## 1 Introduction
### Literature Review  
Due to the singularity of the isolated systems, the impact of battery electrical vehicles (BEVs) on isolated grids has been studied in the literature. A common characteristics of an isolated energy system is the noticeable dependence of fossil fuels (especially diesel) for power generation [13], therefore decreasing the benefit of EV adoption to reduce the overall CO\({}_{2}\) emissions. Several authors have tried to quantify reduction figures in representative small-to-medium islands. Applying a Well-to-Wheels approach, a deployment of EVs might bring CO\({}_{2}\) reductions with respect to conventional powertrains between 0 and 20% and 40 and 50% for RE penetration levels ranging from limited up to 20% [14; 15]. In addition, these studies reveal that hybrid powertrain architectures currently provide similar CO\({}_{2}\) reduction figures, requiring a much larger RE penetration to enlarge the abatement potential [16; 17; 18]. Many studies have been focused on the EV possibilities to promote the integration of renewable energy and to reinforce the grid stability [19; 20; 21]. To face the variability and uncertainty issues of the resource, there are mainly two approaches: (i) by means of controlling methods, where a limitation of the quantity of the renewable energy in the grid is achieved, or (ii) by means of energy storage systems [22], where larger energy penetration could be reached [23]. Therefore, it has been demonstrated that the BEVs can perform a two-way delivery of energy, improving the peak-shaving effect and reducing the need for conventional power plant generation [24]. On the contrary, a large deployment of BEVs entails a remarkable additional load to electrical systems, hindering the optimal management of the grid constraints and making necessary a precise planning of the grid to avoid undesirable electrical problems [25; 26; 27]. In this context, previous studies report that uncertainties in EV charging and RE resources could require up to a 30% increase in the installed power capacity from the estimated one to cover certain demands to avoid an energy shortage risk [28]. One relevant aspect is the BEV capability to act as an active element through Vehicle to the Grid (V2G), allowing the interchange of power between the electrical grid and the vehicle. The application of V2G technology can contribute to peak shaving, self-consumption, frequency control, reactive power compensation, and, when introduced in a larger scale, this technology rises the share of renewable energy in the energy mix [29]. In this sense, previous results have revealed a reduction of both grid harmonics and frequency deviation, favouring the integration of variable energy sources into power grids [30]. In addition, V2G penetration can be adequately used to avoid grid overloading and load matching [31; 32; 33],reducing the renewable energy surplus and therefore turning into a reduction of the renewable capacity needed. Other studies have highlighted the benefit of V2G penetration to reduce the undesired effects of the reactive power generated by the power electronics in various types of small- and medium-size distribution networks through a proper combination of charging stations location and management algorithms [34]. Several research works have studied decarbonisation scenarios in isolated energy systems, where the EV penetration and its interaction with the grid are not considered in detail and the HD transport demand is dismissed [35; 36; 37]. Despite the multiple contributions to the state of the art, the literature survey related to transport decarbonisation in isolated systems reflects that the majority of works have addressed specific topics. However, analysis that covers how the isolated energy system must evolve to accommodate the energy transition of the whole vehicle fleet (light- and heavy-duty) considering energy sovereignty have been dismissed.