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Plug-in hybrid cars release nearly 5x greater planet-heating emissions than lab-reported data indicate, according to a new analysis.

Growing Discrepancy Between Official and Real-World CO2 Output

Data reveals that PHEVs emit just one-fifth lower CO₂ than conventional gas and diesel cars, based on analysis conducted by a non-profit organization. This differs significantly with lab estimates, which assumed a 75% reduction in emissions.

Analysts studied information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in Europe from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from three and a half times in 2021.

“Actual emissions are rising, while official emissions are falling,” said a lead researcher involved in the study. “That gap is growing and creates a significant issue. Consequently, PHEVs pollute almost as much as petrol cars.”

Primary Reasons Behind the Discrepancy

Researchers linked most of the difference to overestimates of the “utility factor” – the ratio of miles travelled in battery power compared to total mileage. They determined that just a quarter of travel was done in EV mode, whereas lab estimates assumed over four-fifths.

Additionally, when running in EV mode, emission amounts were well above official estimates. That happened because EV motors were insufficiently powerful sufficient to function independently, resulting to engines using gasoline for almost a third of the travel completed in EV mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV emissions allowed several large carmaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs would pay about €500 extra annually in operating expenses than is assumed under lab conditions.

“The strong claims that manufacturers like to make about their plug-in hybrid cars are clearly far from the truth,” stated a automotive expert. “Consumers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of energy consumption, CO₂ emissions, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have recently been brought again into political debates as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the automotive sector and opposition from EU countries with significant automotive manufacturing.

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

An external energy policy specialist, who was unaffiliated with the research, described the analysis a “very useful contribution” after years in which parts of the automotive sector claimed there was too little data to accurately assess real-world emissions.

“The results show, beyond any doubt, that the gap in lab and actual PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional vehicles,” the expert said. “All regulatory adjustments regarding PHEVs should be made with extreme caution and considering this data.”