A major real-world analysis of around one million plug-in hybrid electric vehicles (PHEVs) has found they use significantly more fuel than manufacturers claim, raising concerns about emissions reporting and environmental impact.
The research was conducted by Germany’s Fraunhofer Institute and analyzed real-world driving data transmitted wirelessly by vehicles produced between 2021 and 2023. Unlike lab-based certification tests, this dataset reflects actual driving behavior and fuel usage on roads, according to The Guardian.
The study found that plug-in hybrids consume an average of about six litres of fuel per 100 kilometers. That is roughly three times higher than the one to two litres per 100 kilometers typically claimed in official manufacturer figures.
Plug-in hybrids combine a battery-powered electric motor with a petrol or diesel engine. They are marketed as efficient because they can operate in electric mode without burning fuel. However, the analysis showed that the combustion engine activates far more frequently in real-world driving than expected.
Researchers believe this frequent switching between electric and combustion modes is the primary reason for the higher fuel consumption. In many cases, drivers rely on the petrol engine more often than assumed in official efficiency calculations.
Fuel consumption varied widely depending on the model and manufacturer. High-performance plug-in hybrids, such as Porsche models, recorded some of the highest fuel usage at around seven litres per 100 kilometers. Meanwhile, more affordable models from brands like Kia, Toyota, Ford, and Renault showed lower fuel consumption in some cases.
Manufacturers maintain that their official fuel consumption figures comply with European Union testing procedures, which are designed to provide standardized and comparable results. They say differences between official figures and real-world usage can be influenced by driving style, road conditions, and charging habits.
Researchers are now urging regulators to incorporate real-world vehicle data into emissions assessments. They argue that relying solely on laboratory test results may underestimate actual fuel consumption and carbon emissions.
The findings could have significant implications for climate policy, vehicle regulations, and how plug-in hybrids are classified as low-emission vehicles. Plug-in hybrids have been promoted as a transitional technology between traditional combustion engines and fully electric vehicles, but their real-world efficiency may be lower than expected.