Energy storage constitutes an effective way to manage excess RES production, and pumped storage is a suitable and mature solution for large storage capacities. The present study aims to investigate the performance of a pumped storage unit introduced in a conventional Hydroelectric Power Plant in Greece. At first, the plant operation and the electric grid data for a reference period of one year are used to compute the time variation of water inflow into the dam, and to estimate the RES production rejections depending on the installed power. Next, a pumping station powered by the rejected RES production and raising water from an adjacent downstream reservoir is modeled. Various scenarios concerning the pumping station power rate and feeding program are examined. The operation of the combined system is simulated in detail and the energy results are analyzed. Also, an economic evaluation is carried out based on current financial conditions in Greece. The results showed that a considerable amount of excess RES production can be stored, but the economic viability of the investment depends on some critical parameters, which are identified. Certain guidelines concerning the optimum sizing and operation strategy of the pumped storage scheme are finally extracted. (C) 2012 Elsevier Ltd. All rights reserved.