Making sense of life cycle assessment results of electrified vehicles

Battery electric vehicles and plug-in hybrid electric vehicles can have life-cycle carbon dioxide emissions that can be close, within 5 % of each other, or very different depending on the efficiencies of the powertrain, relative contributions of battery and combustion engine to the traction power, and source of electricity. Life cycle assessments can provide insight into the variability in carbon dioxide emissions, but they are time consuming. In this work a simplified model that can explain the carbon dioxide emissions during the well-to-wheels portion of the life cycle is developed. The robustness of the simplified model is evaluated by varying parameters and comparing its results with those from the life cycle assessment. Assumptions must be made to conduct the assessment. The assumptions include the efficiencies of the internal combustion engine, the battery, the drivetrain, and regenerative braking, and the relative contribution of the battery to traction power in the plug-in hybrid electric vehicle. Renewable and non-renewable sources of generating electricity are considered. It is concluded that a plug-in hybrid electric vehicle with the same parameters as the battery electric vehicle can potentially be lower emitting only when the emissions factor of the electricity generation and the internal combustion engine efficiency are high. For low carbon intensity electricity generation, the plug-in vehicle emits more carbon dioxide than the battery electric vehicle for the range of internal combustion engine efficiencies considered.