A new hybrid method for reducing the gap between WTW and LCA in the carbon footprint assessment of electric vehicles

Abstract

Purpose The well-to-wheel (WTW) methodology is widely used for policy support in road transport. It can be seen as a simplified life cycle assessment (LCA) that focuses on the energy consumption and CO 2 emissions only for the fuel being consumed, ignoring other stages of a vehicle's life cycle. WTW results are therefore different from LCA results. In order to close this gap, the authors propose a hybrid WTW+ LCA methodology useful to assess the greenhouse gas (GHG) profiles of road vehicles. Methods The proposed method (hybrid WTW+LCA) keeps the main hypotheses of the WTW methodology, but integrates them with LCA data restricted to the global warming potential (GWP) occurring during the manufacturing of the battery pack. WTW data are used for the GHG intensity of the EU electric mix, after a consistency check with the main life cycle impact (LCI) sources available in literature. Results and discussion A numerical example is provided, comparing GHG emissions due to the use of a battery electric vehicle (BEV) with emissions from an internal combustion engine vehicle. This comparison is done both according to the WTW approach (namely the JEC WTW version 4) and the proposed hybrid WTW+LCA method. The GHG savings due to the use of BEVs calculated with the WTW-4 range between 44 and 56 %, while according to the hybrid method the savings are lower (31-46 %). This difference is due to the GWP which arises as a result of the manufacturing of the battery pack for the electric vehicles. Conclusions The WTW methodology used in policy support to quantify energy content and GHG emissions of fuels and powertrains can produce results closer to the LCA methodology by adopting a hybrid WTW+LCA approach. While evaluating GHG savings due to the use of BEVs, it is important that this method considers the GWP due to the manufacturing of the battery pack.

Sensitivity Analysis in the Life-Cycle Assessment of Electric vs. Combustion Engine Cars under Approximate Real-World Conditions

“…Finally, the EV is modelled based on two alternative electricity choices depicting the use phase: (1) Average net electricity from 2013 in Germany, which, regarding its power plant mix and climate change (CC) impact, is close to the European average mix [5]. (2) A realistic German renewable electricity mix of the future, called DE 2050 (Table 1).…”

Advances and critical aspects in the life-cycle assessment of battery electric cars

“…22 The WTW methodology can be seen as a simplified LCA that focuses on the fuel but ignores the production and end-of-life treatment of the vehicle. 23 To account for the energy-intensive production of batteries, Moro and Helmers 22 proposed a hybrid method that extends the conventional WTW analysis by incorporating the energy use and GHG emissions of battery production.…”

“…54 "BEV medium carbon" scenario is based on the EU27 electricity carbon footprint of 540 g CO 2 /kWh in 2009; 40 "BEV EU27 2030" scenario assumes a carbon footprint of 211 g CO 2 equiv/ kWh (prediction); 60 "BEV low carbon" scenario assumes a carbon footprint of 150 g CO 2 equiv/kWh (rounded from Helmers et al 44 ). We add 18.3 g CO 2 equiv/ km 22 to each BEV scenario to account for the carbon footprint of the battery. Abbreviations: BEV, battery electric vehicle; CtL, coal-to-liquid; ICEVs, internal combustion engine vehicles; V2G, vehicle-to-grid.…”

Preface

“…& Assessing the use phase of EVs (Moro and Helmers 2016;Helmers et al 2016), & Resource driven assessments (Gemechu et al 2016;Pehlken et al 2016;Hernandez et al 2016), & The potential of EVs for energy storage systems in the smart grid as a cascading use option (Gemechu et al 2016;Richa et al 2016;Casals et al 2016), and & The assessment of fuel cell electric vehicles (Miotti et al 2016).…”

“…Focusing in more detail on the fuel consumption and energy savings, Moro and Helmers (2016) present a novel hybrid method for reducing the gap between well-to-wheel (WTW) and LCA in the carbon footprint assessment of electric vehicles. Their proposed method (hybrid WTW + LCA) keeps the main hypotheses of the WTW methodology, but integrates them with LCA data restricted to the global warming potential (GWP) occurring during the manufacturing of the battery pack.…”