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Plug-in hybrid cars release almost 5x greater planet-heating emissions than lab-reported data indicate, as per a new report.

Growing Gap Between Lab and Real-World CO2 Output

Statistics reveals that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, according to research carried out by a non-profit organization. That differs significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers studied information from onboard fuel consumption meters of eight hundred thousand cars sold in the EU from 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, up from 3.5 times in 2021.

“Actual emissions are rising, while official emissions are falling,” stated a senior analyst participating in the study. “That gap is widening and poses a significant problem. As a result, PHEVs emit almost as heavily as gasoline vehicles.”

Key Factors Driving the Discrepancy

Researchers attributed the majority of the difference to inflated estimates of the “utility factor” – the ratio of miles travelled in battery power relative to total mileage. The team found that only a quarter of travel was done in electric mode, whereas official estimates suggested 84%.

Additionally, when running in electric mode, pollution levels were significantly higher than lab estimates. This happened because electric motors were insufficiently powerful sufficient to operate alone, resulting to combustion motors burning gasoline for nearly one-third of the distance completed in electric mode.

Policy and Economic Implications

Based on estimates, the lowballing of PHEV emissions allowed four large carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 more per year in running costs than would be estimated under laboratory tests.

“The strong claims that automakers often promote about their PHEV vehicles are clearly way off the truth,” stated a transport analyst. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly better than regular gas and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the car industry and opposition from member states with large automotive industries.

Several high-level politicians have suggested plug-in hybrids as a potential “compromise” option to include in the regulation.

One independent energy policy expert, who was not involved with the research, called the analysis a “very useful contribution” after years in which parts of the car sector claimed there was insufficient data to accurately evaluate actual emissions.

“The results show, beyond any doubt, that the difference in official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or diesel vehicles,” the expert said. “All regulatory adjustments concerning PHEVs should be made with utmost caution and in the light of that data.”