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Plug-in hybrid electric vehicles produce nearly five times more planet-heating pollution than lab-reported data indicate, as per a new analysis.

Growing Gap In Official and Real-World Emissions

Data reveals that PHEVs emit only one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to research carried out by a non-profit organization. This differs significantly with laboratory tests, which assumed a three-quarters reduction in pollution.

Analysts examined information from onboard energy use monitors of 800,000 vehicles sold in Europe between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a senior researcher involved in the study. “That discrepancy is widening and poses a significant problem. Consequently, PHEVs emit nearly as much as petrol cars.”

Primary Reasons Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to total distance. They found that just 27% of travel was done in electric mode, whereas lab assumptions assumed 84%.

Additionally, when running in electric mode, pollution amounts were well above lab estimates. This happened because electric motors were insufficiently powerful enough to operate alone, resulting to combustion motors burning fossil fuels for nearly a third of the distance covered in EV mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV emissions enabled four large carmaker groups to escape more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay about €500 more per year in running expenses than would be assumed under lab conditions.

“The bold claims that manufacturers like to make about their PHEV vehicles are obviously way off the mark,” commented a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are helping the planet and cutting money. Actually, PHEVs are little improved than standard gas and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been drawn again into political discussions as carmakers have pressed the European Union to weaken CO₂ targets. A proposed ban on sales of new combustion engine cars in 2035 has faced intense lobbying from the automotive sector and resistance from member states with large automotive manufacturing.

Several senior politicians have suggested PHEVs as a possible “flexibility” solution to introduce in the regulation.

One external energy economics expert, who was unaffiliated with the research, described the analysis a “highly valuable addition” after a long period in which parts of the automotive industry argued there was too little information to properly assess real-world emissions.

“The results demonstrate, without question, that the difference in lab and real-world PHEV energy use and CO₂ emissions is significantly larger than for petrol or conventional vehicles,” the expert stated. “Any policy adjustments regarding PHEVs should be made with extreme care and in the light of that data.”