Prospective life-cycle assessment of greenhouse gas emissions of electricity-based mobility options

Abstract

Electricity-based mobility (EBM) refers to vehicles that use electricity as their primary energy source either directly such as Battery Electric Vehicles (BEV) or indirectly such as hydrogen (H2) driven Fuel Cell Electric Vehicles (FCEV) or Synthetic Natural Gas Vehicles (SNG-V). If low-carbon electricity is used, EBM has the potential to be more sustainable than conventional fossil-fuel based vehicles. While BEV feature the highest tank-to-wheel efficiency, electricity can only be stored for short durations in the energy system (e.g. via pumped-hydro storage or batteries), whereas H2-FCEV and SNG-V have a lower tank-to-wheel efficiency due to additional conversion losses, H2 and SNG can be stored longer in pressurized tanks or the natural gas grid. Thus, they feature more flexibility with regard to exploiting renewable electricity via seasonal storage. In this study, we examine whether and under what circumstances this additional flexibility of H2 and SNG can be used to offset additional losses in the powertrain and conversion with respect to greenhouse gas (GHG) mitigation of EBM from a life-cycle point of view in a Swiss scenario setting. To this end, a supply chain model for EBM fuels is established in the context of an evolving Swiss and European electricity system along with an approach to estimate the penetration of EBM in a legislation compliant future passenger cars fleet. We show that EBM results in significantly lower life-cycle GHG emissions than a corresponding fossil fuels driven fleet. BEV generally entail the lowest GHG emissions if flexibility options can be offered through sector coupling, short-term and seasonal energy storage or demand side management. Otherwise, in particular with a large expansion of photovoltaics (PV) and curtailment of excess electricity, H2-FCEV and SNG-V feature equal or – in case of high-carbon electricity imports – even lower GHG emissions than BEV.