The clean energy transition in islands is of paramount importance in the present era of climate change. The island of Crete, Greece has rich renewable energy resources which can be deployed for power generation. The clean energy transition of Crete, Greece, after the interconnection of its electric grid has been investigated. Solar and wind energy are already used with solar-PV systems and wind farms for electricity generation in Crete covering slightly more than 20% of its annual electricity demand. The elimination of fossil fuels’ use in the electricity sector in Crete deploying endogenous renewable energies is going to assist the achievement of the national and European goal for moving to net-zero carbon emissions societies. The maximum power that can be transferred through the two undersea electric cables interconnecting the grids of Crete and continental Greece is higher than the maximum power demand in Crete which currently does not exceed 700 MW. The size of the solar-PV systems generating the same amount of electricity which is currently produced with fossil fuels in Crete is at 1,698 MWp while their cost is around 2.04 bill. e. The corresponding size and cost of the wind farms are at 940.6 MW and 0.941 bill. e. Electricity storage in Crete either in PHES systems or in large-scale electric batteries will increase its energy security. The results, indicating that the de-carbonization of the electricity sector in Crete is technically and economically feasible, could be useful to policymakers, power companies, and local authorities on the island.