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Plug-in hybrid cars release almost 5x greater planet-heating pollution than official data indicate, according to a new report.

Widening Discrepancy Between Lab and Real-World Emissions

Data reveals that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, based on research carried out by a non-profit organization. This contrasts sharply with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts studied information from onboard energy use meters of 800,000 vehicles sold in Europe from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while official emissions are decreasing,” stated a senior analyst involved in the report. “This discrepancy is widening and creates a significant issue. As a result, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Behind the Emissions Gap

Analysts linked the majority of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in battery power relative to overall mileage. They found that just a quarter of travel was completed in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when running in EV mode, pollution levels were well above lab estimates. That happened because electric motors were insufficiently powerful enough to operate alone, resulting to engines 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 allowed several large automaker groups to avoid over €5bn in penalties between 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could spend about €500 more annually in operating expenses than is assumed under laboratory tests.

“The bold claims that automakers like to make about their plug-in hybrid cars are obviously far from the truth,” stated a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly improved than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Automotive Pressure

Hybrid cars have recently been drawn back into political discussions as carmakers have lobbied the EU to relax CO₂ targets. A planned prohibition on new combustion engine cars in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant automotive manufacturing.

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

One independent energy policy specialist, who was not involved with the research, called the analysis a “highly valuable contribution” after a long period in which parts of the automotive sector argued there was too little data to properly evaluate actual CO2 output.

“The results show, beyond any doubt, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or conventional cars,” the expert stated. “Any policy adjustments regarding PHEVs should be implemented with utmost caution and in the light of this data.”