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Plug-in hybrid electric vehicles produce almost 5x greater planet-heating emissions than official data indicate, according to a new analysis.

Growing Gap In Lab and Actual Emissions

Statistics shows that PHEVs release just 19% lower CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a non-profit group. That differs sharply with lab tests, which suggested a three-quarters decrease in emissions.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 vehicles registered in Europe between 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab estimates, up from 3.5 times in 2021.

“Actual emissions are rising, while official emissions are falling,” stated a senior researcher participating in the study. “That gap is growing and poses a significant issue. As a result, PHEVs emit nearly as much as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the percentage of miles driven in battery mode relative to total distance. The team determined that only 27% of travel was done in EV mode, while official assumptions suggested over four-fifths.

Additionally, when operating in electric mode, emission amounts were significantly higher than official estimates. This occurred because EV motors were not strong enough to operate independently, resulting to engines using gasoline for nearly one-third of the travel completed in EV mode.

Policy and Economic Implications

According to calculations, the underestimation of PHEV CO2 output allowed several large automaker companies to avoid more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 extra per year in running expenses than would be estimated under laboratory conditions.

“The strong claims that manufacturers often promote about their plug-in hybrid cars are obviously way off the truth,” commented a automotive analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are little better than regular petrol and diesel vehicles in terms of energy consumption, CO₂ emissions, and running costs.”

Political Debate and Automotive Pressure

Hybrid cars have recently been drawn again into political discussions as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced heavy pressure from the automotive sector and resistance from member states with significant automotive industries.

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

One external energy policy expert, who was not involved with the study, described the report a “very useful addition” after years in which segments of the automotive industry argued there was too little data to properly evaluate actual CO2 output.

“These findings demonstrate, without question, that the gap in lab and real-world PHEV energy use and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” the expert said. “Any regulatory adjustments regarding PHEVs should be made with extreme care and in the light of this evidence.”