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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.
The cars involved were all produced between 2021 and 2023. The data transmitted enabled analysts to determine their precise and real-world fuel consumption, as opposed to that stated in the vehicles’ official EU approved certification.
PHEVs, cars which combine a petrol or diesel engine with a battery-powered electric motor that is charged from an external energy point, give drivers the flexibility to be able to switch between the ecologically safer power source, and the more conventional, but environmentally more damaging one, as and when conditions allow. Manufacturers typically market the vehicles as energy efficient. On paper at least, the vehicles are said to use much less fuel, between one and two litres per 100km, than conventional cars. However environmental groups have long since voiced scepticism over the claims.
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.
Patrick Plötz of the Fraunhofer Institute told German broadcaster SWR they suspected that the combustion engine in PHEVs is triggered to turn on far more frequently than previously thought. German-manufactured PHEVs were among those with the highest average fuel consumption, with the high-end Porsche model performing worst.
Plötz urged regulators to use the real-world emissions data. “Then one could say a manufacturer who does not comply with the (emissions) limits on the road may have to pay a penalty,” he said.
Porsche hybrids consumed more fuel – around seven litres per 100km – than other PHEVs when the electric motor kicks in, and significantly more than non-PHEVs in combustion engine mode. The lowest fuel consumption levels were found in the cheaper end of the PHEV market, in Kia, Toyota, Ford and Renault vehicles, which often used under one litre per 100km, or as much as 85% less fuel than the Porsche.
Asked by SWR, which published the results of the study on Wednesday, how to explain the discrepancy, Porsche referred to “differing usage patterns”, which it said influenced fuel consumption. Porsche insisted its fuel consumption measurements were in line with legal requirements, stating: “The fuel consumption figures of our vehicles are based on the legally prescribed EU measurement procedures.” These, it said, ensured “uniform and comparable values across Europe”.
“Deviations from individual real-world consumption figures can arise due to different usage profiles and external conditions,” such as road conditions, or driver behaviour, the company told SWR.
The scientists have called on EU regulators to adjust their measurements to fit the real-world findings, urging stricter controls as to how fuel consumption of plug-in hybrids is measured. According to the findings, the CO2 limits a car manufacturer’s fleet of vehicles is allowed to emit on average needs to be urgently adjusted.
Contacted by SWR, the EU Commission, which is responsible for CO2 limits, declined to comment on the findings.
The German Association of the Automotive Industry said it believed that existing measures to determine fuel consumption and CO2 emissions were reliable.
