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Plug-in hybrid cars produce nearly 5x more planet-heating emissions than lab-reported data show, according to a recent analysis.

Growing Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel cars, based on research conducted by a non-profit group. That contrasts significantly with laboratory estimates, which suggested a 75% reduction in emissions.

Researchers examined information from onboard energy use meters of 800,000 vehicles registered in the EU from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual emissions are rising, while lab-reported emissions are falling,” said a senior analyst participating in the report. “This gap is widening and creates a significant problem. As a result, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts attributed most of the difference to inflated estimates of the “utility factor” – the ratio of miles driven in battery power relative to total mileage. They found that just a quarter of travel was completed in electric mode, whereas lab assumptions suggested 84%.

Additionally, when running in EV mode, pollution levels were well above official projections. That happened because EV motors were not strong enough to operate independently, leading to combustion motors using gasoline for almost a third of the distance covered in electric mode.

Regulatory and Financial Implications

According to calculations, the lowballing of PHEV CO2 output allowed four major carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ standards.

Furthermore, drivers of PHEVs could spend about €500 extra per year in operating costs than is assumed under lab tests.

“The bold statements that automakers like to make about their PHEV cars are clearly way off the truth,” stated a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have recently been drawn again into political discussions as carmakers have lobbied the EU to relax CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced intense pressure from the automotive sector and opposition from EU countries with significant automotive manufacturing.

Some high-level politicians have suggested plug-in hybrids as a potential “flexibility” solution to include in the legislation.

An external energy policy expert, who was not involved with the study, called the report a “highly valuable addition” after years in which segments of the car sector argued there was insufficient information to accurately assess real-world emissions.

“These findings demonstrate, without question, that the difference in official and actual PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional cars,” they said. “All regulatory adjustments regarding PHEVs should be implemented with extreme care and considering that evidence.”