In these years the technology progress has allowed to increase renewable energies utilization and in the same time has contributed to raise large scale distributed generation applications. In particular the solar generation is growing and in the next future it will be always more considerable. Therefore it is important to optimize its production under different conditions (for example climatic situations), because the output characteristic of photovoltaic generators is nonlinear and changes with solar irradiation and cell's temperature. This paper presents a comparative study of seven widely-adopted MPPT algorithms; their performance is experimentally evaluated in presence of solar irradiance variations.