While most hybrids are said to use one to two litres of fuel per 100km, a study claims they need six litres on average
Plug-in hybrid electric cars (PHEVs) use much more fuel on the road than officially stated by their manufacturers, a large-scale analysis of about a million vehicles of this type has shown.
The Fraunhofer Institute carried out what is thought to be the most comprehensive study of its kind to date, using the data transmitted wirelessly by PHEVs from a variety of manufacturers while they were on the road.
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According to the study, the vehicles require on average six litres per 100km, or about 300%, more fuel to run than previously cited.
The scientists of the Fraunhofer Institute found that the main reason for the higher-than-stated fuel usage was due precisely to the fact that the PHEVs use two different modes, the electric engine and the combustion engine, switching between both. Until now it has been claimed by manufacturers that the vehicles used only a little or almost no fuel when in the electric mode. The studies showed that this was not in fact the case.
On the assumption phevs have the combustion engine off unless they are in hybrid or performance mode:
I think it’s decisive because the article’s focus is fuel consumption but fuel consumption in phevs is actually just a proxy for driver behaviour. (Once you factor out differences between models)
So while the study does show that phevs technically have worse fuel economy in real world usage, it doesn’t show they use more fuel in either electric mode or in hybrid mode than previously believed.
The conclusion is useful for understanding the overall impact of phevs on petroleum consumption, air quality and global warming, but it’s misleading when evaluating what kind of car you should buy.
Since you know how you drive, learning new information about average driver behaviour doesn’t factor into your decision on what kind of car you buy.
The environmentally conscious answer is still no car if possible, electric if you need a car but most journeys fall within the range limit and phev if you need a car for frequent long range usage.
Tldr; it’s contentious because the article reports information useful for policy decisions to a general public who are making individual consumer decisions where the information is misleading.