This paper presents a new method for the optimal sizing of photovoltaic systems in distribution networks, in order to reduce energy losses and improve the voltage profile. The DIgSILENT PowerFactory software, specifically the DIgSILENT programming language (DPL) was used for implementation of this method. Photovoltaic systems are modeled as constant power, and the optimization method has the ability to determine the sizing for distributed generation units. The effectiveness of the method was tested in the 60-bus insolated electrical system of Iquitos with excellent results, which are discussed and commented.