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Plug-in hybrid electric vehicles produce nearly five times greater planet-heating emissions than lab-reported data show, according to a recent analysis.

Widening Discrepancy Between Official and Actual Emissions

Data reveals that PHEVs release just one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis carried out by a advocacy organization. This differs significantly with lab tests, which assumed a 75% decrease in emissions.

Analysts examined data from in-vehicle energy use monitors of 800,000 vehicles registered in Europe from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, increased from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported emissions are falling,” said a senior analyst involved in the report. “This discrepancy is growing and poses a significant issue. As a result, PHEVs pollute almost as heavily as petrol cars.”

Primary Factors Behind the Discrepancy

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery mode compared to total distance. They determined that just 27% of driving was done in EV mode, whereas lab estimates assumed 84%.

Even, when running in EV mode, emission amounts were significantly higher than official estimates. This happened because EV motors were insufficiently powerful sufficient to operate alone, leading to engines burning gasoline for nearly one-third of the distance covered in electric mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed several large automaker companies to avoid more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would spend about €500 more per year in operating costs than is assumed under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV vehicles are obviously far from the truth,” commented a automotive expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly improved than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have lately been drawn back into political discussions as carmakers have pressed the EU to relax CO₂ standards. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the car industry and opposition from EU countries with significant car industries.

Some high-level politicians have proposed PHEVs as a possible “compromise” solution to include in the legislation.

One external energy economics specialist, who was not involved with the study, described the analysis a “very useful contribution” after a long period in which segments of the automotive industry argued there was insufficient data to properly evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional cars,” they said. “Any policy changes concerning PHEVs should be implemented with extreme care and in the light of this data.”