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Plug-in hybrid electric vehicles release almost 5x more planet-heating pollution than official figures indicate, according to a recent analysis.

Growing Discrepancy In Official and Real-World CO2 Output

Statistics shows that PHEVs emit only one-fifth lower CO₂ than conventional petrol and diesel cars, based on analysis conducted by a non-profit organization. That contrasts sharply with laboratory tests, which assumed a 75% reduction in pollution.

Researchers studied information from in-vehicle energy use meters of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are falling,” stated a lead analyst participating in the report. “This discrepancy is widening and creates a significant problem. Consequently, PHEVs emit almost as heavily as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts attributed the majority of the difference to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery power compared to total mileage. The team determined that just 27% of driving was completed in EV mode, while official estimates assumed over four-fifths.

Even, when operating in electric mode, emission levels were well above official estimates. That occurred because electric motors were not strong enough to function alone, leading to combustion motors burning gasoline for almost a third of the distance covered in EV mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed four large automaker groups to escape more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs could pay approximately €500 more per year in running costs than is assumed under laboratory tests.

“The strong claims that manufacturers often promote about their PHEV vehicles are clearly far from the mark,” commented a automotive expert. “Buyers are being duped into thinking that by buying a PHEV, they are helping the environment and saving money. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the European Union to relax CO₂ targets. A planned prohibition on new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and opposition from member states with significant car manufacturing.

Some high-level politicians have suggested PHEVs as a potential “flexibility” option to introduce in the regulation.

An external energy policy specialist, who was not involved with the research, called the analysis a “highly valuable addition” after years in which segments of the car sector claimed there was insufficient information to properly assess real-world CO2 output.

“The results show, beyond any doubt, that the gap between official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel cars,” the expert said. “All regulatory adjustments regarding PHEVs should be implemented with extreme care and in the light of this evidence.”