The Impact of WLTP on the Official Fuel Consumption and Electric Range of Plug-in Hybrid Electric Vehicles in Europe

Plug-in Hybrid Electric Vehicles (PHEVs) are one of the main technology options for reducing vehicle CO2 emissions and helping vehicle manufacturers (OEMs) to meet the CO2 targets set by different Governments from all around the world. In Europe OEMs have introduced a number of PHEV models to meet their CO2 target of 95 g/km for passenger cars set for the year 2021. Fuel consumption (FC) and CO2 emissions from PHEVs, however, strongly depend on the way they are used and on the frequency with which their battery is charged by the user. Studies have indeed revealed that in real life, with poor charging behavior from users, PHEV FC is equivalent to that of conventional vehicles, and in some cases higher, due to the increased mass and the need to keep the battery at a certain charging level. The discrepancy between official and real life figures of FC, electric range, and CO2 emissions has been often attributed, at least partly, to the inadequacy of the New European Driving Cycle (NEDC) to represent the real-world conditions of vehicle use. In an attempt to deal with this problem, which has strong implications on the effectiveness of the CO2-reduction policies, the European Commission has decided to introduce already in 2017 the Worldwide Harmonized Light Vehicles Test Procedure (WLTP). Aim of the present work is to compare WLTP and NEDC procedures for what concerns the determination of fuel consumption (FC), CO2 emissions and electric ranges of two plug-in hybrid vehicles tested in the Joint Research Centre (JRC) of the European Commission laboratories. Results show that the electric range determined following the WLTP procedure is significantly shorter than the NEDC electric range. On the contrary, results show that WLTP-based FC and CO2 will tend to be lower than the corresponding NEDC-based values with the increase in the battery size and corresponding electric range.