The transition to a fully renewable energy system in island regions poses unique challenges and opportunities. This study investigates the feasibility of achieving a 100% renewable energy supply for the Greek island of Astypalea through a Vehicle-to-Grid (V2G) hybrid energy system. By leveraging real-world data on energy demand, wind, and solar profiles, we employ PLEXOS (Energy Exemplar) simulations to explore the technical and economic requirements of such a transition. Under the assumption of complete e-mobility adoption with 1000 Electric Vehicles (EV) and 250 charging points, our analysis uses the island’s annual demand profile as a starting point to evaluate the installed renewable generation capacity and stationary battery storage required to achieve decarbonization goals. The main objective is to phase out diesel generators entirely by relying exclusively on wind and solar power, supported by stationary batteries and EVs charged with renewable energy, thereby treating EVs as distributed storage assets. We analyze three essential parameters—annual CO2 emissions (t CO2/a), percentage of renewable energy supply, and levelized cost of electricity (€/MWh)—throughout six distinct phases of capacity implementation for renewable generation and storage systems. The findings indicate that achieving 100% renewable supply is technically viable in the latest phase only when complemented by a backup Diesel generator to ensure supply security. However, the financial implications associated with the realization of such a system’s phase are not convenient. Nevertheless, a specific configuration of installed renewable energy capacity and storage, supported by V2G infrastructure, presents the most economically advantageous outcome for the energy systems economy. This configuration suggests a potential cost saving of 30% and a reduction in CO2 emissions by 87.97% compared to the first development phase currently in place.