A study on flywheels materials and geometries is presented here with the use of finite element modeling (FEM) simulations. The study analyzes the stress behavior of flywheel rotors subject to the rotational speed that creates the maximum stress that the flywheel can support, and then calculates the rotational energy mass ratio for each geometry. The obtained geometry was Gaussian section for the Flywheel rotor. The material used in this case study is carbon fiber Hexcel UHM 12000. The best results were a rotational speed of ≈ 279.000 rpm and rotational energy density of ≈ 440 Wh/kg. Then, to increase the total energy, Flywheel with 2 and 3 rotors were analyzed. Then the stability under rotation of these Flywheels were analyzed, some instability was found and a solution was presented.