Empirical fuel consumption and CO2 emissions of plug-in hybrid electric vehicles

Plug-in hybrid electric vehicles (PHEVs) combine electric and conventional propulsion. Official fuel consumption values of PHEVs are based on standardized driving cycles, which show a growing discrepancy with real-world fuel consumption. However, no comprehensive empirical results on PHEV fuel consumption are available, and the discrepancy between driving cycle and empirical fuel consumption has been conjectured to be large for PHEV. Here, we analyze real-world fuel consumption data from 2,005 individual PHEVs of five PHEV models and observe large variations in individual fuel consumption with deviation from test-cycle values in the range of 2% to 120% for PHEV model averages. Deviations are larger for short-ranged PHEVs. Among others, range and vehicle power are influencing factors for PHEV model fuel consumption with average direct carbon dioxide (CO2) emissions decreasing by 2% to 3% per additional kilometer (km) of electric range. Additional simulations show that PHEVs recharged from renewable electricity can noteworthily reduce well-to-wheel CO2 emissions of passenger cars, but electric ranges should not exceed 200 to 300 km since battery production is CO2-intense. Our findings indicate that regulations should (1) be based on real-world fuel consumption measurements for PHEV, (2) take into account charging behavior and annual mileages, and (3) incentivize long-ranged PHEV.