Circumventing limitations to transport energy efficiency – the electric car in two-car households

Panel: 4. Mobility, transport, and smart and sustainable cities

This is a peer-reviewed paper.

Author:
Sten Karlsson, Chalmers University of Technology, Department of Energy and Environment, Sweden

Abstract

The electrification of vehicles may lead to considerably lower energy use in transportation due to the high energy efficiency of electric driveline. The deployment of electric cars is hampered by the limited range of current battery electric drivelines. Larger batteries are costly and require energy in production that counteracts the energy gains from the additional driving that is made possible. In multi-car households, the battery electric vehicle (BEV) may drive more while keeping the battery size down by utilising the options of replacing more than one car’s driving and having a back-up for longer distances.

An optimisation model is developed to estimate the potential for a BEV, when replacing one of the conventional cars, to viably contribute to the accomplishment of the driving in two-car households. It uses data from 1 to 3 months of simultaneous GPS logging of the movement patterns for both cars in 64 commuting two-car Swedish households.

The results show that a flexible vehicle use strategy fully utilising the available options can considerably increase BEV driving, almost eliminating the driving not possible to fulfil due to the range and charge limitations. This flexibility combines with a smaller BEV battery and results in significantly better BEV economics compared to a car-for-car-only BEV substitution. We estimate the present value of this flexibility on average to around $6-7000 in Swedish two-car households. The achieved fuel savings amounts to around 11 GJ/yr per household corresponding to a mitigation of around 770 kg CO2/yr.