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Plug-in hybrid electric vehicles release almost five times greater planet-heating pollution than official figures show, according to a recent report.

Widening Discrepancy In Lab and Real-World Emissions

Data reveals that PHEVs emit just 19% less CO₂ than conventional gas and diesel vehicles, according to analysis conducted by a non-profit organization. This contrasts sharply with laboratory estimates, which suggested a three-quarters reduction in emissions.

Analysts studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars sold in Europe from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” stated a senior researcher participating in the study. “This gap is widening and poses a serious issue. As a result, PHEVs pollute almost as much as petrol cars.”

Primary Reasons Driving the Emissions Gap

Analysts attributed the majority of the gap to overestimates of the “utility factor” – the percentage of kilometers travelled in electric power relative to total distance. They determined that just 27% of driving was completed in electric mode, whereas lab estimates suggested 84%.

Additionally, when operating in EV mode, emission amounts were well above lab estimates. That occurred because electric motors were not strong enough to function alone, leading to engines using gasoline for nearly one-third of the travel completed in electric mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled several large automaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs would spend approximately €500 extra per year in running expenses than would be estimated under laboratory conditions.

“The strong claims that automakers often promote about their PHEV cars are clearly far from the truth,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are helping the planet and cutting money. In reality, PHEVs are little improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought again into political discussions as carmakers have pressed the EU to relax CO₂ standards. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and opposition from EU countries with large automotive manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “compromise” option to include in the regulation.

An independent energy policy expert, who was not involved with the study, described the analysis a “highly valuable contribution” after a long period in which segments of the automotive sector claimed there was insufficient data to accurately assess real-world CO2 output.

“These findings demonstrate, without question, that the difference in lab and actual PHEV energy use and CO₂ output is significantly larger than for petrol or diesel cars,” the expert stated. “Any policy adjustments concerning PHEVs should be made with utmost care and in the light of that data.”