This work investigates the feasibility of a renewable energy sources (RES)-based stand-alone power system for electricity supply, to several simulated buildings, where energy is stored in a flywheel energy storage system (FESS). The system is assumed to be located on Naxos Island, Greece, due to the island’s high wind and solar potential and was designed to cover both the load of a typical house and a country house, where the excess electricity could be sold to the grid. An innovative storage device type, consisting of flywheels and electrochemical batteries, was selected as the energy buffer. The energy produced by hydrogen used in the proton electrolyte membrane (PEM) fuel cell (FC) charges the flywheel. This apparatus is compared to diesel generators commonly used in stationary applications. Optimization of the system, in terms of energy efficiency and economic feasibility, is also considered. The two systems were simulated using sensitivity, optimization, and simulation modeling software, and custom calculations of both energy and finance were carried out. It was found that a one-way grid connected project using state-of-the-art and totally green technologies, including hydrogen-fed PEM-FC and flywheels, can totally cover the electrical demands of a typical house and country house, obtaining cost per consumed energy as low as 1.374 and 0.097 $/KWh, respectively. These results actually indicate that hydrogen technology could be a reliable energy alternative in the near future.