لخّصلي

Electric and hybrid powertrains are currently regarded as promising emerging technologies for propulsion of vehicles with potential to reduce greenhouse and other exhaust gas emissions from road transport (Nemry and Brons 2010; Sadek 2012). The arguments are that electric powertrains are more energy efficient for propelling vehicles than conventional internal combustion engines fuelled by petrol or diesel, and that full electric propulsion does not emit tailpipe emissions (IAE 2011; Sadek 2012). In addition, electric powertrains can assist in decoupling the transport sector from its heavy reliance on fossil fuels. On the other hand, electric vehicles may require additional electricity production (Tran et al. 2012) and this can be done using several different energy sources with diverse environmental impacts. Furthermore, electric powertrains require new advanced components (Chan 2007), causing additional, or at least different, environmental impacts compared to conventional vehicles.

The trade-off between the benefits when operating the vehicle and possible new or increased negative impacts from production and from energy supply can be analyzed using life cycle assessment (LCA). However, LCA studies come in many shapes and cause diverging arguments about the environmental performance of the technology on which they are based. Some advocate the technology, for example, using the well-to-wheels approach to guide government promotion policies toward different types of powertrains and alternative fuel options (Ou et al. 2010b). Others claim that the prospective for electric cars to reduce the environmental impacts of mobility is “substantially overrated” (Frischknecht and Flury 2011) or that they will lead to “significant increases in human toxicity” (Hawkins et al. 2013a).

Few reviews have been carried out in the field of LCA of electric vehicles, synthesizing results and assessing the scope of the research field. In the most thorough, Hawkins et al. (2012) benchmarked 55 studies and surveyed what 51 of them cover in terms of scope compared to their own recommended practice and definition of a state-of-the-art complete LCA of electrified vehicles. The review commendably discusses and evaluates the datasets used in the research field, and identifies gaps in the inventories of the main components such as batteries, electric motors, and electronic equipment. It also presents an analysis of greenhouse gas (GHG) emissions for the complete life cycle across studies, including meta-analysis of the effect of assumptions regarding lifetime on impact from production of equipment and discussions on how battery production and use phase energy efficiency affect the results. Additionally, the history of life cycle assessments of electrified vehicle is summarized; various technical aspects of vehicle electrification such as charging management is described and uncertainty in results is discussed. Among conclusions, Hawkins et al. (2012) do not find any of the reviewed 51 studies to comply with their definition of how a complete state-of-the-art LCA of electrified vehicles should be conducted, and hence request more rigorous and complete inventories and studies. The quality of “stylized studies,” described as studies based on rudimentary inventories and a low level of detail, is questioned. It is argued that such studies have limited utility for informing policy makers as they only cover limited subsets of the complete system (Hawkins et al. 2012).

Another paper by Helmers and Marx (2012) compiles a broad description of technical characteristics and environmental impacts of electric and hybrid vehicles, however without focus on literature evaluation. They conclude that electric vehicles have many benefits over conventional ones, but that the LCA literature on the subject “is complex.” Overviews are also provided in a conference report by Frischknecht and Flury (2011), in an appendix to a case study by Ma et al. (2012) and an editorial by Althaus (2012). Althaus (2012) observes that results come out as diverging and that there is “a rather weak consensus” on the environmental performance of electric vehicles. Also, Frischknecht and Flury (2011) argue that results are diverging and, as an example, mention that emissions for electric vehicles vary between 95 to 240 g CO2-eq./km.

In contrast, we argue that the numerical results in any system study, such as LCA, is dependent on its purpose or, more to the point, which specific problem or question it is investigating (see for example Sterman (1991)). In LCA, the formulation of the purpose is made during what the international standard for LCA (ISO 2006a, b) defines as the goal and scope definition. The scope consists of the methodological choices made to address the stated goal, ensuring that the conclusions of the study are sufficiently supported, for example in selection of technical scope, time horizon, and level of impact assessment. But, from going through the literature in the field, it is evident that while the scope (i.e., the modeling choices) at large, except for the time frame, is mostly well described in LCA studies of electric and hybrid vehicles, the goal is sometimes expressed vaguely and even partly, or fully, left out. As a consequence, there is a risk that the research field appears unnecessarily complex and provides seemingly diverging results, in particular if common messages are sought from studies with very different goal and scope. Unclearly articulated purposes of studies make it necessary to go into the details of each study to find the motivation for its limitations and underlying assumptions. This may also disguise that consensus can be found in several main conclusions from studies with similar scope. As a consequence, stakeholders within the area of vehicle electrification, such as policy makers and various branches of industry, might end up without guidance when it could have been, and was intended to be, given.