This paper proposes a dynamic model for evaluation of a Pumped Storage Project (PSP) . The optimal expansion policy is determined by considering different alternatives (Types of units: Rodbar PSP(RPSP), Steam Turbine , 2 types of Gas Turbine and a Combined Cycle) . Based on this model dynamic assessment of different alternatives (over a 20 years period and with a target Loss Of Load Probability (LOLP)) provides economic justification for RPSP.