In an open-access paper published in Scientific Reports, a team from Fraunhofer ISI and KIT (Karlsruhe Institute of Technology) has presented the first systematic overview of empirical findings on the electrification of vehicle mileage based on on actual PHEV (plug-in hybrid) and BEV (battery-electric vehicle) usage for the US and Germany. The team found that, contrary to common belief, a PHEV with about 60 km (37 miles) of real-world range currently electrifies as many annual vehicles kilometers as a BEV, despite having a much smaller battery.
Further, they found that when the higher CO2eq emissions generated during the production phase of BEVs compared to PHEVs (due to the much larger BEV battery) are included in the analysis, a PHEV today shows higher CO2eq savings then BEVs compared to conventional vehicles. For significant ongoing CO2eq improvements of PHEVs—and particularly of BEVs—the decarbonization of the electricity system needs to continue, the researchers said.
For the study, the team compared the performance of 49,000 BEVs and 73,000 PHEVs in Germany and the US. The data are taken from fleet trials and automobile manufacturers as well as websites used by drivers to manage and monitor their own vehicles.
|Average electrified annual kilometres for different PHEV (green) and BEV (red) models from the US (squares) and Germany (circles). The shaded areas are sample size weighted local smoothers (95% confidence bands). © Fraunhofer ISI. Click to enlarge.|
Analyzing the data showed that plug-in hybrids with a real-world electrical range of about 60 kilometers drive the same number of kilometers electrically as battery electric vehicles—up to 15,000 kilometers (9,321 miles) each year. Their CO2 reduction potential is therefore just as large as battery electric cars, the researchers said.
|Overall distribution of daily VKT for a large daily driving data set. Also shown are the annual electrified VKT by BEV and PHEV with typical ranges as shaded areas under the curve. Click to enlarge. Plötz et al.|
In the paper, the authors observed that when more fast charging stations become available, BEVs will increase their electrified VKT significantly as more trips will become feasible with intermediate charging. This implies that more long range trips could be electrified by a BEV. Although, in principle, a PHEV could also recharge during long-distance trips, the small relectric range would require many breaks for recharging and users might prefer to refuel their fuel tank instead.
Plug-in hybrid vehicles represent a good addition to battery electric cars in order to meet the goal of reducing greenhouse gases. They have often been judged too critically in the past based on insufficient empirical data. However, it is important that they have a sufficiently large battery with a real electrical range of more than 50 kilometers and, in addition, that the decarbonization of the electricity system continues to be advanced.—Dr. Patrick Plötz, who leads the study at Fraunhofer ISI
On the lifecycle analysis side, the researchers pointed out that today, one kWh of battery capacity results in about 100 kg CO2eq emissions during its construction phase. Thus, the additional construction phase emissions for the battery are smaller for a PHEV (on average 0.6 t of CO2eq) than for BEV (on average 2.6 t of CO2eq). However, PHEVs also include internal combustion engines and complex gear boxes, which lead to additional emissions of about 0.6 t of CO2eq per vehicle during the construction phase.
Thus, currently the overall CO2eq emissions from vehicle construction are about 1.4 t higher for BEV than for PHEV. Learning effects in battery production together with an improved electricity mix might even decrease this disadvantage in the future.—Plötz et al.
According to the study, the decreasing CO2 emissions during battery production and the increasing diffusion of rapid charging points will shift this advantage more and more in the direction of battery-electric vehicles in the coming years.
The study was conducted within the framework of the “Profilregion Mobilitätssysteme Karlsruhe” (Profile Region Mobility Systems Karlsruhe). Fraunhofer ISI and regional research partners are pooling their expertise in this think tank to develop efficient, intelligent and integrated mobility solutions.
P. Plötz, S. A. Funke, P. Jochem & M. Wietschel (2017) “CO2 Mitigation Potential of Plug-in Hybrid Electric Vehicles larger than expected” Scientific Reports 7, Article number: 16493 (2017) doi: 10.1038/s41598-017-16684-9