The growing concerns about climate change and security of supply opened way to a significant investment in the exploitation of RES (renewable energy sources) for electricity generation. The possibility of achieving 100% RES systems is being debated but concerns about costs, storage and backup capacity still prevail. This paper addresses the topic of renewable energy scenarios for the electricity sector, analyzing different possible future strategies for the Portuguese system. Each one of these strategies is characterized according to the expected electricity consumption and renewable share, with the final aim of analyzing a possible 100% RES scenario. The energy system analysis tool EnergyPLAN was used for simulating each scenario for a one year period. The 100% RES scenario is found to be theoretically possible but a significant increase on the total capacity of the system would be necessary to ensure no shortfall during the summer season. The outcome would be the existence of critical excess electricity production during the winter and also a significant increase of the total cost of the system. The importance of the interconnection as stabilization measure along with the inclusion of storage systems is discussed for a system highly dependent on renewable energy sources. (C) 2014 Elsevier Ltd. All rights reserved.