Clean and sustainable renewable energy technology is going to take responsibility of energy supply in electrical power systems. Using renewable sources improve the environment and reduce dependence on oil and other fossil fuels. In distribution power system, utilizing of wind and solar DGs comprises some advantages; consist of loss and emission reduction, and also improvement of voltage profile. So, in expansion planning of distributed generations, improvement of each of these parameters can be the objective of planner. In this paper, a mathematical model for sizing and placement of wind and solar DGs is proposed. The formulation is based on a probabilistic load-generation model. The stochastic nature of the wind and solar resources are considered in the proposed scenario-based model. This mathematical framework is used to minimize total annual loss as an objective function. All the network constraints in different operational conditions are regarded. The model is applied on a typical rural distribution network using GAMS software which illustrated the effectiveness of the model. پرونده مقاله