This paper deals with the feasibility of a Renewable Energy Sources (RES)-based stand-alone system for electricity supply based on a Flywheel Energy Storage System (FESS) located on the Greek Island of Naxos. The innovative use of flywheels in parallel connection with electrochemical batteries, as an integrated storage device in the same power plant, was selected to be simulated as it is a necessary buffer covering the load of a typical house. The optimal configuration for the electromechanical connection between the electrochemical batteries and flywheels is also considered in this study. Operational characteristics of the new storage systems were estimated and used in the simulations, while the financial aspects of the projects finalized using hand-made calculations and the HOMER software was used only for the energy calculations. It was found that an off-grid project using advanced and totally “green” technologies is possible and comparable to more conventional RES-based systems, in terms of energy and economical feasibility. Finally, it can be concluded that systems with low price flywheels are equivalent to those with electrochemical batteries.