The advice offered on this page regarding improving fuel economy is primarily directed towards drivers of conventional diesel cars, the vast majority of our readership. But that’s not to suggest that the same principles do not apply in most ways to petrol-driven cars, and similarly all hybrids.
But much of the fuel-saving work is done for you when you’re driving a hybrid. Their energy recovery systems cleverly recycle energy normally lost as heat in braking for battery recharging, and even in conventional cars the smart alternators now often used are programmed to raise the battery charge level during braking, thereby reducing the alternator’s drain on engine power at other times. Depending upon the type of motoring involved though, the advantages of a hybrid are extremely variable and most struggle to show real advantages over well-driven conventional diesels in most extra-urban driving, or any kind of sustained high speed cruising. If you’re a sales representative or businessman covering 40,000 miles a year on Britain’s motorways and dual-carriageways, any hybrid will still struggle to match the fuel economy of a well-driven diesel. Recent figures from tests by other publications report a Golf GTE plug-in (petrol) hybrid that’s returning a disappointing 55mpg, as compared with an Audi A3 1.6 TDI, tested by our friends at Audi Driver magazine, that recorded over 62mpg in their full test, including performance testing, and nearly 78mpg when driven for economy.
Let’s dig a bit deeper and look at the figures for hybrids and EVs, in relation to both fuel economy and emissions. A quick survey of some figures declared by the owners of eight popular hybrids shows an average economy of the order of 55 to 60mpg which, we suggest, is easily matched by many diesels. Few reliable figures are available for an equivalent fuel economy for today’s plug-in electric vehicles but, barring maybe the Tesla and possibly range-extender plug-ins with a supporting small petrol engine, none of such alternative transport is really suitable for any high-mileage business driver or many commuters. Real-life mixed motoring economy figures available for electric vehicles suggest figures of between 2.5 to 4.0 miles covered per kWh of electricity, (typically 12p per kWh – free charging electricity cannot last!) and thus costing 3 to 5p per mile, compared with 8 to 12p a mile for diesel.
The significant cost benefit of electric vehicles comes from the lack of excise duty on electricity (and how long can that growing loss of tax revenue last?) and the zero urban emissions that address the problems of urban pollution, particularly of nitrogen oxides and particulates. The carbon footprint of Britain’s power station electricity is around 320g/kWh, but improving, with the progressive closure of coal-fired power stations; this converts to carbon dioxide emissions of around 50 to 60g/km at the power station for running a Renault Zoe or Nissan Leaf, and less than half the real life emissions of comparable hatchbacks. Such figures are, however, dependent upon what powers the electricity generation, and in some countries, like Norway and Canada, electric vehicles are already a very solid and ultra-clean proposition for urban transport, whilst in some states of the USA and in China, electric vehicles are simply as dirty as their primarily coal-fired power stations, and that’s pretty dirty!
We should also consider the carbon dioxide emissions derived from manufacture of the lithium-ion battery packs that are standard equipment for most electric vehicles. Over a forecast 100,000 mile life of an EV lithium-ion battery pack, the emissions equate to the order of 3 to 10g/km of carbon dioxide, depending on battery range and vehicle weight. However, most electric vehicles, at present, are likely to be used on low mileage semi-urban duties, and it’s more realistic to consider the picture over ten years at a lower average annual mileage of 2,500 to 5,000 miles, or 10 to 20 miles per working day. The spin-off from 800,000 grams of carbon dioxide manufacturing emissions over 25,000 to 50,000 miles in ten years, then rises to between 10 to 20g/km, but will fall as battery technology continues to improve.
Let us not forget that the urban conditions where electric vehicles shine, public transport is often a more sensible alternative, and when taxis are eventually all converted to being emissions-free, there may be little reason to take a car into many cities. But there’s a good case for more focussed government incentives to encourage taking older, dirty, urban duty diesels, and particularly light commercials, off the road, to replace them with hybrids and electric vehicles. But the picture is vastly different for medium to high-mileage non-urban cars where, as yet, there are really no practical emissions beating, and cost-saving, alternatives to the latest clean Euro-6 diesels, particularly when 65 to 75mpg fuel economy is apparently achievable, with some effort by the driver.
Victor Harman
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One Response
The article by Mr Harman propagates the error concerning the exhaust emissions levels latest “clean” Euro 6 specification diesel cars, the official tests post the revelations from the USA os September 2015 show that in real world driving conditions, a typical Euro 6 diesel car is non-compliant for Nox emissions by a factor of 8, in other words a Euro 6 diesel car is polluting at 8 times the rolling road lab test and each diesel car is has a pollution footprint equivalent to 10 petrol cars.
This fact destroys the argument by Mr Harman for the case for a diesel car over a petrol car such as the Prius