efficiency
Car engine efficiency is more slippery than a cake of soap in a spa bath. It depends on petrol versus diesel, is the engine working hard or running light, who is driving, and a lot of other things as well, so I can only use generally accepted industry averages. (By the way, don’t equate performance with efficiency, as a high performance engine may well be less efficient then lower performance ones. It is often the losses which enhance the performance). It is generally also true that engines made specifically for use over limited rev ranges and power loading are much more efficient than ones which must operate over all ranges. Thus the engines in hybrid cars are more efficient than those in normal cars generally.
BY Rod Cripps