This report presents the work done during my internship at the IMEP-LaHC and LMGP laboratories. The use of batteries in electronic devices has been widely spread these last few years, although causing environmental issues. The goal is then to find alternative solutions using the energy available everywhere around us: mechanical energy. This internship is focused on the study of NGs based on piezoelectric ZnO NWs fabricated by MOCVD. The objectives are the fabrication, simulation and characterization of devices transforming mechanical energy into electrical energy, using the piezoelectric effect coming from the NWs. The simulation, using the finite element method (COMSOL multiphysics), allows to optimize the device by varying different parameters (size of the NWs, density of charges...).