The Role of Plug-in Hybrid Electric Vehicles in Electrifying Personal Transport

Doctoral thesis, 2023

The Paris Agreement emphasizes the importance of greenhouse gas mitigation in the transport sector to address climate change and create a sustainable future with lower carbon emissions. Plug-in hybrid electric vehicles (PHEVs) can be helpful in reducing greenhouse gas emissions in transportation when combined with efforts to decarbonize the electricity sector. PHEVs combine an electric engine with a conventional one, so they have rechargeable battery packs as well as fuel tanks. The unique position of PHEVs as a vehicle that can utilize two different energy sources makes their role in electrifying personal transport highly debated. This thesis uses various sets of real-world PHEV charging and driving data and investigates the role of PHEVs in electrifying personal transport with a focus on how much their kilometers are electrified through analysis of (1) their charging behavior and how this behavior impacts fuel consumption and tail-pipe CO2 emissions, (2) how they are driven within the household context and (3) how they are driven differently across countries.

This thesis develops a new method to identify charging events and analyze PHEV charging behavior for large samples that only have driving data. Using this method, results show that the possibility to charge overnight has a bigger effect than additional charging during the day on increasing the share of electrified kilometers of PHEVs and reducing their fuel consumption and tail pipe emissions. Therefore, it is important to ensure adequate access and incentives for users to plug-in every night to make sure PHEVs can contribute to a reduction of CO2 emissions; and policies for PHEVs should prioritize easy access to overnight charging. Results also show that PHEVs with a range of at least 56 km (35 miles) have the potential to electrify a similar share of total household miles as some short-range battery electric vehicles (BEVs) —which only have an electric engine—, or can reach up to 70% as much electrification as some long-range BEVs (e.g. Tesla Model S). On the other hand, results also show that PHEVs have poor environmental performance across the globe compared to set standards: lower share of electrified kilometers compared to type approval values and higher fuel consumption than e.g. European Union targets. However, lower electricity price to gasoline price ratio can lead to an increase in the share of electrified kilometers of PHEVs.

This thesis shows that PHEVs can considerably contribute to the share of electrified kilometers in the transport sector and play an important role in decarbonizing it if the debate regarding PHEVs is focused on maximizing their environmental benefits.