This paper presents a method of sizing photovoltaic panels using modified particle swarm optimization (MPSO) in order to reduce energy losses and improve the voltage profile. The proposed method was applied to the IEEE 13-bus distribution network, and finally was validated using the real micro grid of the Federal University of Paraiba (UFPB). The results show that the proposed method has the ability to provide sizing of photovoltaic modules distributed in a micro grid, improving the voltage profile and reducing energy losses.