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 or MyMPG in the U.S. The researchers furthermore 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 results: “On average, the real-world fuel consumption and CO2 emission values of plug-in hybrid vehicles for private drivers in Germany are more than twice as high as according to the official test procedure. For company cars, the deviation is even four times the official values.” As a result, the gap between official and real-world values is much larger for plug-in hybrid vehicles than for conventional combustion engine vehicles.

Underlying reason is the fact that plug-in hybrid vehicles often are not recharged regularly. Statistically, private users of vehicles in Germany re-charge their plug-in hybrid vehicle only on three out of four days. Company car users, on average, re-charge only every second day. The low frequency of recharging reduces the share of electric driving and thereby increases fuel consumption and CO2 emissions of plug-in hybrid vehicles in real-world driving. On average, private plug-in hybrid vehicles are driven only 37% of their mileage in electric mode; for company car vehicles it is only 20%.

The Fraunhofer ISI and ICCT researchers conclude concrete recommendations from their analysis. The European Commission should update the testing procedures for plug-in hybrid vehicles and limit any credits as part of the EU CO2 regulation for new cars to those plug-in hybrid vehicles that demonstrate a high share of electric driving in real-world. ICCT Director Dr. Peter Mock suggests that “National governments should provide fiscal incentives only for those plug-in hybrid vehicle models that offer a high electric range and limit the power of the built-in combustion engine”. Furthermore, any subsidies or reduced taxation rates should be tied to the vehicle owner demonstrating predominantly electric driving. Meanwhile, legal and financial barriers for installing home charging devices should be reduced.

But also vehicle manufacturers should take action: By increasing the electric range of plug-in hybrid vehicles, from today on average 50 kilometers to about 90 kilometers, and by meanwhile limiting the range of the built-in combustion engine, manufacturers can provide an incentive for drivers to regularly re-charge their vehicles and to drive predominantly with electricity. Fleet managers should limit the available budget for petrol or diesel tank cards and instead offer employees to re-charge plug-in hybrid vehicles easily and at low cost. In doing so, the share of electric driving for plug-in hybrid vehicles could be increased.

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