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PHEVs release nearly 5x greater planet-heating emissions than official figures show, according to a new analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs release only 19% less CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a non-profit group. That differs sharply with laboratory estimates, which assumed a 75% decrease in pollution.

Researchers studied information from in-vehicle energy use monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a lead researcher participating in the study. “This gap is growing and creates a significant problem. As a result, PHEVs pollute almost as much as petrol cars.”

Primary Factors Driving the Emissions Gap

Analysts attributed most of the gap to overestimates of the “utility factor” – the ratio of kilometers driven in electric power compared to overall mileage. The team found that just a quarter of driving was completed in EV mode, whereas official assumptions assumed 84%.

Additionally, when running in electric mode, emission amounts were significantly higher than official projections. That happened because EV motors were not strong sufficient to function alone, leading to combustion motors using gasoline for nearly one-third of the distance completed in electric mode.

Policy and Economic Implications

Based on estimates, the lowballing of PHEV emissions enabled several large carmaker companies to escape over €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs would spend about €500 more annually in operating costs than would be estimated under lab tests.

“The strong statements that automakers like to make about their PHEV cars are clearly far from the truth,” commented a automotive analyst. “Buyers are being misled into believing that by buying a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little better than standard gas and diesel cars in terms of fuel use, CO₂ production, and running costs.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have lately been drawn again into policy discussions as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced intense pressure from the car sector and opposition from EU countries with significant car manufacturing.

Some senior politicians have proposed PHEVs as a possible “compromise” option to introduce in the regulation.

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

“These findings demonstrate, beyond any doubt, that the difference in official and actual PHEV energy use and CO₂ output is much, much larger than for petrol or conventional cars,” they said. “Any policy changes regarding PHEVs should be implemented with extreme caution and in the light of that evidence.”