## 5 Conclusions and Policy Implications  
This paper explores a 100% renewable energy supply scenario for both power-generation and road transport sectors in the island of Tenerife. Representative of medium isolated energy systems, Tenerife island represents an excellent test case as both methodology and results can be completely transferable to the rest of isolated systems worldwide. The island's energy system was modelled in EnergyPLAN, and validated against published data obtained from official governmental sources. Starting from the reference scenario and taking into account the current renewable technology roadmap, the impact of a full deployment of zero-tailpipe-emission vehicles on the energy system was evaluated under the consideration of an autonomous renewable energy supply. Autonomous decarbonisation of the power-generation sectors implies a large deployment of renewable power capacity. The characteristics of these highly variable technologies, together with the nature of an isolated system, turn into high levels of curtailment (above 27%), even when considering energy storage systems. A significant back-up energy provided by dispatchable gen-sets fed by H\({}_{2}\) will be required to cover demand during renewable intermittency events. The internal H\({}_{2}\) production via electrolysis requires significant capacities that exhibit low equivalent hours of operation. The impact of a complete technology shift in the transport sector (light- and heavy-duty) was analysed in detail. To accommodate the additional energy demand, the renewable capacity must experience a significant growth (more than 30%), requiring additional storage capacity to avoid excessive curtailment. Although the presence of V2G functionality in 30% of the light-duty fleet allows a slight reduction of the required back-up energy, the same deployment of renewable and energy storage sources is required. The analysis of the heavy-duty fleet reveals that large H\({}_{2}\) shares are beneficial for the energy system, as electrolysers' dispatch approach prioritises events of high availability of renewable energy. This behaviour eventually allows reducing the power and storage capacity to be installed. In light of this, several recommendations to policy makers could be suggested:  
* Energy demand reduction as a first objective. Although the results evince that a full autonomous energy supply is possible, the amount of RE to be deployed is massive. This results in a significant amount of electrical energy spilled and large EES capacities, which might put the profitability of the RE producers at risk. * Dispatchable RE sources must be prioritised. Given the space constraints of the island, high enthalpy geothermal resources arise as the main opportunity on the island, which  
Figure 8: RE capacity deployment rate in the 2025–2050 time frame to reach decarbonisation with a fully autonomous RE supply. require government boosting in terms of economic support during exploration and future exploitation (if it exists). * The use of imported energy vectors to support internal demands. In this context, energy carriers such as drop-in fuels could play a key role in transportation. Their high energy density and the fact that can be used with existing technologies and infrastructure make these renewable fuels an excellent option to reduce the RE and ES requirements on the island. Without a doubt, the viability of this route must be studied in depth and it will eventually depend on how the power-to-fuel process maturity evolves. Future research work includes a deeper analysis of different paths to reach decarbonisation on the island. Energy demand reductions in specific sectors and the comparison of additional scenarios that consider a partial dependence on energy vectors for transportation and/or power-generation will be evaluated. Every solution, to be optimised, must be quantified in terms of economic costs, deployment feasibility, and CO\({}_{2}\) abatement effectiveness. Conceptualisation, I.S.-M. and O.G.-A. ; methodology, I.S.-M. and O.G.-A.