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PHEVs emit nearly five times more planet-heating pollution than lab-reported data show, according to a recent analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs emit just one-fifth less CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a non-profit organization. This contrasts sharply with lab tests, which suggested a 75% 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 real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” stated a senior analyst involved in the report. “This discrepancy is widening and creates a significant issue. Consequently, PHEVs emit almost as much as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery mode relative to overall mileage. The team determined that just a quarter of driving was completed in EV mode, whereas lab estimates suggested over four-fifths.

Additionally, when running in EV mode, pollution amounts were significantly higher than official estimates. This occurred because EV motors were insufficiently powerful enough to operate alone, resulting to combustion motors using gasoline for almost one-third of the travel completed in EV mode.

Regulatory and Financial Implications

According to estimates, the underestimation of PHEV emissions enabled several major automaker companies to avoid over €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs could pay about €500 more per year in operating expenses than would be assumed under laboratory conditions.

“The strong claims that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the truth,” commented a transport analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly better than standard gas and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been brought again into policy debates as automakers have lobbied the European Union to relax CO₂ targets. A planned prohibition on sales of new internal combustion cars in 2035 has faced heavy pressure from the car sector and opposition from member states with significant car industries.

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

An external energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after a long period in which parts of the car sector claimed there was insufficient information to properly assess actual emissions.

“The results demonstrate, without question, that the difference in official and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for petrol or conventional cars,” they said. “Any regulatory changes concerning PHEVs should be implemented with utmost care and considering that evidence.”