Tuesday, 17 April 2007

Saab Biopower

A quick post while stuck on the ground at Heathrow waiting to go to Germany to try some Audis.

Today's Indy carries the write-up of our fuel consumption test of Saab's 9-5 BioPower. Since Saab and Ford introduced cars to the UK market last year that are capable of running on E85, a blend of 85% bioethanol and 15% petrol, there has been a certain amount of discussion of the pros and cons of this fuel, which is available at a small but growing number of branches of Morrisons. On the one hand, E85 has a higher octane rating and a modest price advantage (usually 2p per litre). On the other, it delivers fewer mpg.

Estimates of the exact size of this penalty vary enormously, so we decided to do a test - the answer that we came up with was that Saab's 9-5 BioPower suffers an 18% mpg penalty when running on E85 over a wide range of road conditions. We did plan a more elaborate test involving two cars running in parallel, one on E85 and one on unleaded, but after months of trying, we just couldn't get two directly comparable cars together at the same time, so we settled for running a single car in one direction on E85 and then retracing our route on unleaded - not ideal, but hopefully fairly representative.

I've been following this subject for over a year now, and the more I look into it, the more complicated it seems to get. Official CO2 emissions data, for example, just look at tailpipe emissions for cars running on unleaded, not what is sometimes called the well-to-wheel impact, or the impact over the whole life of a car. That means cars running on E85 get no official credit for using a renewable fuel that has a built-in carbon offset in the form of the CO2 absorbed by the crops that are used to produce bioethanol. Take another example, the hybrid Toyota Prius, which delivers a very low tailpipe CO2 figure of 104g/km. What about the amount of energy that is used in manufacturing this immensely complicated car? What about the disposal of the large numbers of heavy batteries hybrids use?

I'm off to a day-long conference on the subject at Imperial College on Friday, which I hope will help me understand this a bit better. I'm not really expecting to come back with clear answers, though, just more insight into how complicated the whole thing is and why.

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