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PHEVs produce almost five times greater planet-heating pollution than lab-reported data indicate, according to a new report.

Widening Gap Between Lab and Real-World Emissions

Data reveals that PHEVs emit just one-fifth lower CO₂ than conventional petrol and diesel cars, based on research conducted by a non-profit organization. That contrasts significantly with laboratory tests, which suggested a 75% decrease in pollution.

Analysts examined data from in-vehicle energy use meters 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 higher than official figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a senior researcher participating in the study. “That discrepancy is widening and creates a serious issue. Consequently, PHEVs pollute nearly as much as gasoline cars.”

Primary Factors Driving the Discrepancy

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

Additionally, when running in EV mode, emission levels were well above official estimates. That happened because EV motors were not strong enough to function independently, resulting to combustion motors burning gasoline for nearly one-third of the distance completed in electric mode.

Policy and Financial Implications

Based on calculations, the lowballing of PHEV CO2 output enabled several major automaker groups to avoid more than €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 more per year in operating expenses than would be estimated under lab conditions.

“The bold statements that automakers often promote about their PHEV cars are clearly far from the truth,” commented a transport analyst. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and saving money. Actually, PHEVs are little better than standard gas and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been drawn back into policy discussions as carmakers have pressed the EU to relax CO₂ standards. A proposed prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive sector and resistance from member states with significant car industries.

Several high-level politicians have proposed plug-in hybrids as a possible “flexibility” solution to introduce in the regulation.

An independent energy policy expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after a long period in which parts of the automotive industry argued there was insufficient data to accurately evaluate actual emissions.

“These findings show, without question, that the difference between official and actual PHEV energy use and CO₂ output is significantly greater than for gasoline or conventional cars,” they stated. “All policy adjustments concerning PHEVs should be made with extreme caution and considering this data.”