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Plug-in hybrid electric vehicles release almost five times more planet-heating pollution than lab-reported data indicate, according to a recent analysis.

Widening Gap Between Official and Actual Emissions

Statistics reveals that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel vehicles, based on research carried out by a advocacy organization. That contrasts sharply with lab estimates, which assumed a three-quarters reduction in emissions.

Analysts studied data from onboard energy use meters of eight hundred thousand cars registered in Europe from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, increased from three and a half times in 2021.

“Actual emissions are rising, while lab-reported emissions are decreasing,” said a senior researcher involved in the report. “This discrepancy is widening and creates a serious problem. As a result, PHEVs pollute almost as much as petrol cars.”

Key Factors Driving the Discrepancy

Analysts attributed the majority of the gap to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to overall distance. They determined that only 27% of driving was done in EV mode, whereas official estimates suggested over four-fifths.

Additionally, when operating in electric mode, emission amounts were well above lab projections. This occurred because electric motors were insufficiently powerful enough to function independently, resulting to combustion motors burning fossil fuels for almost one-third of the distance covered in electric mode.

Regulatory and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output allowed four major automaker companies to escape more than €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs would pay approximately €500 extra per year in running costs than is estimated under lab conditions.

“The bold statements that manufacturers often promote about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are little improved than regular petrol and diesel vehicles in terms of energy use, CO₂ production, and operating costs.”

Political Discussion and Automotive Lobbying

Hybrid cars have recently been brought again into political debates as carmakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on sales of new internal combustion cars in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with large automotive manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “compromise” solution to include in the legislation.

One independent energy economics specialist, who was not involved with the research, described the analysis a “highly valuable contribution” after years in which segments of the car sector argued there was too little data to accurately assess real-world CO2 output.

“These findings show, beyond any doubt, that the difference in lab and actual PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel cars,” the expert stated. “All policy changes concerning PHEVs should be implemented with extreme caution and in the light of this data.”