Plug-in hybrid electric vehicles (aka PHEVs) are a popular choice among those who want to reduce their carbon footprint but are not yet ready to make the full commitment to all-electric vehicles.
But a previous assumption by regulators like the European Union that PHEVs emit 75% less carbon than gasoline and diesel-dependent cars is actually false, according to researchers from Brussels-based non-profit Transport & Environment who studied hundreds of thousands of cars registered in Europe between 2021 and 2023.
In a new study published on Thursday, the researchers claim that plug-in hybrids actually only emit 19% less than cars with internal combustion engines.
“I think it’s quite a scandal to have this gap between real world and official data,” one of the co-authors of the study, Yoann Gimbert, told Gizmodo.
That gap has also been widening over the years. In 2021, PHEVs actually emitted 3.5 times the official emissions estimates. By 2023, that number was nearly five times.
There are several reasons why this could be the case, according to Gimbert.
The first is that plug-in hybrid owners, at least Europeans, might not be using the cars in their intended way. Both plug-ins and standard hybrids rely on both an electric motor and an internal combustion engine. But, unlike standard hybrids, plug-in hybrids have a larger battery. As the name suggests, this allows them to be plugged in to charge externally and to drive some distances while relying entirely on the electric motor.
Gimbert said that European drivers might not be incentivized to drive it fully in electric mode. This could be due to things like a lack of fast charging capability or relatively lower power of the electric motor, he says. This gap is shown in the data as well when you look at something called “the utility factor,” which is the ratio of miles that a car travels in electric mode over the total travel distance. It’s used by EU estimates as well.
Official EU estimates had the utility factor of PHEVs penciled in at over 84%, but the researchers found that it was much lower at just 27%.
And even with the utility factor completely accounted for, the real-life to estimate gap still exists. That’s because plug-in hybrids are never fully electric, Gimbert said.
Even in electric mode, the car continues to rely partially on hybrid mode. That is, the researchers found that PHEVs are not designed to operate fully in electric mode: the internal combustion engine still provides significant additional power and burns fossil fuels for at least one-third of the way when driving in electric mode. The engine especially assists the electric motor while accelerating, driving at higher speeds, or going uphill.
“It’s actually 68 grams of CO2 per kilometer in electric mode, instead of being zero emission,” Gimbert said. The number is nine times higher than the 8 grams per kilometer estimated by the EU’s methodology. “That’s something that is often not really expected by consumers,” he added.
“Frequent reliance on the combustion engine means many PHEVs emissions are no better than many conventional hybrids or petrol cars,” the researchers concluded.
The EU has announced some corrections to its measure of the utility factor, and is getting ready to review its carbon emissions standards for cars completely next year. Researchers say that the corrections are a good start, but real-world emissions will still be 18% higher than official figures without a full review of the standards.
But the European automotive industry stands against it. German Association of the Automotive Industry (VDA) is lobbying to cancel the corrections, keep the current methodology, and roll back a controversial ban on new combustion engine cars in the EU by 2035, Gimbert said.
According to the researchers, the underestimation of carbon emissions from plug-in hybrids has helped major automakers like Volkswagen, Mercedes-Benz, and BMW to avoid roughly €5 billion (a little under $6 billion) in fines between 2021 and 2023. The EU has strict fleet-average carbon emissions targets for automakers.
If the auto industry’s lobbying efforts succeed, the researchers claim it can result in a 64% increase in the carbon emitted by 2050 under current EU regulations.
“PHEVs are not fitted for 100% emission reduction by 2035,” Gimbert said.
Across the pond, Americans are growing less interested in electric vehicles than their European counterparts as EV prices continue to soar high in the U.S., especially in the absence of the electric vehicle tax credit. The American Automobile Association thinks consumers might show more interest in hybrids and plug-in hybrids as electric vehicle demand continues to wane. But according to preliminary data from earlier this year, while demand for hybrid cars is soaring, plug-in hybrid demand, at least for now, is pretty much stagnant.