Research and development activities in the field of renewable energy have been considerably increased in many countries recently, due to the worldwide energy crisis. Wind energy is becoming particularly important. Although considerable progress have already been achieved, the available technical design is not yet adequate to develop reliable wind energy converters for conditions corresponding to low wind speeds and urban areas. The Savonius turbine appears to be particularly promising for such conditions, but suffers from a poor efficiency. The present study considers improved designs in order to increase the output power of a classical Savonius turbine. It aims at improving the output power of the Savonius turbine as well as its static torque, which measures the self-starting capability of the turbine. In order to achieve both objectives, many designs have been investigated and optimized by placing in an optimal manner an obstacle plate shielding the returning blade. The geometry of the blade shape (skeleton line) has been optimized in presence of the obstacle plate. Finally, frontal guiding plates have been considered and lead to a superior performance of Savonius turbines. The optimization process is realized by coupling an in-house optimization library (OPAL, relying in the present case on Evolutionary Algorithms) with an industrial flow simulation code (ANSYS-Fluent). The target function is the output power coefficient. Compared to a standard Savonius turbine, a relative increase of the power output coefficient by 58% is finally obtained at design point. The performance increases throughout the useful operating range. The static torque is found to be positive at any angle, high enough to obtain self-starting conditions. Considering now ocean's and sea's energy, the Wells turbine is one of the technical systems allowing an efficient use of the power contained in waves with a relatively low investment level. It consists of a self-rectifying air flow turbine employed to convert the pneumatic power of the air stream induced by an Oscillating Water Column into mechanical energy. On the other hand, standard Wells turbines show several well-known disadvantages: a low tangential force, leading to a low power output from the turbine; a high undesired axial force; usually a low aerodynamic efficiency and a limited range of operation due to stall. In the present work an optimization process is employed in order to increase the tangential force induced by a monoplane and two-stage Wells turbine using symmetric airfoil blades as well as by a two-stage Wells turbine using non-symmetric airfoil blades. The automatic optimization procedure in this part of the work is again carried out by coupling the in-house optimization library OPAL with the industrial CFD code ANSYS-Fluent. This multi-objective optimization relying on Evolutionary Algorithms takes into account both tangential force coefficient and turbine efficiency. Detailed comparisons are finally presented between the optimal designs and the classical Wells turbine using symmetric airfoils, demonstrating the superiority of the proposed solutions. The optimization of the airfoil shape lead to a considerably increased power output (+12%) and simultaneously to an increase of efficiency throughout the full operating range.