From time to time we have considered the aspects of doing ìThe Extra Mileî from the perspective of hybrid and electric cars, and it’s time to update the picture. Plug-in hybrids have become more plentiful and, if we are truly economy-minded and not blinkered by diesel power, we should look at the potential appeal of such cars, and in what circumstances they may be viable alternatives to diesel. In view of our commitment to eco cars, there’s also the possible attraction of the latest economical petrol vehicles, of which a number are listed in our data pages, where they meet our criteria of carbon dioxide emissions of 100g/km or below. Finally, we need to look at pure electric cars, and whether their increasing range makes them a serious contender.

Trawling the Real MPG figures collected from owners by our good friend Honest John, (honestjohn.co.uk/realmpg) there’s no clear advantage for hybrids in fuel economy terms. We can see typical figures for hybrids that have comparable diesel model variants (Toyota Yaris and Auris) where the mpg differences are less than five per cent either way. The picture is perhaps a little clearer with diesel power versus ìecoî petrol power (Peugeot 308, Volkswagen Polo and Golf, Vauxhall Corsa), where the differences clearly still favour diesel, by margins ranging from 5mpg to 15mpg. Nor do petrol city cars, like the up!, the Mii, and the Citigo, or the Fiat 500 really threaten the economy of diesels, with fuel economy returns of at best 50 to 60mpg, which is the same sort of figure that you can get from many larger and far more spacious diesels, although we have to accept the high capital cost of smaller diesels, and the almost total absence of true diesel city cars.

Looking at plug-in hybrids, the picture is cloudier, as the nature of any owner’s normal motoring determines what proportion can be covered using electric power. Buyers have been tempted by the Mitsubishi Outlander PHEV, with the promises of 166.1mpg for the combined official economy figure, but the 58mpg mixed motoring owner average is somewhere between as a best of 70 to 80mpg on local runs, using lots of electric power, and motorway cruising when you’ll be lucky to better 35mpg, depending on your cruising speed. In contrast, Toyota Prius plug-in owners report an overall average of an impressive 95mpg, but then it’s vastly less capacious than the Outlander, but fine aerodynamics do mean a Prius can cruise on the motorway on petrol power alone at 55 to 60mpg.

Pure electric cars are represented in significant numbers by the Nissan Leaf and Renault Zoe, and we cannot source mpg equivalent figures for real life ownership. What we know is that each kWh of electricity will generally take these, and similar cars like a Volkswagen e-Golf, between three and five miles in normal duty. With electricity sourced at optimum tariffs (domestic night rate charging), that means maybe as little as 10p to cover 3 to 5 miles, or around 2p to 3p per mile. At today’s carbon equivalents for UK power generation, it equates to somewhere between 35g/km and

55g/km of carbon dioxide, or less than half that of a typical diesel hatchback. At best then, pure electric cars are very clean and economical. At the other extreme, in fast motorway cruising, with full heating or air conditioning, using electricity purchased on-road at relatively high cost, and with the significant heat losses of fast charging, that can become more like 10p a mile. We are still looking at a good diesel car being just as efficient as any electric car for longer journeys, and without time lost for charging en route, the stress of range anxiety, and finding a charging point that is available when you need one.

So, we might argue, the diesel car is far from dead, or even on the way out. We could be a long time waiting for a practical, long range, electric alternative to a large diesel MPV or SUV carrying seven people, or five people and significant cargo, such as a Volkswagen Touran 2.0 TDI delivering 45mpg plus, or a Jaguar F-Pace clocking 40mpg plus. Or a modest CitroÎn C4 Grand Picasso returning 50mpg in day-to-day use ñ all figures gleaned from real owners at Honest John’s Real MPG site.

Victor Harman