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Plug-in hybrid electric vehicles produce nearly five times more planet-heating emissions than lab-reported figures indicate, as per a recent analysis.

Growing Discrepancy Between Lab and Actual Emissions

Statistics shows that PHEVs emit only one-fifth lower CO₂ than conventional gas and diesel vehicles, based on analysis conducted by a advocacy organization. That differs significantly with lab estimates, which suggested a three-quarters reduction in emissions.

Researchers studied data from onboard energy use monitors of 800,000 vehicles registered in Europe from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while official figures are falling,” stated a lead researcher participating in the study. “This discrepancy is growing and poses a serious issue. As a result, PHEVs pollute almost as much as petrol cars.”

Key Reasons Driving the Emissions Gap

Researchers attributed most of the difference to inflated estimates of the “utility factor” – the ratio of miles driven in battery power compared to total distance. The team determined that just 27% of travel was completed in electric mode, whereas lab assumptions assumed 84%.

Even, when running in electric mode, emission amounts were significantly higher than lab estimates. That happened because electric motors were not strong sufficient to function independently, leading to engines burning fossil fuels for almost one-third of the travel covered in electric mode.

Policy and Economic Consequences

Based on estimates, the underestimation of PHEV CO2 output allowed several large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ standards.

Furthermore, drivers of PHEVs could pay approximately €500 more per year in operating costs than would be estimated under laboratory tests.

“The bold claims that automakers often promote about their plug-in hybrid vehicles are obviously far from the truth,” commented a transport expert. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are only slightly better than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have recently been brought again into policy debates as carmakers have pressed the European Union to relax CO₂ standards. A planned prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive industry and opposition from EU countries with significant automotive industries.

Some high-level officials have proposed PHEVs as a potential “flexibility” option to include in the regulation.

One external energy policy specialist, who was not involved with the study, called the analysis a “highly valuable addition” after years in which segments of the car industry argued there was too little data to accurately assess actual emissions.

“These findings demonstrate, without question, that the difference in official and real-world PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel vehicles,” the expert stated. “Any policy changes regarding PHEVs should be implemented with extreme caution and considering that evidence.”