# Electricity Generation in LCA of Electric Vehicles: A Review
## 3 Spatial boundary.
#### 3.2.2. Attributed System Modelling  
While there is no biunivocal link between marginal mixes and consequential studies, ALCA studies are more straightforward. All the attributional studies apply the average national mix, and they mainly model it as background processes using renowned databases (EcoInvet, GREET, eGRID... ). Other sources are Transmission System Operators (TSO), Distribution System Operators (DSO), national and regional statistics etc. No author provides explanations for the modelling choice when performing ALCAs, probably because it is perceived as the norm in scientific literature, due to its overwhelming majority among LCA papers [86]. The identification of the average mix is methodologically less equivocal, since it represents the total generation allocated evenly to the total load. However, various sources of variability can be listed:  
* Data quality: Transparent and up-to-date electricity data are not the norm. Especially when relying on background databases, studies tend to overlook the data quality of the selected dataset. * Regional boundary: The region of production of electricity and that of consumption do not always coincide. Selecting the adequate regional boundary is a trade-off between representativeness and the problem of modelling cross boundary flows. * Time: Generally temporal granularity in attributional LCA is one year. However also for average electricity mixes, there can be significant differences from one year to another. To overcome this obstacle, some studies average the emissions over a longer time span. * Future scenarios' definition and stylised states adoption. (A'stylised state' is denoted an extreme state (e.g. a state where all electricity and heat is produced from coal) that is unlikely to materialise but that could illustrate important technology differences in a clear way [87]). Data Quality  
Data on electricity mix are provided from DSO and TSO, national and international agencies (EPA, German federal environmental agency, IEA) or are derived from databases. The former generally provide more updated data (usually from the previous year) than the latter; also, studies gathering data on electricity from energy operators are generally aware of the relevance of these data in the overall results. When relying on data from databases, studies do not provide the emission intensity of the selected mix. Obtaining it a posteriori is either time demanding or impossible because database versions are not always made explicit [14] and the selected dataset is rarely expounded (an exception is the study by [PERSON] et al. [16]). Ignoring the database version and the dataset selected for the electricity mix, besides contravening the basic principle of reproducibility of LCA, makes it difficult to understand the results and the role played by electricity. Selecting one dataset or another can lead to relevant differences. In Figure 4, the g CO\({}_{2}\)-eq/kWh are reported according to different datasets and versions of EcoInvent for the main countries analysed in the literature regarding EVs. This is to show how much datasets from the same database can differ. EcoInvent database has been selected for exemplification sake because of its widespread use in LCA of EVs. When relying on databases, studies overlook the quality of the data and their time period. Seven of the revised papers adopt EcoInvent as a background database; and among those, five rely on the version 2.2. Data on electricity supply mix from EcoInvent v.2.2 were updated to 2004, meaning that some papers published in 2017 still rely on electricity mix data from that year [16,18]. Geographical Boundary  
Most of the studies use mixes which have been aggregated at national level or at regional and subcontinental level, trying to follow the electricity infrastructure and trade (PJM) regions in the US, ENTSO-E in Europe, NORDEL in Scandinavia, etc.). The definition of the regional boundary has relevant influence on the final result: [PERSON] et al.