For their statistical analyses, the researchers made use of anonymized data that vehicle drivers had voluntarily reported to online portals, such as Spritmonitor in Germany. The researchers also took into account data on company cars that had been provided by fleet managers.

Dr. Patrick Plötz, Coordinator of the Business Unit Energy Economy at Fraunhofer ISI and lead author of the study, summarizes one of the key findings: "On average, the real-world fuel consumption and CO₂ emission values of plug-in hybrid vehicles for private drivers in Germany and other European countries are about three times as high as according to the official test procedure. For company cars, the deviation is even about five times the official values." This gap between official and real-world values is much larger for plug-in hybrid vehicles than for conventional combustion engine vehicles. The real-world fuel consumption for private plug-in hybrids is at about 4.0 to 4.4 liters per 100 kilometers. In the case of company cars, the average values are between 7.6 to 8.4 liters. Average fuel consumption according to the official test procedure is between about 1.6 to 1.7 liters per 100 kilometers. Every additional liter of gasoline burnt is not only expensive but also corresponds to an exceedance of the emission levels defined in the EU-wide CO₂ standards for new vehicles.

The real-world gap of plug-in hybrids continued to grow

In comparison to a previous Fraunhofer-ICCT analysis from 2020, the real-world gap of plug-in hybrids continued to grow. "Plug-in hybrids that are certified according to the new WLTP tend to have an even higher discrepancy than older vehicle models that were certified according to the NEDC.", says Dr. Georg Bieker, one of the co-authors fo the study. Every year the gap between official and real-world fuel consumption and CO₂ values increases by about 0.1 to 0.2 liters per 100 kilometers, the researchers conclude from the data analysis. On average, privately used plug-in hybrids are driven largely electric only for about 45% to 49% of their mileage, and for company cars the share is as low as 11% to 15%.

The Fraunhofer ISI and ICCT researchers offer concrete recommendations from their analysis. "Fiscal incentives, such as purchase premiums and a reduced company car tax, should be tied to demonstrating a electric share of about 80% or a fuel consumption of 2 liters per 100 kilometers during real-world driving," recommends ICCT Director Dr. Peter Mock. Furthermore, the utility factor—which defines the assumed electric drive share in WLTP—should be adapted to the average real usage patterns of plug-in hybrids. As part of a recent policy initiative, the European Commission proposes exactly such an adaptation. In the long term, the CO₂ emissions of plug-in hybrid vehicles prevent the EU from achieving a climate neutral transport sector. As foreseen in the European Commission’s proposal for the future CO₂ emission standards, no new plug-in hybrids should be registered beyond the year 2035. An important vote by the Environment Ministers of all EU member states on this regulation is expected for June 28.

The Fraunhofer Institute for Systems and Innovation Research ISI analyzes the origins and impacts of innovations. We research the short- and long-term developments of innovation processes and the impacts of new technologies and services on society. On this basis, we are able to provide our clients from industry, politics and science with recommendations for action and perspectives for key decisions. Our expertise is founded on our scientific competence as well as an interdisciplinary and systemic research approach.