The main goal in design of grid connected photo voltaic systems is to maximize the energy generation based on local energy requirements, weather conditions, economic and social impact. These factors ought to be taken into account to perform a model that allow design grid-connected photo voltaic systems. In this paper a design-dimensioning model for a small grid-connected photo voltaic systems is developed. This model is based on energy conditions instead of power conditions. There are shown the two main trends that are typically used in the design process and the calculation of the two main components of the system (generator and inverter). An example of the design for a system located in Bogota-Colombia is studied.