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Plug-in hybrid electric vehicles produce almost five times more planet-heating emissions than lab-reported data show, according to a new report.

Widening Gap In Official and Real-World CO2 Output

Statistics shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, according to analysis carried out by a non-profit organization. This contrasts sharply with lab tests, which assumed a three-quarters decrease in pollution.

Researchers studied data from in-vehicle energy use monitors of eight hundred thousand vehicles sold in Europe from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Real-world emissions are increasing, while official figures are decreasing,” stated a lead analyst participating in the report. “This gap is widening and poses a significant problem. Consequently, PHEVs pollute almost as much as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts linked the majority of the gap to overestimates of the “utility factor” – the percentage of kilometers driven in electric mode relative to total distance. The team found that just 27% of driving was done in EV mode, whereas official estimates assumed over four-fifths.

Additionally, when operating in EV mode, pollution amounts were significantly higher than lab projections. That happened because EV motors were insufficiently powerful enough to operate alone, leading to engines burning gasoline for nearly a third of the distance completed in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output enabled four major automaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay about €500 extra per year in running costs than is estimated under laboratory conditions.

“The strong statements that automakers like to make about their PHEV cars are clearly far from the truth,” commented a automotive analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have lately been drawn again into policy discussions as carmakers have pressed the EU to weaken CO₂ targets. A planned ban on sales of new combustion engine cars in 2035 has faced heavy lobbying from the automotive sector and opposition from EU countries with large car manufacturing.

Some high-level officials have suggested plug-in hybrids as a potential “flexibility” option to introduce in the regulation.

One external energy policy specialist, who was unaffiliated with the research, called the analysis a “highly valuable contribution” after years in which segments of the automotive sector argued there was insufficient data to properly assess actual CO2 output.

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